First, you should always:

use strict;
use warnings;
use diagnostics;
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Next, you probably want to use the 3-argument version of open:

open(INFO, "<", "$infile") or die ("could not open file to append".$!)
+;
open(FILEA, "<", "outputfromvariantparser1.txt") or die ("could not op
+en file to write output");
open(FILEB,">>", output.txt") or die ("could not open file to write ou
+tput");
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You should probably lookup 'open' -- I see a problem with more than one of your files. (hint: one of the translations I did, above, does what your original code did but clearly doesn't do what you intend).

I don't think you want to nest your loops.

You'll need to figure out how to cycle through 'raw_data'

Edit: I made one hint a little clearer.

#!/usr/bin/perl
use warnings;
use strict;

my $infile = 'test.txt';

open INFO,  '<',  $infile or die "could not open '$infile' $!";
open FILEA, '<',  'outputfromvariantparser1.txt' or die "could not ope
+n 'outputfromvariantparser1.txt' $!";
open FILEB, '>>', 'output.txt' or die "could not open 'output.txt' $!"
+;

my @raw_data = <FILEA>;

while ( my $line = <INFO> ) {
    $line =~ s/TEXT TO BE REPLACED.*/$raw_data[0]/s;
    print FILEB $line;
    push @raw_data, shift @raw_data;
    }
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Nice solution. Liked particularly the way you make the array go on circles. There is one thing though. Given that input data the regexp is not considering the |. Maybe $line =~ s/\| TEXT TO BE REPLACED.*/ $raw_data[0]/s;

I have two files one is a Text file where I have some different Patterns and another one is ASCII file where I have code to generate a test pattern. I need Perl Script where I can transfer data pattern to that ASCII file, after particular word "PI".

File 1-

Result  is : 10000000     10000000     10000000     10000000     10000
+000     00000011 00000011 00000011 00000011 00000011
  10000001 10000001 10000001 10000001 10000001
  11000000 11000000 11000000 11000000 11000000
  01100000 01100000 01100000 01100000 01100000
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File 2-

CHAIN_TEST =

    pattern = 0;
    apply "grp1_load" 0 =
        chain "chain1" = "010";
    end;
    force   "PI" "XX0XXXXXX" 1;
    measure "PO" "XX" 2;
    apply "grp1_unload" 3 =
        chain "chain1" = "010";
    end;

    pattern = 1;
    apply "grp1_load" 0 =
        chain "chain1" = "101";
    end;
    force   "PI" "XX0XXXXXX" 1;
    measure "PO" "XX" 2;
    apply "grp1_unload" 3 =
        chain "chain1" = "101";
    end;

end;

SCAN_TEST =

    pattern = 0;
    apply "grp1_load" 0 =
        chain "chain1" = "010";
    end;
    force   "PI" "100000000" 1;
    measure "PO" "10" 2;
    pulse "/CK" 3;
    apply "grp1_unload" 4 =
        chain "chain1" = "010";
    end;
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2018-01-25 Athanasius added code and paragraph tags

Put a unique marker in the file eg <PATTERN> where you want the substitution.

#!/usr/bin/perl
use strict;
use warnings;

my $infile1 = 'file1.txt';
my $infile2 = 'file2.txt';
my $outfile = 'result.txt';

#open IN,'<',$infile1 or die "$infile1 : $!";
#my @file1 = <IN>;
#chomp(@file1);
#close IN;
my @file1 = qw(10000000 00000011 
               10000001 11000000 01100000  );

#open IN,'<',$infile2 or die "$infile2 : $!";
#my @file2 = <IN>;
#close IN;
my @file2 = <DATA>;

open OUT,'>',$outfile or die "$outfile : $!";
for my $pattern (@file1){
  print "Test pattern is $pattern\n";
  for (@file2){
    my $line = $_; # copy to preserve @file2
    $line =~ s/<PATTERN>/$pattern/;
    print OUT $line;
  }
}
close OUT;

__DATA__
SCAN_TEST =

    pattern = 0;
    apply "grp1_load" 0 =
        chain "chain1" = "010";
    end;
    force   "PI" "<PATTERN>" 1;
    measure "PO" "10" 2;
    pulse "/CK" 3;
    apply "grp1_unload" 4 =
        chain "chain1" = "010";
    end;
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poj

Better form is to add at the end of your original question Revised: new comments.