extracting first n characters of a string in perl

ananthbv · 09-14-2004, 06:11 AM

hi everybody,
i am trying to write a perl script that extracts the first n characters (say 5) from 2 strings (both string s have more than n characters) and check whether they are same. i know how to take a string and check if it matches the first 5 characters of another string, but how how do i check for the first 5 chars of both strings?

Cedrik · 09-14-2004, 06:34 AM

I would do :

Code:

$str1 = "test12";
$str2  = "test1234";

$five_first = $str1;
$five_first =~ s/(^.{5}).*$/$1/;

if( $str2 =~ /^$five_first/) {
    print "5 first chars match\n";
}

ananthbv · 09-14-2004, 06:51 AM

that works perfectly! but help me understand this

Code:

$five_first =~ s/(^.{5}).*$/$1/;

the first five characters in 'five_first' are stored in $1 and the whole string $five_first is substituted with $1, right?

chrism01 · 09-14-2004, 06:57 AM

A simpler / more readable soln would be to use substr(0):
$value = substr($string, $offset, $count);
eg
$value = substr($string, 0, 5);
you could even compare the 2 strings in one hit:

Code:

if( substr($string1, 0, 5) eq substr($string2, 0, 5) )
{
    do something...
}

ananthbv · 09-14-2004, 07:25 AM

this is great, thanks a lot chris and cedrik.