if you want to check whats the fastest way to replace a string in Perl you could use the Benchmark-Module.I compared 4 different ways :
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#!/usr/bin/perl use strict; use warnings; use Benchmark qw(:all) ; use Inline 'C'; my $teststring; #check result : $teststring = "teststring1"; $teststring =~ s/1/2/g; print $teststring.$/; $teststring = "teststring1"; $teststring =~ s/1/2/go; print $teststring.$/; $teststring = "teststring1"; $teststring =~ tr/1/2/; print $teststring.$/; $teststring = "teststring1"; $teststring = replace($teststring,"1","2"); print $teststring.$/; $teststring = "teststring1"; $teststring = repl_str($teststring,"1","2"); print $teststring.$/; #test one cmpthese(-4, { 'regex_normal' => sub {$teststring = "teststring1"; $teststring =~ s/1/2/g; }, 'regex_optimised' => sub {$teststring = "teststring1"; $teststring =~ s/1/2/go; }, 'translate' => sub {$teststring = "teststring1"; $teststring =~ tr/1/2/; }, 'perl_sub' => sub {$teststring = "teststring1"; $teststring = replace($teststring,"1","2"); }, 'C_replace_string' => sub {$teststring = "teststring1"; $teststring = repl_str($teststring,"1","2"); }, }); #test two cmpthese(-4, { 'regex_normal' => sub {$teststring = "teststring1stringxstring"; $teststring =~ s/string/test/g; }, 'regex_optimised' => sub {$teststring = "teststring1stringxstring"; $teststring =~ s/string/test/go; }, 'translate' => sub {$teststring = "teststring1stringxstring"; $teststring =~ tr/string/test/; }, 'perl_sub' => sub {$teststring = "teststring1stringxstring"; $teststring = replace($teststring,"string","test"); }, 'C_replace_string' => sub {$teststring = "teststring1stringxstring"; $teststring = repl_str($teststring,"string","test"); }, }); sub replace { my $string = shift; my $old = shift; my $new = shift; my $pos = index($string, $old); while ( $pos > -1 ) { substr( $string, $pos, length( $old ), $new ); $pos = index( $string, $old, $pos + length( $new )); } return($string); } __END__ __C__ char* repl_str(const char *str, const char *old, const char *new){ char *ret, *r; const char *p, *q; size_t oldlen = strlen(old); size_t count, retlen, newlen = strlen(new); if (oldlen != newlen) { for (count = 0, p = str; (q = strstr(p, old)) != NULL; p = q + oldlen) count++; retlen = p - str + strlen(p) + count * (newlen - oldlen); } else retlen = strlen(str); if ((ret = malloc(retlen + 1)) == NULL) return NULL; for (r = ret, p = str; (q = strstr(p, old)) != NULL; p = q + oldlen) { ptrdiff_t l = q - p; memcpy(r, p, l); r += l; memcpy(r, new, newlen); r += newlen; } strcpy(r, p); return ret; } |
the result looks like:
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teststring2 teststring2 teststring2 teststring2 teststring2 Rate perl_sub C_replace_string regex_normal regex_optimised translate perl_sub 632214/s -- -68% -68% -70% -91% C_replace_string 1961177/s 210% -- -2% -8% -71% regex_normal 1999403/s 216% 2% -- -7% -71% regex_optimised 2142180/s 239% 9% 7% -- -69% translate 6843359/s 982% 249% 242% 219% -- Rate perl_sub regex_normal regex_optimised C_replace_string translate perl_sub 430150/s -- -50% -50% -57% -92% regex_normal 861549/s 100% -- -0% -14% -85% regex_optimised 862213/s 100% 0% -- -14% -85% C_replace_string 998062/s 132% 16% 16% -- -82% translate 5603343/s 1203% 550% 550% 461% -- |
Always check you sub results (Line 1-5) and make more test cases,
at the first case (Line 6) we see that for single character the best solution is to use regex.If you want to replace a longer string better use a C function.But in both cases its better to use the /o flag for regex to optimize, but then you cant interpolate a string in to the regex.And if you only want to replaxe use tr its the fastest.
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