changelog for 0.9.1

[posh.git] / posh.xml

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<refentry id='posh'>
    <refmeta>
        <refentrytitle>POSH</refentrytitle>
        <manvolnum>1</manvolnum>
        <refmiscinfo class='date'>January 24, 2011</refmiscinfo>
        <refmiscinfo class='manual'>User commands</refmiscinfo>
    </refmeta>
    <refnamediv id='name'>
        <refname>posh</refname>
        <refpurpose>Policy-compliant Ordinary SHell</refpurpose>
    </refnamediv>
    <refsynopsisdiv id='synopsis'>
        <cmdsynopsis>
            <command>posh</command>
            <arg choice='opt'>+-aCefilnuvx </arg>
            <arg choice='opt'>+-o <replaceable>option</replaceable></arg>
            <arg choice='opt'><arg choice='opt'><arg choice='plain'>-c <replaceable>command-string</replaceable></arg><group choice='plain'><arg choice='opt'><replaceable>command-name</replaceable></arg><arg choice='plain'>-s </arg><arg choice='plain'><replaceable>file</replaceable></arg></group></arg><arg choice='opt' rep='repeat'><replaceable>argument</replaceable></arg></arg>
        </cmdsynopsis>
    </refsynopsisdiv>

    <refsect1 id='description'><title>DESCRIPTION</title>
        <para>
            <emphasis remap='B'>posh</emphasis> is a reimplementation of the Bourne shell, a command
            interpreter for both interactive and script use.
        </para>

        <refsect2 id='shell_startup'><title>Shell Startup</title>
            <para>
                The following options can be specified only on the command line:
            </para>
            <variablelist remap='.IP'>
                <varlistentry>
                    <term><option>-c</option> <replaceable>command-string</replaceable></term>
                    <listitem>
                        <para>
                            the shell executes the command(s) contained in <emphasis remap='I'>command-string</emphasis>
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><option>-i</option></term>
                    <listitem>
                        <para>
                            interactive mode &mdash; see below
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><option>-l</option></term>
                    <listitem>
                        <para>
                            login shell &mdash; see below
                            interactive mode &mdash; see below
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><option>-s</option></term>
                    <listitem>
                        <para>
                            the shell reads commands from standard input; all non-option arguments
                            are positional parameters
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>
                    In addition to the above, the options described in the
                    <command>set</command> builtin
                command can also be used on the command line.
            </para>

            <para>
                If neither the <option>-c</option> nor the <option>-s</option> options are specified, the
                first non-option argument specifies the name of a file the shell reads
                commands from; if there are no non-option arguments, the shell reads
                commands from standard input.
                The name of the shell (<emphasis remap='I'>i.e.</emphasis>, the contents of the <emphasis remap='B'>$0</emphasis>) parameter
                is determined as follows: if the <option>-c</option> option is used and there is
                a non-option argument, it is used as the name; if commands are being
                read from a file, the file is used as the name; otherwise the name
                the shell was called with (<emphasis remap='I'>i.e.</emphasis>, argv[0]) is used.
            </para>

            <para>A shell is <emphasis remap='B'>interactive</emphasis> if the <option>-i</option> option is used or
                if both standard input and standard error are attached to a tty.
                An interactive shell has job control enabled (if available),
                ignores the INT, QUIT and TERM signals, and prints prompts before
                reading input (see <envar>PS1</envar> and <envar>PS2</envar> parameters).</para>

            <para>A shell is <emphasis remap='B'>privileged</emphasis> if the <option>-p</option> option is used or if
                the real user-id or group-id does not match the effective user-id
                or group-id (see <citerefentry><refentrytitle>getuid</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
                <citerefentry><refentrytitle>getgid</refentrytitle><manvolnum>2</manvolnum></citerefentry>).
                A privileged shell does not process $HOME/.profile.
                Instead the file /etc/suid_profile is processed.
                Clearing the privileged option causes the shell to set its effective
                user-id (group-id) to its real user-id (group-id).</para>

            <para>If the basename of the name the shell is called with (<emphasis remap='I'>i.e.</emphasis>, argv[0])
                starts with <emphasis remap='B'>-</emphasis> or if the <option>-l</option> option is used, the shell is assumed
                to be a login shell and the shell reads and executes the contents of
                <filename>/etc/profile</filename> and
                <filename>$HOME/.profile</filename> if they exist and are readable.</para>

            <para>The exit status of the shell is 127 if the command file specified
                on the command line could not be opened, or non-zero if a fatal syntax
                error occurred during the execution of a script.
                In the absence of fatal errors, the exit status is that of the last
                command executed, or zero, if no command is executed.</para>
        </refsect2>

        <refsect2 id='command_syntax'><title>Command Syntax</title>
            <!-- {{{  words and tokens -->
            <para>The shell begins parsing its input by breaking it into words.
                Words, which are sequences of characters, are delimited by unquoted
                white-space characters (space, tab and newline) or meta-characters
                (<token>&lt;</token>, <token>&gt;</token>,
                <token>|</token>, <token>;</token>, <token>&amp;</token>,
                <token>(</token> and <token>)</token>).
                Aside from delimiting words, spaces and tabs are ignored, while
                newlines usually delimit commands.
                The meta-characters are used in building the following tokens:
                <token>&lt;</token>, <token>&lt;&amp;</token>,
                <token>&lt;&lt;</token>, <token>&gt;</token>,
                <token>&gt;&amp;</token>, <token>&gt;&gt;</token>, etc. are
                used to specify redirections (see Input/Output Redirection below);
                <token>|</token> is used to create pipelines;
                <token>;</token> is used to separate commands;
                <token>&amp;</token> is used to create asynchronous pipelines;
                <token>&amp;&amp;</token> and <token>||</token> are used to specify conditional execution;
                <token>;;</token> is used in <token>case</token> statements;
                and lastly,
                <token>(</token> ... <token>)</token> are used to create subshells.</para>

            <para>White-space and meta-characters can be quoted individually using
                backslash (<emphasis remap='B'>&bsol;</emphasis>), or in groups using double (<emphasis remap='B'>"</emphasis>) or single (<emphasis remap='B'>'</emphasis>)
                quotes.
                Note that the following characters are also treated specially by the shell and
                must be quoted if they are to represent themselves:
                <emphasis remap='B'>&bsol;</emphasis>, <emphasis remap='B'>"</emphasis>, <emphasis remap='B'>'</emphasis>, <emphasis remap='B'>#</emphasis>, <emphasis remap='B'>$</emphasis>, <emphasis remap='B'>`</emphasis>, <emphasis remap='B'>~</emphasis>, <emphasis remap='B'>{</emphasis>,
                <emphasis remap='B'>}</emphasis>, <emphasis remap='B'>*</emphasis>, <emphasis remap='B'>?</emphasis> and <emphasis remap='B'>[</emphasis>.
                The first three of these are the above mentioned quoting characters
                (see Quoting below);
                <emphasis remap='B'>#</emphasis>, if used at the beginning of a word, introduces a comment &mdash; everything
                after the <emphasis remap='B'>#</emphasis> up to the nearest newline is ignored;
                <emphasis remap='B'>$</emphasis> is used to introduce parameter, command and arithmetic substitutions
                (see Substitution below);
                <emphasis remap='B'>`</emphasis> introduces an old-style command substitution
                (see Substitution below);
                <emphasis remap='B'>~</emphasis> begins a directory expansion (see Tilde Expansion below);
                <emphasis remap='B'>{</emphasis> and <emphasis remap='B'>}</emphasis> delimit <citerefentry><refentrytitle>csh</refentrytitle><manvolnum>1</manvolnum></citerefentry> style alternations
                (see Brace Expansion below);
                and, finally, <emphasis remap='B'>*</emphasis>, <emphasis remap='B'>?</emphasis> and <emphasis remap='B'>[</emphasis> are used in file name generation
                (see File Name Patterns below).</para>
            <!-- }}} -->
            <!-- {{{  simple\-command -->

            <para>As words and tokens are parsed, the shell builds commands, of which
                there are two basic types: <emphasis remap='I'>simple-commands</emphasis>, typically programs
                that are executed, and <emphasis remap='I'>compound-commands</emphasis>, such as <emphasis remap='B'>for</emphasis> and
                <emphasis remap='B'>if</emphasis> statements, grouping constructs and function definitions.</para>

            <para>A simple-command consists of some combination of parameter assignments (see
                Parameters below), input/output redirections (see Input/Output Redirections
                below), and command words; the only restriction is that parameter assignments
                come before any command words.
                The command words, if any, define the command that is to be executed and its
                arguments.
                The command may be a shell built-in command, a function or an <emphasis remap='I'>external
                    command</emphasis>, <emphasis remap='I'>i.e.</emphasis>, a separate executable file that is located using the
                <envar>PATH</envar> parameter (see Command Execution below).
                Note that all command constructs have an <emphasis remap='I'>exit status</emphasis>: for external
                commands, this is related to the status returned by <citerefentry><refentrytitle>wait</refentrytitle><manvolnum>2</manvolnum></citerefentry> (if the
                command could not be found, the exit status is 127, if it could not be
                executed, the exit status is 126);
                the exit status of other command constructs (built-in commands, functions,
                compound-commands, pipelines, lists, <emphasis remap='I'>etc.</emphasis>) are all well defined and are
                described where the construct is described.
                The exit status of a command consisting only of parameter assignments is that
                of the last command substitution performed during the parameter assignment
                or zero if there were no command substitutions.</para>
            <!-- }}} -->
            <!-- {{{  pipeline -->

