Perl escaping argument for bash execution

Question

I\'ve written some code in Perl which executes some bash command within its execution. My problem was when bash command attributes contained white space inside which failed

Answer 1

When calling directly from perl, as Glenn Jackman says, I would use system or exec to avoid quoting trouble and to capture the output, for example to compute the md5sum of a file:

my $pid, $safe_kid; 
die "cannot fork: $!" unless defined ($pid = open($safe_kid, "-|"));
if ($pid == 0) {
   # This is the child process, exec md5sum
   exec('/usr/bin/md5sum', '--binary', $filename) or die "can't exec md5sum: $!";
} else {
   # This is the parent process, read data (we do not need to wait for
   # child process termination)
   @sum = <$safe_kid>;
   close $safe_kid; # $? contains status 
}
if ($?!=0) {
   die "Problem computing hashsums on '$filename': $!\n";
}

On a related note, I was looking for a way to print command line arguments to the shell for the user to copy and paste. I hit upon the idea of single-quoting everything, and using echo to recompose the string if a single-quote was already present, although using String::ShellQuote seems to be a better idea, really:

#!/usr/bin/perl

use strict;

testEscapeForBash("Hello World");
testEscapeForBash("Hello World!");
testEscapeForBash("Nothing_special_here.txt");
testEscapeForBash("With'One Single Quote");
testEscapeForBash("With 'Two Single' Quotes");
testEscapeForBash("'With Surrounding Single Quotes'");
testEscapeForBash("With \$ Dollar Sign");
testEscapeForBash("With * Fileglob");
testEscapeForBash("With ! History Expansion Sign");
testEscapeForBash("   ");
testEscapeForBash(" Some surrounding spaces ");

sub testEscapeForBash {
   my ($in) = @_;
   my $out = escapeForBash($in);
   print "[$in] gives\n       $out\n";
}

sub escapeForBash {
   my ($name) = @_;
   if (!$name) {
      die "Empty name passed to 'escapeForBash'"
   }
   my @parts = split(/'/,$name,-1); # limit is negative to catch trailing quote
   my $res;
   if (@parts == 1) {
      $res = "'$name'"
   }
   elsif (@parts > 1) {
      $res = '$(echo ';
      my $first = 1;
      for my $part (@parts) {
         $res .= "\"'\"" unless $first;
         $first = 0;
         $res .= "'";
         $res .= $part;
         $res .= "'";
      }
      $res .= ')';
   }
   else {
      die "Weird number of parts: @parts"
   }
   return $res
}

Let's run this:

[Hello World] gives
       'Hello World'
[Hello World!] gives
       'Hello World!'
[Nothing_special_here.txt] gives
       'Nothing_special_here.txt'
[With'One Single Quote] gives
       $(echo 'With'"'"'One Single Quote')
[With 'Two Single' Quotes] gives
       $(echo 'With '"'"'Two Single'"'"' Quotes')
['With Surrounding Single Quotes'] gives
       $(echo ''"'"'With Surrounding Single Quotes'"'"'')
[With $ Dollar Sign] gives
       'With $ Dollar Sign'
[With * Fileglob] gives
       'With * Fileglob'
[With ! History Expansion Sign] gives
       'With ! History Expansion Sign'
[   ] gives
       '   '
[ Some surrounding spaces ] gives
       ' Some surrounding spaces '