Construct and execute multiple 2-argument commands using patterns to specify input/output pairs

multi.pl

#! /bin/perl

# multi.pl

# Parse command-line switches
use Getopt::Std;
%opt = ();
getopts('htqorlgO:', \%opt);

$usage  = "Usage: multi.pl [-hqorlt] cmd before_pat after_pat [files]\n";
$usage .= "  -h   _h_elp\n";
$usage .= "  -t   _t_est (print, but don't execute cmds)\n";
$usage .= "  -q   _q_uiet operation (no STDERR)\n";
$usage .= "  -o   cmd -o after_file before_file\n";
$usage .= "  -O x cmd -x after_file before_file\n";
$usage .= "  -r   cmd before_file > after_file\n";
$usage .= "  -l   _l_ist commands which yield STDOUT\n";
$usage .= "  -g   _g_lobal subsitution of before_pat->after_pat\n";
if ($opt{h}) {
  print $usage;
  exit;
}

$cmd   = shift @ARGV;
$befor = shift @ARGV;
$after = shift @ARGV;

unless (defined($cmd) and defined($befor) and defined($after)) {
    print "Usage: multi cmd before_pat after_pat\n";
    exit(1);
}

@oldfiles = (@ARGV > 0 ?
             @ARGV :
             glob("*$befor*"));

foreach $old (@oldfiles) {
  chomp $old;
  $new = $old;
  if ($opt{g}) { # global substitution
    $new =~ s/$befor/$after/g;
  } else {
    $new =~ s/$befor/$after/;
  }
  if ($opt{o}) { # -o switch
    $command = "$cmd -o $new $old";
  } elsif ($opt{O}) {
    ($lcmd = $cmd) =~ s/^(\S+)/$1 -$opt{O} $new/;
    $command = "$lcmd $old";
  } elsif ($opt{r}) { # output redirection
    $command = "$cmd $old > $new";
  } else {
    $command = "$cmd $old $new";
  }

  if ($opt{l}) { # list commands that yield STDOUT
    $stdout = `$command`;
    print "$command\n" if $stdout;
  } else {
    print "$command\n"                  unless $opt{q};
    system($command)                    unless $opt{t};
  }
}