            <para>Commands can be chained together using the <emphasis remap='B'>|</emphasis> token to
                form <emphasis remap='I'>pipelines</emphasis>, in which the standard output of each command but
                the last is piped (see <citerefentry><refentrytitle>pipe</refentrytitle><manvolnum>2</manvolnum></citerefentry>) to the standard input of the following
                command.
                The exit status of a pipeline is that of its last command.
                A pipeline may be prefixed by the <emphasis remap='B'>!</emphasis> reserved word which
                causes the exit status of the pipeline to be logically
                complemented: if the original status was 0 the complemented status will
                be 1, and if the original status was not 0, then the complemented
                status will be 0.</para>
            <!-- }}} -->
            <!-- {{{  lists -->

            <para><emphasis remap='I'>Lists</emphasis> of commands can be created by separating pipelines by
                any of the following tokens: <emphasis remap='B'>&amp;&amp;</emphasis>, <emphasis remap='B'>||</emphasis>, <emphasis remap='B'>&amp;</emphasis>, <emphasis remap='B'>|&amp;</emphasis> and <emphasis remap='B'>;</emphasis>.
                The first two are for conditional execution: <emphasis remap='I'>cmd1</emphasis> <emphasis remap='B'>&amp;&amp;</emphasis> <emphasis remap='I'>cmd2</emphasis>
                executes <emphasis remap='I'>cmd2</emphasis> only if the exit status of <emphasis remap='I'>cmd1</emphasis> is zero;
                <emphasis remap='B'>||</emphasis> is the opposite &mdash; <emphasis remap='I'>cmd2</emphasis> is executed only if the exit status
                of <emphasis remap='I'>cmd1</emphasis> is non-zero.
                <emphasis remap='B'>&amp;&amp;</emphasis> and <emphasis remap='B'>||</emphasis> have equal precedence which is higher than that of
                <emphasis remap='B'>&amp;</emphasis>, <emphasis remap='B'>|&amp;</emphasis> and <emphasis remap='B'>;</emphasis>, which also have equal precedence.
                The <emphasis remap='B'>&amp;</emphasis> token causes the preceding command to be executed asynchronously,
                that is, the shell starts the command, but does not wait for it to complete
                (the shell does keep track of the status of asynchronous commands &mdash; see
                Job Control below).
                When an asynchronous command is started when job control is disabled
                (<emphasis remap='I'>i.e.</emphasis>, in most scripts), the command is started with signals INT
                and QUIT ignored and with input redirected from /dev/null
                (however, redirections specified in the asynchronous command have precedence).
                Note that a command must follow the <emphasis remap='B'>&amp;&amp;</emphasis> and <emphasis remap='B'>||</emphasis> operators, while
                a command need not follow <emphasis remap='B'>&amp;</emphasis>, <emphasis remap='B'>|&amp;</emphasis> and <emphasis remap='B'>;</emphasis>.
                The exit status of a list is that of the last command executed, with the
                exception of asynchronous lists, for which the exit status is 0.</para>
            <!-- }}} -->
            <!-- {{{  compound\-commands -->

            <para>Compound commands are created using the following reserved words &mdash; these
                words are only recognized if they are unquoted and if they are used as
                the first word of a command (<emphasis remap='I'>i.e.</emphasis>, they can't be preceded by parameter
                assignments or redirections):</para>


            <informaltable pgwide='0' frame='none'>
                <tgroup cols='5' align='center'>
                    <colspec colname='c1'/>
                    <colspec colname='c2'/>
                    <colspec colname='c3'/>
                    <colspec colname='c4'/>
                    <colspec colname='c5'/>
                    <thead>
                        <row>
                            <entry align='center'>case</entry>
                            <entry align='right'>else</entry>
                        </row>
                    </thead>
                    <tbody>
                        <row>
                            <entry align='left'>do</entry>
                            <entry align='left'>esac</entry>
                            <entry align='left'>if</entry>
                            <entry align='left'>time</entry>
                            <entry align='left'>[[</entry>
                        </row>
                        <row>
                            <entry align='left'>done</entry>
                            <entry align='left'>fi</entry>
                            <entry align='left'>in</entry>
                            <entry align='left'>until</entry>
                            <entry align='left'>{</entry>
                        </row>
                        <row>
                            <entry align='left'>elif</entry>
                            <entry align='left'>for</entry>
                            <entry align='left'>select</entry>
                            <entry align='left'>while</entry>
                            <entry align='left'>}</entry>
                        </row>
                    </tbody>
                </tgroup>
            </informaltable>


            <para><emphasis remap='B'>Note:</emphasis> Some shells (but not this one) execute control structure commands
                in a subshell when one or more of their file descriptors are redirected, so
                any environment changes inside them may fail.
                To be portable, the <emphasis remap='B'>exec</emphasis> statement should be used instead to redirect
                file descriptors before the control structure.</para>

            <para>In the following compound command descriptions, command lists (denoted as
                <emphasis remap='I'>list</emphasis>) that are followed by reserved words must end with a
                semi-colon, a newline or a (syntactically correct) reserved word.
                For example,
                <!-- .RS -->
                <emphasis remap='B'>{ echo foo; echo bar; }</emphasis>
                <!-- .br -->
                <emphasis remap='B'>{ echo foo; echo bar&lt;newline&gt;}</emphasis>
                <!-- .br -->
                <emphasis remap='B'>{ { echo foo; echo bar; } }</emphasis>
                <!-- .RE -->
                are all valid, but
                <!-- .RS -->
                <emphasis remap='B'>{ echo foo; echo bar }</emphasis>
                <!-- .RE -->
                is not.</para>
            <!-- {{{  ( list ) -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term><emphasis remap='B'>(</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>)</emphasis></term>
                    <listitem>
                        <para>Execute <emphasis remap='I'>list</emphasis> in a subshell.  There is no implicit way to pass
                            environment changes from a subshell back to its parent.</para>
                        <!-- }}} -->
                        <!-- {{{  { list } -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>{</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>Compound construct; <emphasis remap='I'>list</emphasis> is executed, but not in a subshell.
                            Note that <emphasis remap='B'>{</emphasis> and <emphasis remap='B'>}</emphasis> are reserved words, not meta-characters.</para>
                        <!-- }}} -->
                        <!-- {{{  case word in [ [ ( ] pattern [ | pattern ] ... ) list ;; ] ... esac -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>case</emphasis> <emphasis remap='I'>word</emphasis> <emphasis remap='B'>in</emphasis> [ [<emphasis remap='B'>(</emphasis>] <emphasis remap='I'>pattern</emphasis> [<emphasis remap='B'>|</emphasis> <emphasis remap='I'>pattern</emphasis>] ... <emphasis remap='B'>)</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>;;</emphasis> ] ... <emphasis remap='B'>esac</emphasis></term>
                    <listitem>
                        <para>The <emphasis remap='B'>case</emphasis> statement attempts to match <emphasis remap='I'>word</emphasis> against the specified
                            <emphasis remap='I'>pattern</emphasis>s; the <emphasis remap='I'>list</emphasis> associated with the first successfully matched
                            pattern is executed.  Patterns used in <emphasis remap='B'>case</emphasis> statements are the same as
                            those used for file name patterns except that the restrictions regarding
                            <emphasis remap='B'>.</emphasis> and <emphasis remap='B'>/</emphasis> are dropped.  Note that any unquoted space before and
                            after a pattern is stripped; any space with a pattern must be quoted.  Both the
                            word and the patterns are subject to parameter, command, and arithmetic
                            substitution as well as tilde substitution.
                            For historical reasons, open and close braces may be used instead
                            of <emphasis remap='B'>in</emphasis> and <emphasis remap='B'>esac</emphasis> (<emphasis remap='I'>e.g.</emphasis>, <emphasis remap='B'>case $foo { *) echo bar; }</emphasis>).
                            The exit status of a <emphasis remap='B'>case</emphasis> statement is that of the executed <emphasis remap='I'>list</emphasis>;
                            if no <emphasis remap='I'>list</emphasis> is executed, the exit status is zero.</para>
                        <!-- }}} -->
                        <!-- {{{  for name [ in word ... term ] do list done -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>for</emphasis> <emphasis remap='I'>name</emphasis> [ <emphasis remap='B'>in</emphasis> <emphasis remap='I'>word</emphasis> ... <emphasis remap='I'>term</emphasis> ] <emphasis remap='B'>do</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>done</emphasis></term>
                    <listitem>
                        <para>where <emphasis remap='I'>term</emphasis> is either a newline or a <emphasis remap='B'>;</emphasis>.
                            For each <emphasis remap='I'>word</emphasis> in the specified word list, the parameter <emphasis remap='I'>name</emphasis> is
                            set to the word and <emphasis remap='I'>list</emphasis> is executed.  If <emphasis remap='B'>in</emphasis> is not used to
                            specify a word list, the positional parameters (<emphasis remap='B'>"$1"</emphasis>, <emphasis remap='B'>"$2"</emphasis>,
                            <emphasis remap='I'>etc.</emphasis>) are used instead.
                            For historical reasons, open and close braces may be used instead
                            of <emphasis remap='B'>do</emphasis> and <emphasis remap='B'>done</emphasis> (<emphasis remap='I'>e.g.</emphasis>, <emphasis remap='B'>for i; { echo $i; }</emphasis>).
                            The exit status of a <emphasis remap='B'>for</emphasis> statement is the last exit status
                            of <emphasis remap='I'>list</emphasis>; if <emphasis remap='I'>list</emphasis> is never executed, the exit status is zero.</para>
                        <!-- }}} -->
                        <!-- {{{  if list then list [ elif list then list ] ... [ else list ] fi -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>if</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>then</emphasis> <emphasis remap='I'>list</emphasis> [<emphasis remap='B'>elif</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>then</emphasis> <emphasis remap='I'>list</emphasis>] ... [<emphasis remap='B'>else</emphasis> <emphasis remap='I'>list</emphasis>] <emphasis remap='B'>fi</emphasis></term>
                    <listitem>
                        <para>If the exit status of the first <emphasis remap='I'>list</emphasis> is zero, the second <emphasis remap='I'>list</emphasis>
                            is executed; otherwise the <emphasis remap='I'>list</emphasis> following the <emphasis remap='B'>elif</emphasis>, if any, is
                            executed with similar consequences.  If all the lists following the <emphasis remap='B'>if</emphasis>
                            and <emphasis remap='B'>elif</emphasis>s fail (<emphasis remap='I'>i.e.</emphasis>, exit with non-zero status), the <emphasis remap='I'>list</emphasis>
                            following the <emphasis remap='B'>else</emphasis> is executed.
                            The exit status of an <emphasis remap='B'>if</emphasis> statement is that
                            of non-conditional <emphasis remap='I'>list</emphasis> that is executed; if no non-conditional
                            <emphasis remap='I'>list</emphasis> is executed, the exit status is zero.</para>
                        <!-- }}} -->
                        <!-- {{{  select name [ in word ... ] do list done -->
                        <!-- }}} -->
                        <!-- {{{  until list do list done -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>until</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>do</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>done</emphasis></term>
                    <listitem>
                        <para>This works like <emphasis remap='B'>while</emphasis>, except that the body is executed only while the
                            exit status of the first <emphasis remap='I'>list</emphasis> is non-zero.</para>
                        <!-- }}} -->
                        <!-- {{{  while list do list done -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>while</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>do</emphasis> <emphasis remap='I'>list</emphasis> <emphasis remap='B'>done</emphasis></term>
                    <listitem>
                        <para>A <emphasis remap='B'>while</emphasis> is a prechecked loop.  Its body is executed as often
                            as the exit status of the first <emphasis remap='I'>list</emphasis> is zero.
                            The exit status of a <emphasis remap='B'>while</emphasis> statement is the last exit status
                            of the <emphasis remap='I'>list</emphasis> in the body of the loop; if the body is not executed,
                            the exit status is zero.</para>
                    </listitem>
                </varlistentry>
                        <!-- }}} -->
                        <!-- {{{  name () command -->
                <varlistentry>
                    <term><emphasis remap='I'>name</emphasis> <emphasis remap='B'>()</emphasis> <emphasis remap='I'>command</emphasis></term>
                    <listitem>
                                <para>Defines the function <emphasis remap='I'>name</emphasis>.
                            See Functions below.
                            Note that redirections specified after a function definition are
                            performed whenever the function is executed, not when the function
                            definition is executed.</para>
                        <!-- {{{  time [\-p] [ pipeline ] -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>time</emphasis> [ <option>-p</option> ] [ <emphasis remap='I'>pipeline</emphasis> ]</term>
                    <listitem>
                        <para>The <emphasis remap='B'>time</emphasis> reserved word is described in the Command Execution section.</para>
                        <!-- }}} -->
                        <!-- {{{  (( expression )) -->
                        <!-- }}} -->
                        <!-- {{{  [[ expression ]] -->
                        <!-- }}} -->
                        <!-- }}} -->
                        <!-- }}} -->
                        <!-- {{{  Quoting -->
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->
        </refsect2>

        <refsect2 id='quoting'><title>Quoting</title>
            <para>Quoting is used to prevent the shell from treating characters or words
                specially.
                There are three methods of quoting: First, <emphasis remap='B'>&bsol;</emphasis> quotes
                the following character, unless it is at the end of a line, in which
                case both the <emphasis remap='B'>&bsol;</emphasis> and the newline are stripped.
                Second, a single quote (<emphasis remap='B'>'</emphasis>) quotes everything up to the next single
                quote (this may span lines).
                Third, a double quote (<emphasis remap='B'>"</emphasis>) quotes all characters,
                except <emphasis remap='B'>$</emphasis>, <emphasis remap='B'>`</emphasis> and <emphasis remap='B'>&bsol;</emphasis>, up to the next unquoted double quote.
                <emphasis remap='B'>$</emphasis> and <emphasis remap='B'>`</emphasis> inside double quotes have their usual meaning (<emphasis remap='I'>i.e.</emphasis>,
                parameter, command or arithmetic substitution) except no field splitting
                is carried out on the results of double-quoted substitutions.
                If a <emphasis remap='B'>&bsol;</emphasis> inside a double-quoted string is followed by <emphasis remap='B'>&bsol;</emphasis>, <emphasis remap='B'>$</emphasis>,
                <emphasis remap='B'>`</emphasis> or <emphasis remap='B'>"</emphasis>, it is replaced by the second character; if it is
                followed by a newline, both the <emphasis remap='B'>&bsol;</emphasis> and the newline are stripped;
                otherwise, both the <emphasis remap='B'>&bsol;</emphasis> and the character following are unchanged.</para>

            <para>Note: see POSIX Mode below for a special rule regarding sequences
                of the form <emphasis remap='B'>"</emphasis>...<emphasis remap='B'>`</emphasis>...<emphasis remap='B'>&bsol;"</emphasis>...<emphasis remap='B'>`</emphasis>..<emphasis remap='B'>"</emphasis>.</para>
            <!-- }}} -->
            <!-- {{{  Substitution -->
        </refsect2>

        <refsect2 id='substitution'><title>Substitution</title>
            <para>The first step the shell takes in executing a simple-command is to
                perform substitutions on the words of the command.
                There are three kinds of substitution: parameter, command and arithmetic.
                Parameter substitutions, which are described in detail in the next section,
                take the form <emphasis remap='B'>$name</emphasis> or <emphasis remap='B'>${</emphasis>...<emphasis remap='B'>}</emphasis>; command substitutions take
                the form <emphasis remap='B'>$(</emphasis><emphasis remap='I'>command</emphasis><emphasis remap='B'>)</emphasis> or <emphasis remap='B'>`</emphasis><emphasis remap='I'>command</emphasis><emphasis remap='B'>`</emphasis>;
                and arithmetic substitutions take the form <emphasis remap='B'>$((</emphasis><emphasis remap='I'>expression</emphasis><emphasis remap='B'>))</emphasis>.</para>

            <para>If a substitution appears outside of double quotes, the results of the
                substitution are generally subject to word or field splitting according to
                the current value of the <emphasis remap='B'>IFS</emphasis> parameter.
                The <emphasis remap='B'>IFS</emphasis> parameter specifies a list of characters which 
                are used to break a string up into several words;
                any characters from the set space, tab and newline that appear in the
                IFS characters are called <emphasis remap='I'>IFS white space</emphasis>.
                Sequences of one or more IFS white space characters, in combination with
                zero or one non-IFS white space characters delimit a field.
                As a special case, leading and trailing IFS white space is stripped (<emphasis remap='I'>i.e.</emphasis>,
                no leading or trailing empty field is created by it); leading or trailing
                non-IFS white space does create an empty field.
                Example: if <emphasis remap='B'>IFS</emphasis> is set to `&lt;space&gt;:', the sequence of characters
                `&lt;space&gt;A&lt;space&gt;:&lt;space&gt;&lt;space&gt;B::D' contains four fields: `A', `B', `' and `D'.
                Note that if the <emphasis remap='B'>IFS</emphasis> parameter is set to the null string, no
                field splitting is done; if the parameter is unset, the default value
                of space, tab and newline is used.</para>

            <para>The results of substitution are, unless otherwise specified, also subject
                to brace expansion and file name expansion (see the relevant sections
                below).</para>

            <para>A command substitution is replaced by the output generated by the specified
                command, which is run in a subshell.
                For <emphasis remap='B'>$(</emphasis><emphasis remap='I'>command</emphasis><emphasis remap='B'>)</emphasis> substitutions, normal quoting rules
                are used when <emphasis remap='I'>command</emphasis> is parsed, however, for the
                <emphasis remap='B'>`</emphasis><emphasis remap='I'>command</emphasis><emphasis remap='B'>`</emphasis> form, a <emphasis remap='B'>&bsol;</emphasis> followed by any of
                <emphasis remap='B'>$</emphasis>, <emphasis remap='B'>`</emphasis> or <emphasis remap='B'>&bsol;</emphasis> is stripped (a <emphasis remap='B'>&bsol;</emphasis> followed by any other
                character is unchanged).
                As a special case in command substitutions, a command of the form
                <emphasis remap='B'>&lt;</emphasis> <emphasis remap='I'>file</emphasis> is interpreted to mean substitute the contents
                of <emphasis remap='I'>file</emphasis> ($(&lt; foo) has the same effect as $(cat foo), but it
                is carried out more efficiently because no process is started).
                <!-- .br -->
                <!-- todo: fix this( $(..) parenthesis counting). -->
                NOTE: <emphasis remap='B'>$(</emphasis><emphasis remap='I'>command</emphasis><emphasis remap='B'>)</emphasis> expressions are currently parsed by
                finding the matching parenthesis, regardless of quoting.  This will hopefully
                be fixed soon.</para>

            <para>Arithmetic substitutions are replaced by the value of the specified
                expression.
                For example, the command <emphasis remap='B'>echo $((2+3*4))</emphasis> prints 14.
                See Arithmetic Expressions for a description of an <emphasis remap='I'>expression</emphasis>.</para>
            <!-- }}} -->
            <!-- {{{  Parameters -->
        </refsect2>

