How can I translate a shell script to Perl?

Question

I have a shell script, pretty big one. Now my boss says I must rewrite it in Perl. Is there any way to write a Perl script and use the existing shell code as is in my Perl scrip

Answer 1

I agree that learning Perl and trying to write Perl instead of shell is for the greater good. I did the transfer once with the help of the "Replace" function of Notepad++.

However, I had a similar problem to the one initially asked while I was trying to create a Perl wrapper around a shell script (that could execute it).

I came with the following code that works in my case.

It might help.

#!perl
use strict;
use Data::Dumper;
use Cwd;

#Variables read from shell
our %VAR;

open SH, "<$ARGV[0]" or die "Error while trying to read $ARGV[0] ($!)\n";
my @SH=;
close SH;

sh2perl(@SH);


#Subroutine to execute shell from Perl (read from array)
sub sh2perl {
    #Variables
    my %case; #To store data from conditional block of "case"
    my %if; #To store data from conditional block of "if"

    foreach my $line (@_) {
        #Remove blanks at the beginning and EOL character
        $line=~s/^\s*//;
        chomp $line;

        #Comments and blank lines
        if ($line=~/^(#.*|\s*)$/) {
            #Do nothing
        }

        #Conditional block - Case
        elsif ($line=~/case.*in/..$line=~/esac/) {
            if ($line=~/case\s*(.*?)\s*\in/) {
                $case{'var'}=transform($1);
            } elsif ($line=~/esac/) {
                delete $case{'curr_pattern'};
                #Run conditional block
                my $case;
                map { $case=$_ if $case{'var'}=~/$_/ } @{$case{'list_patterns'}};
                $case ? sh2perl(@{$case{'patterns'}->{$case}}) : sh2perl(@{$case{'patterns'}->{"*"}});
            } elsif ($line=~/^\s*(.*?)\s*\)/) {
                $case{'curr_pattern'}=$1;
                push(@{$case{'list_patterns'}}, $case{'curr_pattern'}) unless ($line=~m%\*\)%)
            } else {
                push(@{$case{'patterns'}->{ $case{'curr_pattern'} }}, $line);
            }
        }

        #Conditional block - if
        elsif ($line=~/^if/..$line=~/^fi/) {
            if ($line=~/if\s*\[\s*(.*\S)\s*\];/) {
                $if{'condition'}=transform($1);
                $if{'curr_cond'}="TRUE";
            } elsif ($line=~/fi/) {
                delete $if{'curr_cond'};
                #Run conditional block
                $if{'condition'} ? sh2perl(@{$if{'TRUE'}}) : sh2perl(@{$if{'FALSE'}});
            } elsif ($line=~/^else/) {
                $if{'curr_cond'}="FALSE";
            } else {
                push(@{$if{ $if{'curr_cond'} }}, $line);
            }
        }

        #echo
        elsif($line=~/^echo\s+"?(.*?[^"])"?\s*$/) {
            my $str=$1;
            #echo with redirection
            if ($str=~m%[>\|]%) { 
                eval { system(transform($line)) };
                if ($@) { warn "Error while evaluating $line: $@\n"; }
            #print new line
            } elsif ($line=~/^echo ""$/) {
                print "\n";
            #default
            } else {
                print transform($str),"\n";
            }
        }

        #cd
        elsif($line=~/^\s*cd\s+(.*)/) {
            chdir $1;
        }

        #export
        elsif($line=~/^export\s+((\w+).*)/) {
            my ($var,$exported)=($2,$1);
            if ($exported=~/^(\w+)\s*=\s*(.*)/) {
                while($exported=~/(\w+)\s*=\s*"?(.*?\S)"?\s*(;(?:\s*export\s+)?|$)/g) { $VAR{$1}=transform($2); }
            }
            # export($var,$VAR{$var});
            $ENV{$var}=$VAR{$var};
            print "Exported variable $var = $VAR{$var}\n";
        }


        #Variable assignment
        elsif ($line=~/^(\w+)\s*=\s*(.*)$/) {
            $1 eq "" or $VAR{$1}=""; #Empty variable
            while($line=~/(\w+)\s*=\s*"?(.*?\S)"?\s*(;|$)/g) {
                $VAR{$1}=transform($2);
            }
        }

        #Source
        elsif ($line=~/^source\s*(.*\.sh)/) {
            open SOURCE, "<$1" or die "Error while trying to open $1 ($!)\n";
            my @SOURCE=;
            close SOURCE;
            sh2perl(@SOURCE);
        }


        #Default (assuming running command)
        else {
            eval { map { system(transform($_)) } split(";",$line); };
            if ($@) { warn "Error while doing system on \"$line\": $@\n"; }
        }

    }
}


sub transform {
    my $src=$_[0];

    #Variables $1 and similar
    $src=~s/\$(\d+)/$ARGV[$1-1]/ge;

    #Commands stored in variables "$()"
    eval {
        while ($src=~m%\$\((.*)\)%g) {
            my ($cmd,$new_cmd)=($1,$1);
            my $curr_dir=getcwd;
            $new_cmd=~s/pwd/echo $curr_dir/g;
            $src=~s%\$\($cmd\)%`$new_cmd`%e;
            chomp $src;
        }
    };
    if ($@) { warn "Wrong assessment for variable $_[0]:\n=> $@\n"; return "ERROR"; }

    #Other variables
    $src=~s/\$(\w+)/$VAR{$1}/g;

    #Backsticks
    $src=~s/`(.*)`/`$1`/e;

    #Conditions
    $src=~s/"(.*?)"\s*==\s*"(.*?)"/"$1" eq "$2" ? 1 : 0/e;
    $src=~s/"(.*?)"\s*!=\s*"(.*?)"/"$1" ne "$2" ? 1 : 0/e;
    $src=~s/(\S+)\s*==\s*(\S+)/$1 == $2 ? 1 : 0/e;
    $src=~s/(\S+)\s*!=\s*(\S+)/$1 != $2 ? 1 : 0/e;

    #Return Result
    return $src;
}