Add a line after every string match - perl

Question

I have a sample file here http://pastebin.com/m5m40nGF
What I want to do is add a line after every instance of protein_id.
protein_id always has the same pattern:
TAB-TAB-TAB-protein_id-TAB-gnl|CorradiLab|M715_#SOME_NUMBER
What I need to do is to add this after every line of protein_id:
TAB-TAB-TAB-transcript_id-TAB-gnl|CorradiLab|M715_mRNA_#SOME_NUMBER
The catch is that #SOME_NUMBER has to stay the same.
In the first case, it would look like this:
94 1476 CDS
protein_id gnl|CorradiLab|M715_ECU01_0190
transcript_id gnl|CorradiLab|M715_mRNA_ECU01_0190
product serine hydroxymethyltransferase
label serine hydroxymethyltransferase
Thanks! Adrian
I tried a perl solution, but I get an error.
open(IN, $in); while(<IN>){
print $_;
if ($_ ~= /gnl\|CorradiLab\|/) {
$_ =~ s/tprotein_id/transcript_id/;
print $_;
}
}
Error:
syntax error at test.pl line 3, near "$_ ~"
syntax error at test.pl line 7, near "}"
Execution of test.pl aborted due to compilation errors.

Answer 1

The following perl script worked
my $in=shift;
open(IN, $in); while(<IN>){
print $_;
if ($_ =~ /gnl\|CorradiLab\|/) {
my $tmp = $_;
$tmp =~ s/protein_id/transcript_id/;
print $tmp;
}
}

Answer 2

Offering an update on existing answer because I feel it can be improved further:
Generally - the precise problem in the OP is this line:
if ($_ ~= /gnl\|CorradiLab\|/) {
Because you've got ~= not =~. That's what syntax error at test.pl line 3, near "$_ ~" is trying to tell you.
I would offer that improving on:
my $in=shift;
open(IN, $in); while(<IN>){
print $_;
if ($_ =~ /gnl\|CorradiLab\|/) {
my $tmp = $_;
$tmp =~ s/protein_id/transcript_id/;
print $tmp;
}
}
while ( my $tmp = <IN> ) { skips the need to assign $_.
3 argument open with lexical filehandle is preferable. E.g. open ( my $in, "<", "$input_filename" ) or die $!; (You should test whether the open worked too)
Explicit open may well be unnecessary if you're just reading a filename from command line. Using <> either reads filenames (opening and processing) or STDIN, which means your script becomes a bit more versatile.
Thus I would rewrite as:
#!/usr/bin/perl
use strict;
use warnings;
while ( my $line = <> ) {
print $line;
if ( $line =~ /gnl\|CorradiLab\|/ ) {
$line =~ s/protein_id/transcript_id/;
print $line;
}
}
Or alternatively:
#!/usr/bin/perl
use strict;
use warnings;
while (<>) {
print;
if (m/gnl\|CorradiLab\|/) {
s/protein_id/transcript_id/;
print;
}
}