        <refsect2 id='parameters'><title>Parameters</title>
            <para>Parameters are shell variables; they can be assigned values and
                their values can be accessed using a parameter substitution.
                A parameter name is either one of the special single punctuation or digit
                character parameters described below, or a letter followed by zero or more
                letters or digits (`_' counts as a letter).
                The later form can be treated as arrays by appending an array
                index of the form: <emphasis remap='B'>[</emphasis><emphasis remap='I'>expr</emphasis><emphasis remap='B'>]</emphasis> where <emphasis remap='I'>expr</emphasis> is
                an arithmetic expression.
                Array indices are currently limited to the range 0 through 1023, inclusive.
                Parameter substitutions take the form <emphasis remap='B'>$</emphasis><emphasis remap='I'>name</emphasis>,
                <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>}</emphasis> or
                <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>[</emphasis><emphasis remap='I'>expr</emphasis><emphasis remap='B'>]}</emphasis>, where <emphasis remap='I'>name</emphasis> is a
                parameter name.
                If substitution is performed on a parameter (or an array parameter element)
                that is not set, a null
                string is substituted unless the <emphasis remap='B'>nounset</emphasis> option (<userinput>set -o nounset</userinput>
                or <userinput>set -u</userinput>) is set, in which case an error occurs.</para>

            <!-- {{{  parameter assignment -->
            <para>Parameters can be assigned values in a number of ways.
                First, the shell implicitly sets some parameters like <emphasis remap='B'>#</emphasis>, <envar>PWD</envar>,
                etc.; this is the only way the special single character parameters are
                set.
                Second, parameters are imported from the shell's environment at startup.
                Third, parameters can be assigned values on the command line, for example,
                `<emphasis remap='B'>FOO=bar</emphasis>' sets the parameter FOO to bar; multiple parameter
                assignments can be given on a single command line and they can
                be followed by a simple-command, in which case the assignments are
                in effect only for the duration of the command (such assignments are
                also exported, see below for implications of this).
                Note that both the parameter name and the <emphasis remap='B'>=</emphasis> must be unquoted for
                the shell to recognize a parameter assignment.
                The fourth way of setting a parameter is with the
                <emphasis remap='B'>export</emphasis> and
                <emphasis remap='B'>readonly</emphasis>
                commands; see their descriptions in the Command Execution
                section.
                Fifth, <emphasis remap='B'>for</emphasis> and <emphasis remap='B'>select</emphasis> loops set parameters as well as
                the <emphasis remap='B'>getopts</emphasis>, <emphasis remap='B'>read</emphasis> and <userinput>set -A</userinput> commands.
                Lastly, parameters can be assigned values using assignment operators
                inside arithmetic expressions (see Arithmetic Expressions below) or
                using the <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>=</emphasis><emphasis remap='I'>value</emphasis><emphasis remap='B'>}</emphasis> form
                of parameter substitution (see below).</para>
            <!-- }}} -->

            <!-- {{{  environment -->
            <para>Parameters with the export attribute (set using the <emphasis remap='B'>export</emphasis>
                command, or by parameter assignments followed by simple
                commands) are put in the environment (see <citerefentry><refentrytitle>environ</refentrytitle><manvolnum>5</manvolnum></citerefentry>) of commands
                run by the shell as <emphasis remap='I'>name</emphasis><emphasis remap='B'>=</emphasis><emphasis remap='I'>value</emphasis> pairs.
                The order in which parameters appear in the environment of a command
                is unspecified.
                When the shell starts up, it extracts parameters and their values from its
                environment and automatically sets the export attribute for those parameters.</para>
            <!-- }}} -->
            <!-- {{{  ${name[:][\-+=?]word} -->

            <para>Modifiers can be applied to the <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>}</emphasis> form of parameter
                substitution:</para>
            <variablelist remap='.IP'>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>:-</emphasis><emphasis remap='I'>word</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>if <emphasis remap='I'>name</emphasis> is set and not null, it is substituted, otherwise <emphasis remap='I'>word</emphasis> is
                            substituted.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>:+</emphasis><emphasis remap='I'>word</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>if <emphasis remap='I'>name</emphasis> is set and not null, <emphasis remap='I'>word</emphasis> is substituted, otherwise nothing is substituted.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>:=</emphasis><emphasis remap='I'>word</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>if <emphasis remap='I'>name</emphasis> is set and not null, it is substituted, otherwise it is
                            assigned <emphasis remap='I'>word</emphasis> and the resulting value of <emphasis remap='I'>name</emphasis> is substituted.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>:?</emphasis><emphasis remap='I'>word</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>if <emphasis remap='I'>name</emphasis> is set and not null, it is substituted, otherwise <emphasis remap='I'>word</emphasis>
                            is printed on standard error (preceded by <emphasis remap='I'>name</emphasis>:) and an error occurs
                            (normally causing termination of a shell script, function or .-script).
                            If word is omitted the string `parameter null or not set' is used instead.</para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>In the above modifiers, the <emphasis remap='B'>:</emphasis> can be omitted, in which case the
                conditions only depend on <emphasis remap='I'>name</emphasis> being set (as opposed to set and
                not null).
                If <emphasis remap='I'>word</emphasis> is needed, parameter, command, arithmetic and tilde substitution
                are performed on it; if <emphasis remap='I'>word</emphasis> is not needed, it is not evaluated.</para>
            <!-- }}} -->

            <para>The following forms of parameter substitution can also be used:</para>
            <!-- {{{  ${#name} -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term><emphasis remap='B'>${#</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>The number of positional parameters if <emphasis remap='I'>name</emphasis> is <emphasis remap='B'>*</emphasis>, <emphasis remap='B'>@</emphasis> or
                            is not specified,
                            or the length of the string value of parameter <emphasis remap='I'>name</emphasis>.</para>
                        <!-- }}} -->
                        <!-- {{{  ${#name[*]}, ${#name[@]} -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${#</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>[*]}</emphasis>, <emphasis remap='B'>${#</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>[@]}</emphasis></term>
                    <listitem>
                        <para>The number of elements in the array <emphasis remap='I'>name</emphasis>.</para>
                        <!-- }}} -->
                        <!-- {{{  ${name#pattern}, ${name##pattern} -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>#</emphasis><emphasis remap='I'>pattern</emphasis><emphasis remap='B'>}</emphasis>, <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>##</emphasis><emphasis remap='I'>pattern</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>If <emphasis remap='I'>pattern</emphasis> matches the beginning of the value of parameter <emphasis remap='I'>name</emphasis>,
                            the matched text is deleted from the result of substitution.  A single
                            <emphasis remap='B'>#</emphasis> results in the shortest match, two <emphasis remap='B'>#</emphasis>'s results in the
                            longest match.</para>
                        <!-- }}} -->
                        <!-- {{{  ${name%pattern}, ${name%%pattern} -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>%</emphasis><emphasis remap='I'>pattern</emphasis><emphasis remap='B'>}</emphasis>, <emphasis remap='B'>${</emphasis><emphasis remap='I'>name</emphasis><emphasis remap='B'>%%</emphasis><emphasis remap='I'>pattern</emphasis><emphasis remap='B'>}</emphasis></term>
                    <listitem>
                        <para>Like <emphasis remap='B'>${</emphasis>..<emphasis remap='B'>#</emphasis>..<emphasis remap='B'>}</emphasis> substitution, but it deletes from the end of the
                            value.</para>
                        <!-- }}} -->
                        <!-- {{{  special shell parameters -->
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>The following special parameters are implicitly set by the shell and cannot be
                set directly using assignments:</para>
            <!-- {{{  ! -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term><emphasis remap='B'>!</emphasis></term>
                    <listitem>
                        <para>Process id of the last background process started.  If no background
                            processes have been started, the parameter is not set.</para>
                        <!-- }}} -->
                        <!-- {{{  # -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>#</emphasis></term>
                    <listitem>
                        <para>The number of positional parameters (<emphasis remap='I'>i.e.</emphasis>, <emphasis remap='B'>$1</emphasis>, <emphasis remap='B'>$2</emphasis>,
                            <emphasis remap='I'>etc.</emphasis>).</para>
                        <!-- }}} -->
                        <!-- {{{  $ -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>$</emphasis></term>
                    <listitem>
                        <para>The process ID of the shell, or the PID of the original shell if
                            it is a subshell.</para>
                        <!-- }}} -->
                        <!-- {{{  \- -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>-</emphasis></term>
                    <listitem>
                        <para>The concatenation of the current single letter options
                            (see <emphasis remap='B'>set</emphasis> command below for list of options).</para>
                        <!-- }}} -->
                        <!-- {{{  ? -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>?</emphasis></term>
                    <listitem>
                        <para>The exit status of the last non-asynchronous command executed.
                            If the last command was killed by a signal, <emphasis remap='B'>$?</emphasis> is set to 128 plus
                            the signal number.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><varname>0</varname></term>
                    <listitem>
                            <para>The name the shell was invoked with (that is,
                                    <varname>argv[0]</varname>), or the
                                    <command><replaceable>command-name</replaceable></command>
                                    if it was invoked with the <option>-c</option>
                                    option and the
                                    <command><replaceable>command-name</replaceable></command>
                    was supplied, or the
                    <filename><replaceable>file</replaceable></filename> argument, if it was
                            supplied.
                            If the <option>posix</option> option is not set, <emphasis remap='B'>$0</emphasis> is the name of the current
                            function or script.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><varname>1</varname> ... <varname>9</varname></term>
                    <listitem>
                        <para>The first nine positional parameters that were supplied to the shell,
                            function or <command>.</command>-script.
                            Further positional parameters may be accessed using
                            <varname>${<replaceable>number</replaceable>}</varname>.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><varname>*</varname></term>
                    <listitem>
                        <para>All positional parameters (except parameter 0), 
                            <emphasis remap='I'>i.e.</emphasis>, <emphasis remap='B'>$1 $2 $3</emphasis>....
                            If used outside of double quotes, parameters are separate words
                            (which are subjected to word splitting); if used within double quotes,
                            parameters are separated by the first character of the <emphasis remap='B'>IFS</emphasis> parameter
                            (or the empty string if <emphasis remap='B'>IFS</emphasis> is null).</para>
                        <!-- }}} -->
                        <!-- {{{  @ -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><varname>@</varname></term>
                    <listitem>
                        <para>Same as <emphasis remap='B'>$*</emphasis>, unless it is used inside double quotes, in which case
                            a separate word is generated for each positional parameter - if there
                            are no positional parameters, no word is generated ("$@" can be used
                            to access arguments, verbatim, without loosing null arguments or
                            splitting arguments with spaces).</para>
                        <!-- }}} -->
                        <!-- }}} -->
                        <!-- {{{  general shell parameters -->
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>The following parameters are set and/or used by the shell:</para>
            <!-- {{{  _ -->
            <!-- }}} -->
            <!-- {{{  CDPATH -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"<emphasis remap='B'>CDPATH</emphasis>"</term>
                    <listitem>
                        <para>Search path for the <emphasis remap='B'>cd</emphasis> built-in command.  Works the same way as
                            <envar>PATH</envar> for those directories not beginning with <emphasis remap='B'>/</emphasis> in <emphasis remap='B'>cd</emphasis>
                            commands.
                            Note that if CDPATH is set and does not contain <literal>.</literal> nor an empty path,
                            the current directory is not searched.</para>
                        <!-- }}} -->
                        <!-- {{{  COLUMNS -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>COLUMNS</envar></term>
                    <listitem>
                        <para>Set to the number of columns on the terminal or window.
                            Currently set to the <emphasis remap='B'>cols</emphasis> value as reported by <citerefentry><refentrytitle>stty</refentrytitle><manvolnum>1</manvolnum></citerefentry> if that
                            value is non-zero.
                            This parameter is used by the interactive line editing modes, and by
                            <emphasis remap='B'>select</emphasis>, <userinput>set -o</userinput> and <userinput>kill -l</userinput> commands
                            to format information in columns.</para>
                        <!-- }}} -->
                        <!-- {{{  EDITOR -->
                        <!-- }}} -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>ERRNO</emphasis></term>
                    <listitem>
                        <para>Integer value of the shell's errno variable &mdash; indicates the reason
                            the last system call failed.</para>
                        <!--  todo: ERRNO variable -->

