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

hi monks, i had small retrival code in my project.. i need to match three consecutive copies of what ever is contained currently in $string .If $string=abc then it should match for abcabcabc i had implemented a code for this one. can any one suggest a better code to this?? 
#!/usr/bin/perl -w
my $string = "rid";
while (<>) {
if (/($string){3}/) {
print;
}
}

[download]

Replies are listed 'Best First'.
Re: can any reply out with a better code than this??
by ysth (Canon) on Dec 06, 2007 at 07:27 UTC
    Better in what sense?

    If the string may contain characters special to a regex that you want treated as regular characters to match, do /(\Q$string\E){3}/.

    Make the match non-capturing, since you are unlikely to be using the captured result: /(?:\Q$string\E){3}/.

    If the "3" is always the same and for some reason it isn't fast enough, try repeating it: /\Q$string$string$string\E/.

    Save the regex in a variable and reuse it: my $regex = qr/\Q$string$string$string\E/; ... if ($line =~ $regex) ....

    --
    CollegeGear.com - more than just college gear (though, yes, we have college-branded teddy bears)
[reply]
[d/l]
[select]
Re: can any reply out with a better code than this??
by fenLisesi (Priest) on Dec 06, 2007 at 07:44 UTC
    can any one suggest a better code to this?? 
    #!/usr/bin/perl -w
my $string = "rid";
while (<>) {
if (/($string){3}/) {
print;
}
}

    [download]
    Yes, for sure: 
    #!/usr/bin/perl -w

my $string = "rid";
while (<>) {
    if (/($string){3}/) {
        print;
    }
}

    [download]
    and, arguably: 
    use strict;

my $string = 'ri\d+';
while (my $line = <>) {
    if ($line =~ m{ (?: \Q$string\E ){3} }xms) {
        print $line;
    }
}

    [download]
[reply]
[d/l]
[select]
      the code above mentioned is not printing the matched content
[reply]
        Sorry, asdfghjkl, I confused you by changing the string. Try running it with ri\d+ri\d+ri\d+ for a match. That was meant to emphasize the use of \Q...\E.
[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom