I have added the code that you have supplied.
what I want to do is match the specified strings from each graph_set.out file and print strings into .txt file.
It's not printing anything into the .txt file ? ?

#!/usr/local/bin/perl 

for (my $c = 1;; $c ++) {
    my $file = "graph_set_$c.out";
    last unless -f $file;
    open my $fh => "<", $file or die "Failed to open $file: $!";

local $/ = undef;       # undef record seperator
my $string = <IN>;         # read whole file into string    
close (IN);

my @gset_match = ($string =~ /([A-Z]\s\d+,\s\d+\(\s*\d+\))/g);

open (TEXT, ">graph_set.txt") or die "Can't create graph_set.txt: $!\n
+";
foreach $_(@gset_match) { print TEXT "$_\n"; }
close TEXT; 
}
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