                        <para>Not implemented yet.</para>
                        <!-- }}} -->
                        <!-- {{{  EXECSHELL -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>EXECSHELL</emphasis></term>
                    <listitem>
                        <para>If set, this parameter is assumed to contain the shell that is to be
                            used to execute commands that <citerefentry><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry> fails to execute and
                            which do not start with a `<emphasis remap='B'>#!</emphasis> <emphasis remap='I'>shell</emphasis>' sequence.</para>
                        <!-- }}} -->
                        <!-- {{{  FCEDIT -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>FCEDIT</emphasis></term>
                    <listitem>
                        <para>The editor used by the <emphasis remap='B'>fc</emphasis> command (see below).</para>
                        <!-- }}} -->
                        <!-- {{{  FPATH -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>FPATH</emphasis></term>
                    <listitem>
                        <para>Like <envar>PATH</envar>, but used when an undefined function is executed to locate
                            the file defining the function.
                            It is also searched when a command can't be found using <envar>PATH</envar>.
                            See Functions below for more information.</para>
                        <!-- }}} -->
                        <!-- {{{  HISTFILE -->
                        <!-- }}} -->
                        <!-- {{{  HISTSIZE -->
                        <!-- }}} -->
                        <!-- {{{  HOME -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>HOME</envar></term>
                    <listitem>
                        <para>The default directory for the <emphasis remap='B'>cd</emphasis> command and the value
                            substituted for an unqualified <emphasis remap='B'>~</emphasis> (see Tilde Expansion below).</para>
                        <!-- }}} -->
                        <!-- {{{  IFS -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>IFS</emphasis></term>
                    <listitem>
                        <para>Internal field separator, used during substitution and by the <emphasis remap='B'>read</emphasis>
                            command, to split values into distinct arguments; normally set to
                            space, tab and newline.  See Substitution above for details.
                            <!-- .br -->
                            <emphasis remap='B'>Note:</emphasis> this parameter is not imported from the environment
                            when the shell is started.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>POSH_VERSION</emphasis></term>
                    <listitem>
                        <para>The version of posh (readonly).</para>
                        <!-- }}} -->
                        <!-- {{{  LINENO -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>LINENO</emphasis></term>
                    <listitem>
                        <para>The line number of the function or shell script that is currently being
                            executed.</para>
                        <!-- }}} -->
                        <!-- {{{  LINES -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>LINES</envar></term>
                    <listitem>
                        <para>Set to the number of lines on the terminal or window.</para>
                        <!-- Currently set to the \fBrows\fP value as reported by \fIstty\fP(1) if that -->
                        <!-- value is non\-zero. -->
                        <!--  todo: LINES variable -->

                        <para>Not implemented yet.</para>
                        <!-- }}} -->
                        <!-- {{{  MAIL -->
                        <!-- }}} -->
                        <!-- {{{  MAILCHECK -->
                        <!-- }}} -->
                        <!-- {{{  MAILPATH -->
                        <!-- }}} -->
                        <!-- {{{  OLDPWD -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>OLDPWD</envar></term>
                    <listitem>
                        <para>The previous working directory.
                            Unset if <emphasis remap='B'>cd</emphasis> has not successfully changed directories since the
                            shell started, or if the shell doesn't know where it is.</para>
                        <!-- }}} -->
                        <!-- {{{  OPTARG -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>OPTARG</envar></term>
                    <listitem>
                        <para>When using <emphasis remap='B'>getopts</emphasis>, it contains the argument for a parsed option,
                            if it requires one.</para>
                        <!-- }}} -->
                        <!-- {{{  OPTIND -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>OPTIND</envar></term>
                    <listitem>
                        <para>The index of the last argument processed when using <emphasis remap='B'>getopts</emphasis>.
                            Assigning 1 to this parameter causes <emphasis remap='B'>getopts</emphasis> to
                            process arguments from the beginning the next time it is invoked.</para>
                        <!-- }}} -->
                        <!-- {{{  PATH -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PATH</envar></term>
                    <listitem>
                        <para>A colon separated list of directories that are searched when looking
                            for commands and <literal>.</literal>'d files.
                            An empty string resulting from a leading or trailing colon, or two adjacent
                            colons is treated as a `.', the current directory.</para>
                        <!-- }}} -->
                        <!-- {{{  PPID -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PPID</envar></term>
                    <listitem>
                        <para>The process ID of the shell's parent (readonly).</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PS1</envar></term>
                    <listitem>
                        <para>The primary prompt for interactive shells.
                            The prompt is printed verbatim (<emphasis remap='I'>i.e.</emphasis>, no substitutions are done).
                            Default is
                            &lsquo;<literal>$&nbsp;</literal>&rsquo; for non-root users, `<emphasis remap='B'>#&nbsp;</emphasis>' for root..</para>
                        <!-- }}} -->
                        <!-- {{{  PS2 -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PS2</envar></term>
                    <listitem>
                        <para>Secondary prompt string, by default `<emphasis remap='B'>&gt;</emphasis> ', used when more input is
                            needed to complete a command.</para>
                        <!-- }}} -->
                        <!-- {{{  PS3 -->
                        <!-- }}} -->
                        <!-- {{{  PS4 -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PS4</envar></term>
                    <listitem>
                        <para>Used to prefix commands that are printed during execution tracing
                            (see <userinput>set -x</userinput> command below).
                            The prompt is printed verbatim (<emphasis remap='I'>i.e.</emphasis>, no substitutions are done).
                            Default is `<emphasis remap='B'>+&nbsp;</emphasis>'.</para>
                        <!-- }}} -->
                        <!-- {{{  PWD -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>PWD</envar></term>
                    <listitem>
                        <para>The current working directory.  Maybe unset or null if shell doesn't
                            know where it is.</para>
                        <!-- }}} -->
                        <!-- {{{  RANDOM -->
                        <!-- }}} -->
                        <!-- {{{  REPLY -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>REPLY</emphasis></term>
                    <listitem>
                        <para>Default parameter for the <emphasis remap='B'>read</emphasis> command if no names are given.
                            Also used in <emphasis remap='B'>select</emphasis> loops to store the value that is read from
                            standard input.</para>
                        <!-- }}} -->
                        <!-- {{{  SECONDS -->
                        <!-- }}} -->
                        <!-- {{{  TMOUT -->
                        <!-- }}} -->
                        <!-- {{{  TMPDIR -->
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><envar>TMPDIR</envar></term>
                    <listitem>
                        <para>The directory shell temporary files are created in.  If this parameter
                            is not set, or does not contain the absolute path of a writable
                            directory, temporary files are created in <filename>/tmp</filename>.</para>
                        <!-- }}} -->
                        <!-- {{{  VISUAL -->
                        <!-- }}} -->
                        <!-- }}} -->
                        <!-- }}} -->
                        <!-- {{{  Tilde Expansion -->
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->
        </refsect2>

        <refsect2 id='tilde_expansion'><title>Tilde Expansion</title>
            <para>Tilde expansion, which is done in parallel with parameter substitution,
                is done on words starting with an unquoted <emphasis remap='B'>~</emphasis>.  The characters
                following the tilde, up to the first <emphasis remap='B'>/</emphasis>, if any, are assumed to be
                a login name.  If the login name is empty, <emphasis remap='B'>+</emphasis> or <emphasis remap='B'>-</emphasis>, the
                value of the <envar>HOME</envar>, <envar>PWD</envar>, or <emphasis remap='B'>OLDPWD</emphasis> parameter is
                substituted, respectively.  Otherwise, the password file is searched for
                the login name, and the tilde expression is substituted with the
                user's home directory.  If the login name is not found in the password
                file or if any quoting or parameter substitution occurs in the login name,
                no substitution is performed.</para>

