user-tools/substenv

   1 #!/usr/bin/env perl
   2
   3 =pod
   4
   5 =head1 NAME
   6
   7 substenv - Substitute environment variables in parameters and run the resulting command
   8
   9 =head1 SYNOPSIS
  10
  11 substenv [I<OPTIONS>] [--] I<COMMAND> [I<ARGS>]
  12
  13 =head1 DESCRIPTION
  14
  15 Replace all occurrances of C<$NAME> in I<COMMAND> and I<ARGS> to the I<NAME> environment
  16 variable's value, whatever I<NAME> would be, then run I<COMMAND> I<ARGS>.
  17 Support C<${NAME}> curly bracket notation too.
  18
  19 =head1 OPTIONS
  20
  21 =over 4
  22
  23 =item -a, --all
  24
  25 Replace all occurrances of any C<$NAME> (and C<${NAME}>) substring
  26 (for details see S<LIMITATIONS>).
  27 This is the default behaviur, unless B<-e> is given.
  28
  29 =item -e, --environment I<NAME>
  30
  31 Replace the occurrances of I<NAME> environment variable.
  32 May be specified more than once.
  33 If B<-a> option is NOT given, ONLY these I<NAME>s are replaced.
  34
  35 =item -k, --keep-undefined
  36
  37 Do not replace variables which are not defined (ie. not in the environment),
  38 but keep them as-is.
  39 By default they are replaced with the empty string.
  40
  41 =item --dryrun, --dry-run
  42
  43 Do not run I<COMMAND>, just print what would be executed.
  44
  45 =back
  46
  47 =head1 EXAMPLE
  48
  49 This function call, in C, runs substenv(1),
  50 note, there is no dollar-interpolation in C.
  51
  52  execve("substenv", ["substenv", "ls", "$HOME/.config"])
  53
  54 Then substenv issues this system call:
  55
  56  execve("ls", ["ls", "/home/jdoe/.config"])
  57
  58 =head1 LIMITATIONS
  59
  60 In "substitute all" mode (without B<-e> flag) it replaces only names
  61 with uppercase letters, digits, and underscore (C<[A-Z0-9_]+>),
  62 as env vars usually contain only these chars.
  63 However it still replaces variables with lowercase letters in C<${NAME}> notation,
  64 and specific variable(s) given in B<-e> option(s).
  65
  66 Does not honour escaped dollar marks, ie. C<\$>.
  67
  68 =head1 NOTES
  69
  70 Does not support full shell-like variable interpolation.
  71 Use a real shell for it.
  72
  73 =head1 RATIONALE
  74
  75 Sometimes you don't want a shell to be in the picture when composing commands,
  76 yet need to weave some environment variable into it.
  77
  78 =head1 SEE ALSO
  79
  80 envsubst(1) from gettext-base package
  81
  82 =cut
  83
  84
  85 use Data::Dumper;
  86 use Getopt::Long qw/:config no_ignore_case no_bundling no_getopt_compat no_auto_abbrev require_order/;
  87 use Pod::Usage;
  88 no if ($] >= 5.018), 'warnings' => 'experimental::smartmatch';
  89
  90
  91 $OptAlwaysAll = 0;
  92 $OptKeepUndef = 0;
  93 $OptDryRun = 0;
  94 @subst_env_only = ();
  95
  96 GetOptions(
  97         'a|all!' => \$OptAlwaysAll,
  98         'e|env|environ|environment=s@' => \@subst_env_only,
  99         'k|keep-undefined!' => \$OptKeepUndef,
 100         'dry-run|dryrun!' => \$OptDryRun,
 101         'help' => sub { pod2usage(-exitval=>0, -verbose=>99); },
 102         '<>' => sub { unshift @ARGV, @_[0]; die '!FINISH'; },
 103 ) or pod2usage(-exitval=>2, -verbose=>99);
 104
 105
 106 $bare_env_name_regex = '[A-Z_][A-Z0-9_]*';
 107 $bracketed_env_name_regex = '[^}]+';
 108 if(@subst_env_only)
 109 {
 110         my $specific_env_names_regex = join '|', map { quotemeta } @subst_env_only;
 111         if($OptAlwaysAll)
 112         {
 113                 $bare_env_name_regex = $specific_env_names_regex . '|' . $bare_env_name_regex;
 114                 $bracketed_env_name_regex = $specific_env_names_regex . '|' . $bracketed_env_name_regex;
 115         }
 116         else
 117         {
 118                 $bare_env_name_regex = $bracketed_env_name_regex = $specific_env_names_regex;
 119         }
 120 }
 121
 122 @run_cmd = ();
 123
 124 sub subst_env
 125 {
 126         my $varname = shift;
 127         my $whole_substring = shift;
 128         if(not $OptKeepUndef or exists $ENV{$varname}) {
 129                 return $ENV{$varname};
 130         }
 131         else {
 132                 return $whole_substring;
 133         }
 134 }
 135
 136 for my $arg (@ARGV)
 137 {
 138         $arg =~ s/\$(\{(?<NAME>$bracketed_env_name_regex)\}|(?<NAME>$bare_env_name_regex))/subst_env($+{'NAME'}, $&)/eg;
 139         push @run_cmd, $arg;
 140 }
 141
 142
 143 if($OptDryRun)
 144 {
 145         warn Dumper \@run_cmd;
 146 }
 147 else
 148 {
 149         exec {$run_cmd[0]} @run_cmd;
 150         ($errno, $errstr) = (int $!, $!);
 151         warn "$0: ${run_cmd[0]}: $errstr\n";
 152         exit 125+$errno;
 153 }