Regular Expression

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

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Re: Regular Expression by dragonchild (Archbishop) on Feb 09, 2005 at 19:21 UTC
`if ($string =~ m/abc/i && $string =~ m/xyz/i) {` Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply] [d/l]
Re: Regular Expression by ikegami (Patriarch) on Feb 09, 2005 at 19:33 UTC
It can be done with a single regular expression (`$string =~ /^(?=.?abc).?xyz/i`), but you're better off using two (as dragonchild suggested) for readability.	[reply] [d/l]
Re: Regular Expression by Enlil (Parson) on Feb 09, 2005 at 19:34 UTC
You can do this a variety of ways, but here are three: `$string =~ m/abc.xyz\|xyz.abc/i $string =~ m/(?=.abc)(?=.xyz)/i; $string =~ /abc/i and $string =~ /xyz/i` [download] The ampersands inside the regular expression will be matched as ampersands and not used as logical operators. -enlil	[reply] [d/l]
Re^2: Regular Expression by nobull (Friar) on Feb 09, 2005 at 20:14 UTC
`$string =~ m/(?=.abc)(?=.xyz)/i;` [download] That unanchored pattern is pathologically inficient. If the string does not match it will try and fail at every character position. Even with a relatively short strings this has a considerable effect. `use Benchmark; my $string = 'x' x 100; timethese 1_000_000 => { unanchored => sub { $string =~ /(?=.abc)(?=.xyz)/i }, anchored => sub { $string =~ /^(?=.abc)(?=.xyz)/i }, };` [download] Benchmark: timing 1000000 iterations of anchored, unanchored... anchored: 1 wallclock secs ( 1.30 usr + 0.00 sys = 1.30 CPU) @ 768049.16/s (n=1000000) unanchored: 70 wallclock secs (70.12 usr + 0.00 sys = 70.12 CPU) @ 14261.06/s (n=1000000)	[reply] [d/l] [select]
Re: Regular Expression by TedPride (Priest) on Feb 09, 2005 at 19:30 UTC
Or you can lowercase a copy of $string and use index calls, which is my personal choice if a lot of finds are required.	[reply]
Re: Regular Expression by gopalr (Priest) on Feb 11, 2005 at 06:44 UTC
Hi `&` is a special character one. That's why it doesn't match. Use the following: `if (($string=~m/abc/i && $string=~m/xyz/i)) { print "\nMatched"; }` [download] Or Simply use `if ($string=~m#(abc).*?(xyz)#i) { print "\nfound"; }` [download]	[reply] [d/l] [select]
Re: Regular Expression by Roy Johnson (Monsignor) on Feb 09, 2005 at 21:33 UTC
Um...nobody suggested `(keys %{{map {$_=>1} /abc\|xyz/gi}} == 2)` [download] I wonder why. Caution: Do not take internally.	[reply] [d/l]
Re^2: Regular Expression by Eimi Metamorphoumai (Deacon) on Feb 09, 2005 at 22:05 UTC
Perhaps because it would accept the text "abcABC" and reject the text "abcABCxyz"? Now, `(keys %{{map {lc,1} /abc\|xyz/gi}} == 2)` would work...	[reply] [d/l]
Re^3: Regular Expression by Roy Johnson (Monsignor) on Feb 09, 2005 at 23:53 UTC
Touché. Caution: Contents may have been coded under pressure.	[reply]
Re^2: Regular Expression by Tanktalus (Canon) on Feb 09, 2005 at 22:05 UTC
The picture you have on your home node is quite apt for this type of response. Thanks :-)	[reply]
Re: Regular Expression by sh1tn (Priest) on Feb 09, 2005 at 21:00 UTC
In case we search not only in the beginning: `use Benchmark; use strict; my $string = 'x' x 100; my $regex = qr{(?:abc\|xyz)}; timethese 1_000_000 => { unanchored => sub { $string =~ /$regex/i }, anchored => sub { $string =~ /^(?=.abc)(?=.xyz)/i }, }; __END__ Benchmark: timing 1000000 iterations of anchored, unanchored... anchored: 1 wallclock secs ( 1.55 usr + -0.01 sys = 1.53 CPU) @ 65 +2741.51/s (n=1000000) unanchored: 19 wallclock secs (19.37 usr + 0.00 sys = 19.37 CPU) @ 51 +615.57/s (n=1000000)` [download]	[reply] [d/l]