            <para>In parameter assignments (those preceding a simple-command or those
                    occurring in the arguments of <emphasis remap='B'>alias</emphasis>, <emphasis remap='B'>export</emphasis>,
                   and <emphasis remap='B'>readonly</emphasis>,
                tilde expansion is done after any unquoted colon
                (<emphasis remap='B'>:</emphasis>), and login names are also delimited by colons.</para>

            <para>The home directory of previously expanded login names are cached and
                re-used.  The <userinput>alias -d</userinput> command may be used to list, change and
                add to this cache (<emphasis remap='I'>e.g.</emphasis>, `alias -d fac=/usr/local/facilities; cd
                ~fac/bin').</para>
            <!-- }}} -->
            <!-- {{{  Brace Expansion -->
            <!-- }}} -->
            <!-- {{{  File Name Patterns -->
        </refsect2>

        <refsect2 id='file_name_patterns'><title>File Name Patterns</title>

            <para>A file name pattern is a word containing one or more unquoted <emphasis remap='B'>?</emphasis> or
                <emphasis remap='B'>*</emphasis> characters or <emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis> sequences.  Once brace expansion has
                been performed, the shell replaces file name patterns with the sorted names
                of all the files that match the pattern (if no files match, the word is
                left unchanged).  The pattern elements have the following meaning:</para>
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"<emphasis remap='B'>?</emphasis>"</term>
                    <listitem>
                        <para>matches any single character.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>*</emphasis></term>
                    <listitem>
                        <para>matches any sequence of characters.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis></term>
                    <listitem>
                        <para>matches any of the characters inside the brackets.  Ranges of characters
                            can be specified by separating two characters by a <emphasis remap='B'>-</emphasis>, <emphasis remap='I'>e.g.</emphasis>,
                            <emphasis remap='B'>[a0-9]</emphasis> matches the letter <emphasis remap='B'>a</emphasis> or any digit.
                            In order to represent itself, a
                            <emphasis remap='B'>-</emphasis> must either be quoted or the first or last character in the character
                            list.  Similarly, a <emphasis remap='B'>]</emphasis> must be quoted or the first character in the list
                            if it is represent itself instead of the end of the list.  Also, a <emphasis remap='B'>!</emphasis>
                            appearing at the start of the list has special meaning (see below), so to
                            represent itself it must be quoted or appear later in the list.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><emphasis remap='B'>[!</emphasis>..<emphasis remap='B'>]</emphasis></term>
                    <listitem>
                        <para>like <emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis>, except it matches any character not inside the brackets.</para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>Note that posh currently never matches <literal>.</literal> and <literal>..</literal>, but the original
                ksh, Bourne sh and bash do, so this may have to change (too bad).</para>

            <para>Note that none of the above pattern elements match either a period (<literal>.</literal>)
                at the start of a file name or a slash (<emphasis remap='B'>/</emphasis>), even if they are explicitly
                used in a <emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis> sequence; also, the names <literal>.</literal> and <literal>..</literal>
                are never matched, even by the pattern <emphasis remap='B'>.*</emphasis>.</para>

            <!--  todo: implement this ([[:alpha:]], \fIetc.\fP) -->
            <para>The POSIX character classes (<emphasis remap='I'>i.e.</emphasis>,
                <emphasis remap='B'>[:</emphasis><emphasis remap='I'>class-name</emphasis><emphasis remap='B'>:]</emphasis> inside a <emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis> expression)
                are not yet implemented.</para>
            <!-- }}} -->
            <!-- {{{  Input/Output Redirection -->
        </refsect2>

        <refsect2 id='inputoutput_redirection'><title>Input/Output Redirection</title>
            <para>When a command is executed, its standard input, standard output and
                standard error (file descriptors 0, 1 and 2, respectively) are normally
                inherited from the shell.
                Three exceptions to this are commands in pipelines, for which standard input
                and/or standard output are those set up by the pipeline, asynchronous commands
                created when job control is disabled, for which standard input is initially
                set to be from <filename>/dev/null</filename>, and commands for which any of the following
                redirections have been specified:</para>
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"<emphasis remap='B'>&gt;</emphasis> <emphasis remap='I'>file</emphasis>"</term>
                    <listitem>
                        <para>standard output is redirected to <emphasis remap='I'>file</emphasis>.  If <emphasis remap='I'>file</emphasis> does not exist,
                            it is created; if it does exist, is a regular file and the <emphasis remap='B'>noclobber</emphasis>
                            option is set, an error occurs, otherwise the file is truncated.
                            Note that this means the command <emphasis remap='I'>cmd &lt; foo &gt; foo</emphasis> will open
                            <emphasis remap='I'>foo</emphasis> for reading and then truncate it when it opens it for writing,
                            before <emphasis remap='I'>cmd</emphasis> gets a chance to actually read <emphasis remap='I'>foo</emphasis>.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&gt;|</emphasis> <emphasis remap='I'>file</emphasis>"</term>
                    <listitem>
                        <para>same as <emphasis remap='B'>&gt;</emphasis>, except the file is truncated, even if the <emphasis remap='B'>noclobber</emphasis>
                            option is set.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&gt;&gt;</emphasis> <emphasis remap='I'>file</emphasis>"</term>
                    <listitem>
                        <para>same as <emphasis remap='B'>&gt;</emphasis>, except the file an existing file is appended to instead
                            of being truncated.  Also, the file is opened in append mode, so writes
                            always go to the end of the file (see <citerefentry><refentrytitle>open</refentrytitle><manvolnum>2</manvolnum></citerefentry>).</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;</emphasis> <emphasis remap='I'>file</emphasis>"</term>
                    <listitem>
                        <para>standard input is redirected from <emphasis remap='I'>file</emphasis>, which is opened for reading.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;&gt;</emphasis> <emphasis remap='I'>file</emphasis>"</term>
                    <listitem>
                        <para>same as <emphasis remap='B'>&lt;</emphasis>, except the file is opened for reading and writing.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;&lt;</emphasis> <emphasis remap='I'>marker</emphasis>"</term>
                    <listitem>
                        <para>after reading the command line containing this kind of redirection (called a
                            here document), the shell copies lines from the command source into a temporary
                            file until a line matching <emphasis remap='I'>marker</emphasis> is read.
                            When the command is executed, standard input is redirected from the temporary
                            file.
                            If <emphasis remap='I'>marker</emphasis> contains no quoted characters, the contents of the
                            temporary file are processed as if enclosed in double quotes each time
                            the command is executed, so parameter, command and arithmetic substitutions
                            are performed, along with backslash (<emphasis remap='B'>&bsol;</emphasis>) escapes for
                            <emphasis remap='B'>$</emphasis>, <emphasis remap='B'>`</emphasis>, <emphasis remap='B'>&bsol;</emphasis> and <emphasis remap='B'>&bsol;newline</emphasis>.
                            If multiple here documents are used on the same command line, they are
                            saved in order.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;&lt;-</emphasis> <emphasis remap='I'>marker</emphasis>"</term>
                    <listitem>
                        <para>same as <emphasis remap='B'>&lt;&lt;</emphasis>, except leading tabs are stripped from lines in the
                            here document.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;&amp;</emphasis> <emphasis remap='I'>fd</emphasis>"</term>
                    <listitem>
                        <para>standard input is duplicated from file descriptor <emphasis remap='I'>fd</emphasis>.
                            <emphasis remap='I'>fd</emphasis> can be a single digit, indicating the number of an existing
                            file descriptor, the letter <emphasis remap='B'>p</emphasis>, indicating the file descriptor
                            associated with the output of the current co-process, or
                            the character <emphasis remap='B'>-</emphasis>, indicating standard input is to be closed.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&gt;&amp;</emphasis> <emphasis remap='I'>fd</emphasis>"</term>
                    <listitem>
                        <para>same as <emphasis remap='B'>&lt;&amp;</emphasis>, except the operation is done on standard output.</para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>In any of the above redirections, the file descriptor that is redirected
                (<emphasis remap='I'>i.e.</emphasis>, standard input or standard output) can be explicitly given by
                preceding the redirection with a single digit.
                Parameter, command and arithmetic substitutions, tilde substitutions and
                (if the shell is interactive) file name generation are all performed
                on the <emphasis remap='I'>file</emphasis>, <emphasis remap='I'>marker</emphasis> and <emphasis remap='I'>fd</emphasis> arguments of redirections.
                Note however, that the results of any file name generation are only used
                if a single file is matched; if multiple files match, the word with the
                unexpanded file name generation characters is used.</para>

            <para>For simple-commands, redirections may appear anywhere in the command, for
                compound-commands (<emphasis remap='B'>if</emphasis> statements, <emphasis remap='I'>etc.</emphasis>), any redirections must
                appear at the end.
                Redirections are processed after pipelines are created and in the order they
                are given, so
                <!-- .RS -->
                <emphasis remap='B'>cat /foo/bar 2&gt;&amp;1 &gt; /dev/null | cat -n</emphasis>
                <!-- .RE -->
                will print an error with a line number prepended to it.</para>
            <!-- }}} -->
            <!-- {{{  Arithmetic Expressions -->
        </refsect2>

        <refsect2 id='arithmetic_expressions'><title>Arithmetic Expressions</title>
            <para>Integer arithmetic expressions can be used
                inside <emphasis remap='B'>$((</emphasis>..<emphasis remap='B'>))</emphasis> expressions,
                inside array references (<emphasis remap='I'>e.g.</emphasis>, <emphasis remap='I'>name</emphasis><emphasis remap='B'>[</emphasis><emphasis remap='I'>expr</emphasis><emphasis remap='B'>]</emphasis>),
                as numeric arguments to the <emphasis remap='B'>test</emphasis> command,
                and as the value of an assignment to an integer parameter.</para>

