Not sure how stable is the file structure, maybe you really should write a parser, as suggests JavaFan, but the following example would work on the given input:

use strict;
use warnings;

open my $fh, "<", "file.frg";

while(<$fh>) {
    if (/^{FRG/../^}/){
        if (/^acc:(\d+)/) {
            print ">$1\n";
        }
        elsif ( /^seq:/ ) {
            while(<$fh>) {
                last if /^\./;
                print;
            }
        }
    }
}
[download]

Thank you very much zwon! Your script work just fine for me. I've made some changes to the code so that I can define what is the input file. But I'm not sure whether this is the correct way of doing it or not. Thank you for showing me how the regex work to match certain text i want. Thank you


my ($frg) = @ARGV;
$frgfile = "$frg";
open(frgfile) or die("Unable to open FRG file");

while(<frgfile>) {
    if (/^{FRG/../^}/){
        if (/^acc:(\d+)/) {
            print ">$1\n";
        }
        elsif ( /^seq:/ ) {
            while(<frgfile>) {
                last if /^\./;
                print;
            }
        }
    }
}
[download]

my ($frg) = @ARGV;
$frgfile = "$frg";
open(frgfile) or die("Unable to open FRG file");
[download]

That's very confusing form. It's a good practice to always start your scripts with

use strict;
use warnings;
[download]

this may help you to avoid many problems. In this case you would see some warnings. I'd write this as follows:

open my $fd, '<', $ARGV[0] or die $!;
while (<$fd>) {
...
[download]

Note how you can store filehandle in scalar variable.

Here is a slightly different approach to zwon's where I only read the file in one place and use state variables to keep track of where we are in the data file.

use strict;
use warnings;

my $frgFile = q{spw768164.frg};
open my $frgFH, q{<}, $frgFile or die qq{open: < $frgFile: $!\n};

my $inFRG = 0;
my $inSeq = 0;

while( <$frgFH> )
{
    if( $inFRG )
    {
        if( m|^\}| )
        {
            $inFRG = 0;
        }
        elsif( $inSeq )
        {
            if( m{^\.} )
            {
                $inSeq = 0;
            }
            else
            {
                print;
            }
        }
        elsif( m{^acc:(\d+)} )
        {
            print qq{>$1\n};
        }
        elsif( m{^seq:} )
        {
            $inSeq = 1;
        }
        else
        {
            ;
        }
    }
    else
    {
        next unless m|^\{FRG|;
        $inFRG = 1;
    }
}

close $frgFH or die qq{close: < $frgFile: $!\n};
[download]

The output.

>1101077781160
acaaggctggagtatttttttgtttagtaatttatttaattcagtttttatattttcataaactttttta
ggatcaccagggccattacttaaaaaaaaaccatcaaaatttctattaattatatcctcagcattaaaat
tgatctttagagagaaacttacctttgaaaatatattttttgttataaattaaatatccgttttgataat
taagtttagttttattatctaatacgggcatattaaatcatgtgtattagtatattatatcaaaggaaat
tcaaatgagtttggcaaaaaaatttctgatgacgttaaagtgctttaaaaggcggagatagaaaaacttt
catagcaaggtatgtctattctgagttaaaaattttctattaaagaaatctagagagagacgtgcttaat
tatctgacga
>1101077781161
gcgtgacgtttgagcagaagaattatttattaatttctgaggattttaagtctttaaaacaaaacgtttc
attcaaatttcaaaatcttgattataaagaagcgatggcactaatggctgagattggcaatattaatata
caactggctcagcagtattaaaaattgaactagatgcgttggaatctcaagggttaggaagaacagtttc
taatccaaattgtttaccctagacaatcaaactgccagtattaaac
[download]

I hope this is of interest.

Thanks JohnGG for demonstrating another method for pattern matching. Will look into this code in detail so that I can apply the knowledge to the future scripts! Thanks !!

From the example I'd say writing a parser is fairly trivial, but without a spec of how such an FRG file can be formatted it's hard to say. But that isn't any different from trying to solve the problem with a handful of regexes.

I agree with you that writing a parser to parse the entire file is more feasible and can be use to extract other information. For this script, i would like to learn how to confine searches from the input text. From here, I should learn and apply it to make it a better parser. I'm very interested to know how to parse a text file to a list of hash, as when the file getting very big, it would be ideal to speed up the search process?

#!/usr/bin/perl

use strict;

while (<DATA>) {
    if ( /^{FRG/ ... /^}/ ) {
        print ">$1\n" if /^acc:(\d+)/;
        if ( /^seq:/ ... /^\./ ) {
            next if ( /^seq:/ or /^\./ );
            print;
        }
    }
}
[download]

Thanks for the solution, it quick and easy just to pass out the data that i needed. It works as well! TQ!