vikashiiitdm has asked for the wisdom of the Perl Monks concerning the following question:

hello everyone, i had been trying to make a lexical analyzer for c, where all the keywords were to be inputted in a text file keywords. this i stored in an array. but this process is not being automated. the code i wrote is as follows :- 
#!/usr/bin/env perl
@keywd=`cat /home/vikash/maya/keywords`;
@operatr=`cat /home/vikash/maya/operators`;

print "<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+>";
foreach $keyword (@keywd){print "$keyword";}
print "<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+>";

print "\nthe total no. of keywords specified in the file are :($#keywd
+)\n";
print "hello $ENV{'USER'}, greetings !!!  you are ";
print "using display $ENV{'DISPLAY'} \n";

$file='/home/vikash/maya/new.c';
print "\n\n:Lexical Analysis Report:\n\n";
print " |->    Input Code File:- $file\n";
print <<"EOF";
\nThe code used in the lexical analysis is :- \n
EOF
print `cat /home/vikash/maya/new.c`;

for($i=0;$i<$#keywd;$i++)
{
print if /\b^int$\b/;

}

__END__

[download]
the keywords file contains:- auto continue enum if short break switch volatile default extern int signed typedef while case do float long sizeof union char double for register static unsigned const else goto return struct void the problem i'm having is that the keywords are not being taken automatically one after the another from this list of keywords............. if i do 
open(INFO,$file);
while(<INFO>){
print if /\bint\b/;
print if /\bfloat\b/;
}
close(INFO)

[download]
everything's fine........ but i don't want to enter all these keywords one by one. what if in future i were to add a new keyword. i would simply like to modify the keywords file not the whole code........

Replies are listed 'Best First'.
Re: how to automate the regular expression match from a file?
by eff_i_g (Curate) on Apr 06, 2011 at 19:37 UTC
    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

    [download]
[reply]
[d/l]
Re: how to automate the regular expression match from a file?
by toolic (Bishop) on Apr 06, 2011 at 19:07 UTC
[reply]
[d/l]
Re: how to automate the regular expression match from a file?
by wind (Priest) on Apr 06, 2011 at 19:29 UTC 
    
use Data::Dumper;

use strict;

my @keywords = qw(auto continue enum if short break switch volatile de
+fault extern int signed typedef while case do float long sizeof union
+ char double for register static unsigned const else goto return stru
+ct void);
my $keywords_re = join '|', @keywords;

my $file = '/home/vikash/maya/new.c';

open my $fh, $file or die $!;

my %keywords;
while (<$fh>) {
    while (m{\b($keywords_re)\b}g) {
        $keywords{$1}++;
    }
}

print Dumper(\%keywords);

    [download]
[reply]
[d/l]

      thanx for the code....but plz tell me why is this code not producing what i want. not a single keyword is displayed......

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