dear AnomalousMonk ;

thank you for your time. But it is not working in perl. I down know why? Shoudl i jusy replace my file name and i omitted the line for the $sol.because before that i read the variable from the text file and print it and it worked.any other point?

use strict;
use warnings;

die "usage: perl $0 file.name \n" unless @ARGV;;
my $filename_in  = "topol1.top";

print "processing '$filename_in' \n";

my $filename_out = "$filename_in.new";

open my $fh_in,  '<', $filename_in  or die "opening '$filename_in': $!
+";
open my $fh_out, '>', $filename_out or die "opening '$filename_out': $
+!";

while (<$fh_in>) {
  s{ (SOL) [^\n]* }{$1 $sol1}xmsg;
  print $fh_out $_ or die "writing '$filename_out': $!";
  }

close $fh_in  or die "closing '$filename_in': $!";
close $fh_out or die "closing '$filename_out': $!";

rename $filename_in, "$filename_in.bak" or die "renaming '$filename_in
+': $!";
rename $filename_out, $filename_in      or die "renaming '$filename_ou
+t': $!";
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2017-08-16 Athanasius added code tags