Testing if a string is a substring

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

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;
}
[download]

Regards,
Edward

Comment on Testing if a string is a substring Download Code

Replies are listed 'Best First'.
Re: Testing if a string is a substring by davorg (Chancellor) on Jul 20, 2005 at 08:57 UTC
Ouch. Do you like making life hard for yourself :) I think you're looking for the index function. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re: Testing if a string is a substring by Zaxo (Archbishop) on Jul 20, 2005 at 09:01 UTC
That is what index is made for: `sub is_subst { my ($string, $subst) = @_; -1 != index( $string, $subst); }` [download] You may just want to call index directly, since it returns the location in $string of the first match. After Compline, Zaxo	[reply] [d/l]
Re: Testing if a string is a substring by gjb (Vicar) on Jul 20, 2005 at 09:01 UTC
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-	[reply] [d/l]
Re: Testing if a string is a substring by monarch (Priest) on Jul 20, 2005 at 08:50 UTC
`#!/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/ );` [download]	[reply] [d/l]
Re^2: Testing if a string is a substring by reasonablekeith (Deacon) on Jul 20, 2005 at 08:58 UTC
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);` [download] --- my name's not Keith, and I'm not reasonable.	[reply] [d/l]