I recommend Regexp::Assemble for something like this. An example: 
use warnings;
use strict;
use Regexp::Assemble;

my @keywords = qw(
    a an the then that this
);

my $key_rea = Regexp::Assemble->new;
$key_rea->add($_) for @keywords;
my $key_re = $key_rea->re;

my $data = do { undef $/; <DATA> };
print "$1\n" while $data =~ m/(\b$key_re\b)/g;

__DATA__
hello everyone, i had been trying to make a lexical analyzer for c, wh
+ere all the keywords were to be inputted in a text file keywords. thi
+s i stored in an array. but this process is not being automated. the 
+code i wrote is as follows :-
...
the keywords file contains:- auto continue enum if short break switch 
+volatile default extern int signed typedef while case do float long s
+izeof union char double for register static unsigned const else goto 
+return struct void

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In reply to Re: how to automate the regular expression match from a file? by eff_i_g
in thread how to automate the regular expression match from a file? by vikashiiitdm

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