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[linux_from_scratch_hints.git] / OLD / shells.txt

TITLE:          How to install alternative shells on your LFS-system
LFS VERSION:    All
AUTHOR:         Björn Lindberg <d95-bli@nada.kth.se>

SYNOPSIS:       A guide on how to install other shells than bash on an 
                LFS-system.

HINT:

1. INTRODUCTION

A vanilla LFS only comes with one shell, namely bash (Bourne-again
shell). There are a lot of reasons why one would like to have
alternatives. Different shells are good at different things. You might
want to use one particular shell as your interactive shell, but another
one for scripting. There are some programs that have their compile
scripts written with a syntax that requires a certain shells. I will
give a brief description of each shell, listing some of their strong
points below.


1.1 The Almquist Shell (ash)

This is the shell that most closely tries to mimick the behaviour of
the original Bourne shell -- and no more. It is therefore Bourne shell
compliant, while being extraordinarily small and efficient. It is used
as the /bin/sh shell on NetBSD, who also currently maintains it. There
are two good reasons why you might want to consider installing ash:

(1) It is small. It's memory footprint is about a third of bigger more
    feature-filled shells, like bash and Korn shell. On a less
    powerful machine it could be installed as /bin/sh, causing all
    common administration scripts, eg. boot scripts to be run with it.

(2) Portability. On Linux systems it is commonplace to begin a script
    with /bin/sh, yet oftentimes bash-specific features will creep in,
    since bash is the Linux standard shell. Those scripts should
    arguably have /bin/bash at the top, because most of them won't run
    as intended on other flavors of UNIX that don't use bash for their
    /bin/sh, like the *BSDs and commercial Unices. Thus, using ash for
    /bin/sh is an extra insurance that your scripts are portable in
    the sense that they will generally work with the interpreter given
    on the first line. this is good.


1.2 The Korn Shell (ksh)

Korn shell, like bash, is an improved Bourne shell derivative. It is
actually more than a shell, designed to be a very high-level
programming language while still maintaining Bourne shell
compatibility. Bash has borrowed a lot of the ksh functionality, so
the syntax is very similar. Korn shell is commonly used for more
advanced scripting on non-Linux platforms, and since ksh is frequently
available on commerical Unices, the portability for ksh scripts is
good. It is also a very good interactive shell, and has some distinct
features, like co-processes. See http://www.kornshell.com for more info.


1.3 The T C Shell (tcsh)

T C shell is the successor of the C shell, a competitor to the Bourne
shell but with C-like syntax. tcsh thus has a vastly different syntax
than the Bourne shell derivatives. Although shell afficionados
consider csh (and by extension tcsh) a bad scripting shell (see
http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/), it is a very
nice interactive shell with some unique features, like programmable
tab completion. Another good reason to have it is that you might
encounter scripts written in csh or tcsh. Such scripts won't run with
Bourne shell and compatibles, since the syntax is different. Some
program sources requires tcsh to build, eq xv (the image viewer), and
openoffice. See http://www.tcsh.org for more info on tcsh.


1.4 The Z shell (zsh)

The Z shell is the most feature-filled (or bloated :-) of our
shells. It's syntax is mostly similar to the Korn shell, but also
borrowing elements from the C shell. It strongpoints are as an
interactive shell, where it incorporates features from all other
shells, while containing modules with a large variation of
functionality. As an example, zsh comes with it's built-in ftp-client!
See http://www.zsh.org for more info.


2. INSTALLATION


2.1 The Almquist Shell

As mentioned earlier, the most actively maintained ash is the one
NetBSD are using for their /bin/sh. Most Linux-distros are including
ash, and they are then typically keeping their sources in sync with
the NetBSD ones. We will use the Debian sources, since they are a bit
more Linux-friendly than NetBSD. :-)

It is still a lot of trouble to compile though, because the makefile
requires pmake, which is a make common on *BSDs. Gnu make won't
work. The tarballs we'll need, and the places I got them:

ash
        ftp://ftp.debian.org/debian/dists/potato/main/source/shells/\
                ash_0.3.5.orig.tar.gz
ash-diff
        ftp://ftp.debian.org/debian/dists/potato/main/source/shells/\
                ash_0.3.5-11.diff.gz
ash-hetios
        ftp://ftp.psychosis.com/linux/linux-router-devel/\
                ash-hetios-0.5.1.diff.gz
pmake
        ftp://ftp.debian.org/debian/dists/potato/main/source/devel/ \
                pmake_1.45-3.2.tar.gz

We might as well use the Debian pmake, found at the same place. Don't
hesitate to use your local Debian mirror site instead of the main one.

