How do I pull n characters off the front of a string?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (strings)

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Re: How do I pull n characters off the front of a string?⭐ by arturo (Vicar) on Apr 24, 2001 at 20:59 UTC
Bah! Why use regexes when there's a faster function designed for the purpose? =) `#assuming $n contains the number ... my $first_n = substr($string, 0, $n); #to grab $n off the end my $last_n = substr($string, -1, $n);` [download]	[reply] [d/l]
Re: How do I pull n characters off the front of a string?⭐ by davido (Cardinal) on Oct 03, 2003 at 01:31 UTC
The other examples all handed off the first $n characters. But they didn't remove those first $n characters from the original $string, as the question required. As always, there is more than one way to do it. For each of the examples below, assume the following setup: `my $string = "1234567890abcdefghijABCDEFGHIJK"; my $chars; my $n = 2;` [download] With substr: `$chars = substr( $string, 0, $n ); substr( $string, 0, $n ) = "";` [download] Another with substr: `( $chars, $string ) = ( substr($string,0,$n), substr($string,$n) );` [download] And probaby the best substr solution: `$chars = substr ($string, 0, $n, "");` [download] With a substitution s/// regexp: `$string = s/^(.{$n})(.)$/$2/s; $chars = $1;` [download] With split: `($chars, $string) = split /^(.{$n})/, $string, 1;` [download] With a pattern match (m//): `($chars, $string) = $string =~ /^(.{$n})(.)$/s;` [download] With unpack (Not for the faint of heart): `( $chars, $string ) = unpack "a$n a@{[length($string)-$n]}", $string;` [download]	[reply] [d/l] [select]
Re: Answer: How do I pull n characters off the front of a string? by Aristotle (Chancellor) on Oct 03, 2003 at 22:31 UTC
unpack: `($chars, $string) = unpack "a$n a", $string;` [download] The four parameter substr is clearly the cleanest solution though. Makeshifts last the longest.*	[reply] [d/l]
Re: How do I pull n characters off the front of a string?⭐ by perlmonkey (Hermit) on May 02, 2001 at 11:48 UTC
Use substr when possible, it can be many times faster then a simple regex: `my $a = "abcdefghijklmnopqrstuvwxyz"; use Benchmark; timethese(1000000, { 's1' => sub { s1($a, 5) }, 's2' => sub { s2($a, 5) }, }); sub s1 { my $a = $_[0]; $a =~ s/^.{$_[1]}//; return $a; } sub s2 { substr($_[0], $_[1]); } Results: s1: 8 wallclock secs ( 7.95 usr + 0.09 sys = 8.04 CPU) s2: 2 wallclock secs ( 2.54 usr + 0.01 sys = 2.55 CPU)` [download]	[reply] [d/l]
Re: How do I pull n characters off the front of a string? by xtrem (Novice) on Apr 24, 2001 at 20:29 UTC
`my ($x,$y) = ($string =~ /^(.{n})(.{n})/);` [download] This will put the 1st n char into `$x` and the 2nd n chars into `$y` without touching `$string`... if you want the rest of the chars: `my ($x, $y, $rest) = ($string =~ /^(.{n})(.{n})(.*)/);` [download] if you don't like regexp's you can allways try substr	[reply] [d/l] [select]
Re: How do I pull n characters off the front of a string? by cbraga (Pilgrim) on May 01, 2001 at 22:47 UTC
Or this way: `#assuming $n contains the number $string =~ s/^(.{$n})//; $first_n = $1;` [download] Originally posted as a Categorized Answer.	[reply] [d/l]
Re: How do I pull n characters off the front of a string? by Masem (Monsignor) on Apr 24, 2001 at 20:26 UTC
`my ($x,$y) = ( $string =~ /^(.{$n})(.)$/ );` [download] Originally posted as a Categorized Answer.*	[reply] [d/l]