            <para>Expression may contain alpha-numeric parameter identifiers, array
                references, and integer constants and may be combined with the
                following C operators (listed and grouped in increasing order of precedence).</para>
            <variablelist remap='TP'>
                <varlistentry>
                    <term>Unary operators:</term>
                    <listitem>
                        <para><emphasis remap='B'>+ - ! ~ ++ --</emphasis></para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Binary operators:</term>
                    <listitem>
                        <para><emphasis remap='B'>,</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>= *= /= %= += -= &lt;&lt;= &gt;&gt;= &amp;= ^= |=</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>||</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>&amp;&amp;</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>|</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>^</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>&amp;</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>== !=</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>&lt; &lt;= &gt;= &gt;</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>&lt;&lt; &gt;&gt;</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>+ -</emphasis>
                            <!-- .br -->
                            <emphasis remap='B'>* / %</emphasis></para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Ternary operator:</term>
                    <listitem>
                        <para><emphasis remap='B'>?:</emphasis> (precedence is immediately higher than assignment)</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Grouping operators:</term>
                    <listitem>
                        <para><emphasis remap='B'>( )</emphasis></para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .TP -->

            <para>Integer constants may be specified with arbitrary bases using the notation
                <emphasis remap='I'>base</emphasis><emphasis remap='B'>#</emphasis><emphasis remap='I'>number</emphasis>, where <emphasis remap='I'>base</emphasis> is a decimal integer specifying
                the base, and <emphasis remap='I'>number</emphasis> is a number in the specified base.</para>

            <para>The operators are evaluated as follows:</para>
            <!-- .RS -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"unary <emphasis remap='B'>+</emphasis>"</term>
                    <listitem>
                        <para>result is the argument (included for completeness).</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"unary <emphasis remap='B'>-</emphasis>"</term>
                    <listitem>
                        <para>negation.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>!</emphasis>"</term>
                    <listitem>
                        <para>logical not; the result is 1 if argument is zero, 0 if not.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>~</emphasis>"</term>
                    <listitem>
                        <para>arithmetic (bit-wise) not.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>++</emphasis>"</term>
                    <listitem>
                        <para>increment; must be applied to a parameter (not a literal or other
                            expression) - the parameter is incremented by 1.
                            When used as a prefix operator, the result is the incremented value of
                            the parameter, when used as a postfix operator, the result is the
                            original value of the parameter.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>++</emphasis>"</term>
                    <listitem>
                        <para>similar to <emphasis remap='B'>++</emphasis>,
                                except the parameter is decremented by 1.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>,</emphasis>"</term>
                    <listitem>
                        <para>separates two arithmetic expressions; the left hand side is evaluated first,
                            then the right.  The result is value of the expression on the right hand side.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>=</emphasis>"</term>
                    <listitem>
                        <para>assignment; variable on the left is set to the value on the right.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>*= /= %= += -= &lt;&lt;= &gt;&gt;= &amp;= ^= |=</emphasis>"</term>
                    <listitem>
                        <para>assignment operators; <emphasis remap='I'>&lt;var&gt; &lt;op&gt;</emphasis><emphasis remap='B'>=</emphasis> <emphasis remap='I'>&lt;expr&gt;</emphasis> is the same as
                            <emphasis remap='I'>&lt;var&gt;</emphasis> <emphasis remap='B'>=</emphasis> <emphasis remap='I'>&lt;var&gt; &lt;op&gt;</emphasis> <emphasis remap='B'>(</emphasis> <emphasis remap='I'>&lt;expr&gt;</emphasis> <emphasis remap='B'>)</emphasis>.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>||</emphasis>"</term>
                    <listitem>
                        <para>logical or; the result is 1 if either argument is non-zero, 0 if not.
                            The right argument is evaluated only if the left argument is zero.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&amp;&amp;</emphasis>"</term>
                    <listitem>
                        <para>logical and; the result is 1 if both arguments are non-zero, 0 if not.
                            The right argument is evaluated only if the left argument is non-zero.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>|</emphasis>"</term>
                    <listitem>
                        <para>arithmetic (bit-wise) or.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>^</emphasis>"</term>
                    <listitem>
                        <para>arithmetic (bit-wise) exclusive-or.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&amp;</emphasis>"</term>
                    <listitem>
                        <para>arithmetic (bit-wise) and.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>==</emphasis>"</term>
                    <listitem>
                        <para>equal; the result is 1 if both arguments are equal, 0 if not.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>!=</emphasis>"</term>
                    <listitem>
                        <para>not equal; the result is 0 if both arguments are equal, 1 if not.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;</emphasis>"</term>
                    <listitem>
                        <para>less than; the result is 1 if the left argument is less than the right,
                            0 if not.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;= &gt;= &gt;</emphasis>"</term>
                    <listitem>
                        <para>less than or equal, greater than or equal, greater than.  See &lt;.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>&lt;&lt; &gt;&gt;</emphasis>"</term>
                    <listitem>
                        <para>shift left (right); the result is the left argument with its bits shifted
                            left (right) by the amount given in the right argument.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>+ - * /</emphasis>"</term>
                    <listitem>
                        <para>addition, subtraction, multiplication, and division.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>%</emphasis>"</term>
                    <listitem>
                        <para>remainder; the result is the remainder of the division of the left argument
                            by the right.  The sign of the result is unspecified if either argument
                            is negative.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='I'>&lt;arg1&gt;</emphasis> <emphasis remap='B'>?</emphasis> <emphasis remap='I'>&lt;arg2&gt;</emphasis> <emphasis remap='B'>:</emphasis> <emphasis remap='I'>&lt;arg3&gt;</emphasis>"</term>
                    <listitem>
                        <para>if <emphasis remap='I'>&lt;arg1&gt;</emphasis> is non-zero, the result is <emphasis remap='I'>&lt;arg2&gt;</emphasis>,
                            otherwise <emphasis remap='I'>&lt;arg3&gt;</emphasis>.</para>
                        <!-- .RE -->
                        <!-- }}} -->
                        <!-- {{{  Co\-Processes -->
                        <!-- }}} -->
                        <!-- {{{  Functions -->
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->
        </refsect2>

        <refsect2 id='functions'><title>Functions</title>
            <para>
                Functions are defined using the Bourne/POSIX shell
                <emphasis remap='I'>name</emphasis><emphasis
                        remap='B'>()</emphasis> syntax.
                Functions are like <literal>.</literal>-scripts in that they are executed in
                the current environment, however, unlike <literal>.</literal>-scripts, shell arguments
                (<emphasis remap='I'>i.e.</emphasis>, positional parameters, <emphasis remap='B'>$1</emphasis>, <emphasis remap='I'>etc.</emphasis>) are never visible
                inside them.
                When the shell is determining the location of a command, functions are
                searched after special built-in commands, and before regular and non-regular
                built-ins, and before the <envar>PATH</envar> is searched.
            </para>

            <para>
                An existing function may be deleted using <userinput>unset -f</userinput> <emphasis remap='I'>function-name</emphasis>.
            </para>

            <para>
                Since functions are executed in the current shell environment, parameter
                assignments made inside functions are visible after the function completes.
            </para>

            <para>
                The exit status of a function is that of the last command
                executed in the function.  A function can be made to finish
                immediately using the <emphasis remap='B'>return</emphasis>
                command; this may also be used to explicitly specify the
                exit status.
            </para>

        </refsect2>
        <refsect2 id='command_execution'>
            <title>Command Execution</title>
            <para>
                After evaluation of command line arguments, redirections and
                parameter assignments, the type of command is determined: a
                special built-in, a function, a regular built-in or the name
                of a file to execute found using the <envar>PATH</envar>
                parameter.  The checks are made in the above order.
                Special built-in commands differ from other commands in that 
                the <envar>PATH</envar> parameter is not used to find them,
                an error during their execution can cause a non-interactive
                shell to exit and parameter assignments that are specified
                before the command are kept after the command completes.
                Just to confuse things, if the posix option is turned off
                (see <command>set</command> command below) some
                special commands are very special in that no field splitting,
                file globbing, brace expansion nor tilde expansion is performed
                on arguments that look like assignments.  Regular built-in
                commands are different only in that the <envar>PATH</envar>
                parameter is not used to find them.
            </para>

        </refsect2>
        <refsect2 id='job_control'><title>Job Control</title>
            <para>Job control refers to the shell's ability to monitor and control <emphasis remap='B'>jobs</emphasis>,
                which are processes or groups of processes created for commands or pipelines.
                At a minimum, the shell keeps track of the status of the background
                (<emphasis remap='I'>i.e.</emphasis>, asynchronous) jobs that currently exist; this information can be
                displayed using the <command>jobs</command> command.
                If job control is fully enabled (using <userinput>set -m</userinput> or
                <userinput>set -o monitor</userinput>), as it is for interactive shells,
                the processes of a job are placed in their own process group,
                foreground jobs can be stopped by typing the suspend character from the
                terminal (normally ^Z),
                jobs can be restarted in either the foreground
                or background, using the <command>fg</command>
                and <command>bg</command> commands, respectively,
                and the state of the terminal is saved or restored when a foreground
                job is stopped or restarted, respectively.
            </para>

            <para>Note that only commands that create processes (<emphasis remap='I'>e.g.</emphasis>,
                asynchronous commands, subshell commands, and non-built-in,
                non-function commands) can be stopped; commands like <emphasis remap='B'>read</emphasis> cannot be.
            </para>

            <para>When a job is created, it is assigned a job-number.
                For interactive shells, this number is printed inside <emphasis remap='B'>[</emphasis>..<emphasis remap='B'>]</emphasis>,
                followed by the process-ids of the processes in the job when an asynchronous
                command is run.
                A job may be referred to in <emphasis remap='B'>bg</emphasis>, <emphasis remap='B'>fg</emphasis>, <emphasis remap='B'>jobs</emphasis>, <emphasis remap='B'>kill</emphasis> and
                <emphasis remap='B'>wait</emphasis> commands either by the process id of the last process in the
                command pipeline (as stored in the <emphasis remap='B'>$!</emphasis> parameter) or by prefixing the
                job-number with a percent sign (<emphasis remap='B'>%</emphasis>).
                Other percent sequences can also be used to refer to jobs:
            </para>