The ash-hetios patch is a patch from the Linux Router Project that
enables history support and arrow keys. If you plan on using ash as an
interactive shell, you would want this patch, and if not, just don't
apply it.

In the section below I will assume that you do not want to keep pmake
after using it to build ash. If you want to install pmake on your
system the procedure will actually be somewhat easier.

Unpack the pmake tarball and issue the following command:

        debian/rules

We will need this later:

        export PMAKE=<path-to-pmake>
        export PATH=$PATH:$PMAKE

If you want to install pmake on your system, instead do the following:

        install -m 755 bmake /usr/bin/pmake
        install -m 755 mkdep /usr/bin/
        install -m 644 make.1 /usr/share/man/man1/pmake.1
        install -m 644 mkdep.1 /usr/share/man/man1/
        install -d -m 755 /usr/share/mk/
        for file in mk/*; do install -m 644 $file /usr/share/; done

Now unpack the ash tarball and apply first the debian diff, and then
the hetios diff. The hetios diff will not apply cleanly beacuse it was
made against a slightly different source tree. This is nothing to
worry about.

We still have to make some small modifications:

        mv Makefile Makefile.orig
        sed 's/\(^CPPFLAGS.*$\)/\1 -DHETIO/' Makefile.orig > Makefile
        echo -e "#endif\n" >> hetio.c
        mv arith.y arith.y.orig
        sed 's/\(yyerrok;\)/\/* \1 *\//' arith.y.orig > arith.y
        $PMAKE/pmake -m $PMAKE/mk CFLAGS='-O2' CPPFLAGS='-DBSD \
                -DSMALL -DSHELL -DHETIO -D__COPYRIGHT\(x\)= \
                -D__RCSID\(x\)=' HOST_CPPFLAGS='-DBSD -DSMALL \
                -DSHELL -DHETIO -D__COPYRIGHT\(x\)= \
                -D__RCSID\(x\)=' YACC='bison -y'

Voilà! We now have a binary called sh and a manpage to go with
it. Install via the following:

        install -m 755 sh /bin/ash
        install -m 644 sh.1 /usr/share/man/man1/
        cd /usr/share/man/man1 && ln sh.1 ash.1

If you would like to use ash as /bin/sh, either symlink it or install
it as sh directly. The manpage is a very good manpage for sh in either
case.


2.2 The Korn Shell

The Korn SHell used to be a commercial closed-source shell. Because of
this, a free clone was written, pdksh (Public Domain Korn
Shell). pdksh supposedly has most of the original ksh's functionality,
but since early 2000 the source code for the original ksh is
available, so that is what we are going to install here. Note that ksh
is still under a license though. The following packages are needed:

http://www.research.att.com/~gsf/download/tgz/INIT.2002-06-28.tgz
http://www.research.att.com/~gsf/download/tgz/ast-ksh.2002-06-28.tgz
http://www.research.att.com/~gsf/download/tgz/ast-ksh-locale.2002-06-28.tgz

Note that the exact URL may change as a result of updates to the
source code packages. If the above links don't work you will have to
go to http://www.research.att.com/sw/download/ and manually download
the following packages: INIT, ast-ksh and ast-ksh-locale.

ksh is built using AT&T's particular build system. First you will need
to designate an empty build directory, eg <...>/src/ksh. The rest of
the install commands should be executed while standing in this
directory. Unpack the INIT package from this directory. Execute

        mkdir lib/package/tgz

and move all three packages to this directory. Now issue

        bin/package read
        bin/package make

To install ksh

        cp arch/linux.i386/bin/ksh /bin
        cp arch/linux.i386/man/man1/sh.1 /usr/share/man/man1/ksh.1

