Testing if a string is a substring

[monkfan]

Guys,
I'm wondering if there is a better/faster way to do it. Here is my current working code.

#!/usr/bin/perl -w
use strict;

my $super = 'AAAAATT';
my $sub   =  'AT';     # Returns 1 (True)
#my $sub  =  'AAA';    # Returns 1 (True)
#my $sub  =  'GGG';    # Returns 0 (False)

print is_subst($super,$sub), "\n";

sub is_subst
{
    my  ($super,$sub)   = @_;
    my   $sup_len = length $super;
    my   $sub_len = length $sub;

    foreach  (my $i = 0; $i<$sup_len; $i++)
    {
       my $str = substr($super,$i,$sub_len);

       if ( $str eq $sub )
       {
           return 1;
           last;
       }
    }

    return 0;
}

[monarch]

#!/usr/bin/perl -w
use strict;

my $super = 'AAAAATT';
my $sub   =  'AT';     # Returns 1 (True)
#my $sub  =  'AAA';    # Returns 1 (True)
#my $sub  =  'GGG';    # Returns 0 (False)

print "1\n" if ( $super =~ m/\Q$sub\E/ );

[reasonablekeith]

I wouldn't use a regex for this, there aren't any patterns, just plain old string matching

my $super = 'AAAAATT';
my $sub   =  'AT';

print "1\n" if (index($super, $sub) != -1);

[davorg]

Ouch. Do you like making life hard for yourself :)

I think you're looking for the index function.

[gjb]

The index functions is also your friend, see the relevant perldoc.

However, for serious work (i.e. long strings) you may want to have a look at the following book:

@BOOK{Gusf97,
  title = {Algorithms on strings, trees and sequences},
  publisher = {Cambridge University Press},
  year = {1997},
  author = {Dan Gusfield},
  address = {Cambridge},
}

or the BioPerl project.

Hope this helps, -gjb-

[Zaxo]

That is what index is made for:

sub is_subst {
    my ($string, $subst) = @_;
    -1 != index( $string, $subst);
}

You may just want to call index directly, since it returns the location in $string of the first match.