            <informaltable pgwide='0' frame='none'>
                <tgroup cols='4' align='center'>
                    <colspec colname='c1'/>
                    <colspec colname='c2'/>
                    <colspec colname='c3'/>
                    <colspec colname='c4'/>
                    <thead>
                        <row>
                            <entry>%+</entry>
                            <entry align='right'>%+</entry>
                            <entry namest='c3' nameend='c4'>The most recently stopped job, or, if there are no stopped jobs, the oldest
                                running job.</entry>
                        </row>
                    </thead>
                    <tbody>
                        <row>
                            <entry>%%, <emphasis remap='P->B'>%</emphasis></entry>
                            <entry align='left'>%%, <emphasis remap='P->B'>%</emphasis></entry>
                            <entry align='left'>Same as <emphasis remap='B'>%+</emphasis>.</entry>
                        </row>
                        <row>
                            <entry>%-</entry>
                            <entry align='left'>%-</entry>
                            <entry align='left'>The job that would be the <emphasis remap='B'>%+</emphasis> job, if the later did not exist.</entry>
                        </row>
                        <row>
                            <entry>%<emphasis remap='I'>n</emphasis></entry>
                            <entry align='left'>%<emphasis remap='I'>n</emphasis></entry>
                            <entry align='left'>The job with job-number <emphasis remap='I'>n</emphasis>.</entry>
                        </row>
                        <row>
                            <entry>%?<emphasis remap='I'>string</emphasis></entry>
                            <entry align='left'>%?<emphasis remap='I'>string</emphasis></entry>
                            <entry align='left'>The job containing the string <emphasis remap='I'>string</emphasis> (an error occurs if multiple jobs
                                are matched).</entry>
                        </row>
                        <row>
                            <entry>%<emphasis remap='I'>string</emphasis></entry>
                            <entry align='left'>%<emphasis remap='I'>string</emphasis></entry>
                            <entry align='left'>The job starting with string <emphasis remap='I'>string</emphasis> (an error occurs if multiple jobs
                                are matched).</entry>
                        </row>
                    </tbody>
                </tgroup>
            </informaltable>

            <para>
                When a job changes state (<emphasis remap='I'>e.g.</emphasis>,
                a background job finishes or foreground
                job is stopped), the shell prints the following status information:
                <emphasis remap='B'>[</emphasis><emphasis remap='I'>number</emphasis><emphasis remap='B'>]</emphasis>
                <emphasis remap='I'>flag status command</emphasis>
                where
            </para>
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"&nbsp;<emphasis remap='I'>number</emphasis>"</term>
                    <listitem>
                        <para>
                            is the job-number of the job.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"&nbsp;<emphasis remap='I'>flag</emphasis>"</term>
                    <listitem>
                        <para>
                            is <emphasis remap='B'>+</emphasis> or <emphasis remap='B'>-</emphasis> if the job is the <emphasis remap='B'>%+</emphasis> or <emphasis remap='B'>%-</emphasis> job,
                            respectively, or space if it is neither.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"&nbsp;<emphasis remap='I'>status</emphasis>"</term>
                    <listitem>
                        <para>
                            indicates the current state of the job and can be
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->
            <!-- .RS -->
            <variablelist remap='.IP'>
                <varlistentry>
                    <term>"<emphasis remap='B'>Running</emphasis>"</term>
                    <listitem>
                        <para>
                            the job has neither stopped or exited (note that running does not
                            necessarily mean consuming CPU time &mdash; the process could be blocked waiting
                            for some event).
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>Done</emphasis> [<emphasis remap='B'>(</emphasis><emphasis remap='I'>number</emphasis><emphasis remap='B'>)</emphasis>]"</term>
                    <listitem>
                        <para>
                            the job exited. <emphasis remap='I'>number</emphasis> is the exit status of the job, which is
                            omitted if the status is zero.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='B'>Stopped</emphasis> [<emphasis remap='B'>(</emphasis><emphasis remap='I'>signal</emphasis><emphasis remap='B'>)</emphasis>]"</term>
                    <listitem>
                        <para>
                            the job was stopped by the indicated <emphasis remap='I'>signal</emphasis> (if no signal is given,
                            the job was stopped by SIGTSTP).
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"<emphasis remap='I'>signal-description</emphasis> [<emphasis remap='B'>(core dumped)</emphasis>]"</term>
                    <listitem>
                        <para>
                            the job was killed by a signal (<emphasis remap='I'>e.g.</emphasis>, Memory&nbsp;fault,
                            Hangup, <emphasis remap='I'>etc.</emphasis> &mdash; use
                            <userinput>kill -l</userinput> for a list of signal descriptions).
                            The <emphasis remap='B'>(core&nbsp;dumped)</emphasis> message indicates the process created a core file.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>"&nbsp;<emphasis remap='I'>command</emphasis>"</term>
                    <listitem>
                        <para>
                            is the command that created the process.
                            If there are multiple processes in the job, then each process will
                            have a line showing its <emphasis remap='I'>command</emphasis> and possibly its <emphasis remap='I'>status</emphasis>,
                            if it is different from the status of the previous process.
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist> <!-- .IP (gather_variableliist) -->

            <para>
                When an attempt is made to exit the shell while there are jobs in
                the stopped state, the shell warns the user that there are stopped jobs
                and does not exit.
                If another attempt is immediately made to exit the shell, the stopped
                jobs are sent a <emphasis remap='B'>HUP</emphasis> signal and the shell exits.
                Similarly, if the <option>nohup</option> option is not set and there are running
                jobs when an attempt is made to exit a login shell, the shell warns the
                user and does not exit.
                If another attempt is immediately made to exit the shell, the running
                jobs are sent a <emphasis remap='B'>HUP</emphasis> signal and the shell exits.
            </para>
        </refsect2>
    </refsect1>

    <refsect1 id='builtins'><title>BUILTIN UTILITIES</title>
            <para>
                    posh implements the following builtin utilities:
            </para>

            <itemizedlist mark='opencircle'>
                    <listitem>
                            <para>.
                            </para>
                    </listitem>
                    <listitem>
                            <para>:
                            </para>
                    </listitem>
                    <listitem>
                            <para>[
                            </para>
                    </listitem>
                    <listitem>
                            <para>break
                            </para>
                    </listitem>
                    <listitem>
                            <para>builtin
                            </para>
                    </listitem>
                    <listitem>
                            <para>continue
                            </para>
                    </listitem>
                    <listitem>
                            <para>eval
                            </para>
                    </listitem>
                    <listitem>
                            <para>exec
                            </para>
                    </listitem>
                    <listitem>
                            <para>exit
                            </para>
                    </listitem>
                    <listitem>
                            <para>false
                            </para>
                    </listitem>
                    <listitem>
                            <para>return
                            </para>
                    </listitem>
                    <listitem>
                            <para>set
                            </para>
                    </listitem>
                    <listitem>
                            <para>shift
                            </para>
                    </listitem>
                    <listitem>
                            <para>times
                            </para>
                    </listitem>
                    <listitem>
                            <para>trap
                            </para>
                    </listitem>
                    <listitem>
                            <para>wait
                            </para>
                    </listitem>
                    <listitem>
                            <para>read
                            </para>
                    </listitem>
                    <listitem>
                            <para>test
                            </para>
                    </listitem>
                    <listitem>
                            <para>true
                            </para>
                    </listitem>
                    <listitem>
                            <para>umask
                            </para>
                    </listitem>
                    <listitem>
                            <para>unset
                            </para>
                    </listitem>
                    <listitem>
                            <para>cd
                            </para>
                    </listitem>
                    <listitem>
                            <para>command
                            </para>
                    </listitem>
                    <listitem>
                            <para>echo
                            </para>
                    </listitem>
                    <listitem>
                            <para>export
                            </para>
                    </listitem>
                    <listitem>
                            <para>getopts
                            </para>
                    </listitem>
                    <listitem>
                            <para>kill
                            </para>
                    </listitem>
                    <listitem>
                            <para>local
                            </para>
                    </listitem>
                    <listitem>
                            <para>pwd
                            </para>
                    </listitem>
                    <listitem>
                            <para>readonly
                            </para>
                    </listitem>
            </itemizedlist>

    </refsect1>

    <refsect1 id='files'><title>FILES</title>
        <para>
          <filename>
            ~/.profile
    </filename>
          <filename>
            /etc/profile
    </filename>
          <filename>
            /etc/suid_profile
    </filename>
        </para>
    </refsect1>

    <refsect1 id='bugs'><title>BUGS</title>
        <para>
            Any bugs in posh should be reported via the Debian BTS.
            Legitimate bugs are inconsistencies between manpage and behavior,
            and inconsistencies between behavior and Debian policy
            (currently SUSv3 compliance with the following exceptions: echo
            -n, binary -a and -o to test, local scoping).
        </para>
    </refsect1>

    <refsect1 id='version'><title>VERSION</title>
        <para>
            This page documents the Policy-compliant Ordinary SHell.
        </para>
    </refsect1>

    <refsect1 id='authors'><title>AUTHORS</title>
        <para>
            This shell is based on pdksh.
        </para>
    </refsect1>

    <refsect1 id='see_also'><title>SEE ALSO</title>
        <para>
            <citerefentry><refentrytitle>awk</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>ksh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>dash</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>ed</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>getconf</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>getopt</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>sed</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>stty</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>vi</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>dup</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>getgid</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>getuid</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>open</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>pipe</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>wait</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>getopt</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>rand</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
            <citerefentry><refentrytitle>environ</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        </para>
    </refsect1>
</refentry>