To install the provided shell functions pushd, popd and dirs, do this

        mkdir -p /usr/share/ksh/functions
        cp arch/linux.i386/fun/* /usr/share/ksh/functions

you will then have to set the following environment variable to access
them, this can be done in one of the startup scripts

        export FPATH=/usr/share/ksh/functions

The install management system supposedly will make it easier to
upgrade ksh to a newer version by the following command

        bin/package update source http://www.research.att.com/sw/download


2.3 The T C Shell

tcsh is by comparison easy to install. First we need the sources:

ftp://ftp.funet.fi/pub/unix/shells/tcsh/tcsh-6.11.tar.gz

Build the sources

        ./configure --prefix=/usr --bindir=/bin --mandir=/usr/share/man
        mv config_f.h config_f.h.orig
        sed '/NLS_CATALOGS/s/undef/define/; /AUTOLOGOUT/s/define/undef/' \
                config_f.h.orig > config_f.h
        make
        make install install.man

That's it! You now have a shiny new tcsh in your /bin directory. If
you have special considerations you might want to edit the settings in
config_f.h differently from mine, for instance it is possible to set
vi editing as default. If you want to play with the programmable tab
completion feature, have a look at the file complete.tcsh.


2.4 The Z Shell

The sources are available for instance here:

ftp://sunsite.dk/pub/unix/shells/zsh/zsh-4.0.4.tar.bz2

Building and installation is straightforward

        ./configure --prefix=/usr --bindir=/bin --mandir=/usr/share/man
        make
        make install

This will install, in addition to the shell, the shell modules as well
as a lot of shell functions. To take advantage of the latter, you need
to set the following environment variable, and also "autoload" the
functions you would like to use

        fpath=(/usr/share/zsh/4.0.4/functions/)
        autoload zed    # example


3. Startup files

To learn more about the different shells, I recommend the manpages and
homepages for the shells, as well as the general web resources listed
in section 5. I will however say something about startup files, which
is otherwise often a source of confusion.

Beginning with ash and ksh, all shells (interactive, non-interactive
and login) will read the file specified in $ENV. A login shell will in
addition to this first read /etc/profile and .profile. It is common to
set $ENV from one of those two files with a command such as this

        ENV=$HOME/.shrc; export ENV     # or
        export ENV=$HOME/.kshrc

To restrict parts of the $ENV file to interactive shells (that will
not be run for eg shell scripts), something like the following can be
used

        case $- in *i*)
                # interactive commands
                # ...
        esac

A tsch login shell will read the following files

        /etc/csh.cshrc
        /etc/csh.login
        ~/.tcshrc, or if not found, ~/.chsrc
        ~/.login

a non-login shell will only read /etc/csh.cshrc and ~/.tcshrc (or
~/.cshrc). On logout, a login shell will read /etc/csh.logout and
~/.logout.

A zsh login shell reads the following files

        /etc/zshenv
        ~/.zshenv
        /etc/zprofile
        ~/.zprofile
        /etc/zshrc
        ~/.zshrc
        /etc/zlogin
        ~/.zlogin

an interactive (but non-login) shell will read all those but the
*profile and *login files. A non-interactive shell will not read
*zshrc. In addition, zsh login shells will also read ~/.zlogout and
/etc/zlogout on exit.


4. Size comparisons

Shell   In-memory size (kB)     Binary size (kB)
-------------------------------------------
ash     472                     97
bash    1400                    533
ksh     1212                    834
tcsh    1448                    292
zsh     1472                    424

All binaries were stripped. The in-memory size is obtained from the
RSS column from 'top'. Sizes may vary slightly from system to system
and also depending on exact shell version. I am actually not certain
how relevant these figures are, but decided to include them for
comparison. Another thing to keep in mind is that zsh uses a lot of
modules that also takes up space, so the total disk space needed are
higher than the above figure. The total zsh installation uses over 3
MB.


5. Shell resources

http://www.shelldorado.com
http://www.faqs.org/faqs/unix-faq/shell/shell-differences/
http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/
http://www.kornshell.com
http://www.tcsh.org
http://www.zsh.org