ls -al "file 1" "file'2" ; cat /etc/passwd

##</code><code>##

ls '-al' 'file 1' 'file'\''2' ';' 'cat' '/etc/passwd'

##</code><code>##

#!/usr/bin/perl
# used http://www.cs.hmc.edu/courses/2003/spring/cs60/fsm.pdf
# to transform state machine into regexp
$cmd=<>;
$arg="";
chomp $cmd;
$cmd.=" ";
# regexp
# ( |([^'"\\ ]+)|(\\.)|("(([^"\\])|(\\.))*")|('[^']*'))
# only global matching
# ( |(?:[^'"\\ ]+)|(?:\\.)|(?:"(?:(?:[^"\\])|(?:\\.))*")|(?:'[^']*'))
# we need to do second subst to remove " and ' pairs and unescape \ so need some flags
# ( |(?:[^'"\\ ]+)|(\\.)|("(?:(?:[^"\\])|(\\.))*")|('[^']*'))
while($cmd=~s/^( |(?:[^'"\\ ]+)|(\\.)|("(?:(?:[^"\\])|(\\.))*")|('[^']*'))(.*)$/$6/)
{
  $c=$1;
  # the flags...
  $esc=$2;
  $dquote=$3;
  $dquoteEsc=$4;
  $squote=$5;
  print "c=$c arg=$arg cmd=$cmd esc=$esc dquote=$dquote dquoteEsc=$dquoteEsc squote=$squote\n";
  if($c eq " ")
  {
    $arg=~s/'/'\\''/g; # shell escape the '
    $res .= "'$arg' ";
    $arg="";
    next;
  }
  if(($esc ne "")|($dquoteEsc ne "")) { $c=~s/\\//g }
  if($dquote ne "") { $c =~ s/^"(.*)"$/$1/}
  if($squote ne "") { $c =~ s/^'(.*)'$/$1/}
  $arg .= $c;
}
print "$res\n";