fastest pattern match

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

I am a new bie.. I have a file having 50,000 lines. I want to match a pattern. I read the whole file in an array and then match the regex. I want only the line with the first match. the code is something like :-

open( FILE, "file" ) || die ("The file not there ");
#open the file with 50,000 lines (some 1MB memory)
@list=<FILE>; # put this in an array.
close(DICTIONARY); # close the file

$regex="somebla.."; #this is the regex to be matched
@match=grep(/$regex/,@list); 
#the above line returns an array of all lines matched 
# but I want only first one !! Pity don't know how to   
# get only that..

print $match[0];
#so I get the first match of the retrned array..
#that is poor .grep has to go through the complet list 
# although I need the first match only
[download]

I request the help from perl monks.. With lot of thanks!! Pandey

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Re: fastest pattern match by lestrrat (Deacon) on Jun 24, 2002 at 19:38 UTC
Untested `#!/usr/local/bin/perl use strict; open( FILE, "file" ) \|\| die $!; while( <FILE> ) { if( /regexp/ ) { print; last; } }` [download] or better yet ( also untested ) `perl -ne 'print, last if /regexp/' file` [download]	[reply] [d/l] [select]
Re: Re: fastest pattern match by neilwatson (Priest) on Jun 24, 2002 at 19:43 UTC
`last;` that's the command I was trying to remember. Not exit. My head is filled with to much useless information. Neil Watson watson-wilson.ca	[reply] [d/l]
Re: fastest pattern match by neilwatson (Priest) on Jun 24, 2002 at 19:35 UTC
Read the file one line at a time. When you hit your match exit: `open( FILE, "file" ) \|\| die ("The file not there "); while (<>){ if (m/$regex/) { print "matched!\n"; close (FILE); exit; } }` [download] Neil Watson watson-wilson.ca	[reply] [d/l]
Re^2: fastest pattern match by flounder99 (Friar) on Jun 24, 2002 at 19:50 UTC
You should use `m/$regex/o` or the regex will be compiled every iteration, slowing things down considerably -- flounder	[reply] [d/l]
Re: Re^2: fastest pattern match by japhy (Canon) on Jun 24, 2002 at 22:29 UTC
Incorrect. It will not be compiled on every iteration, but its string form will be compared with its previous string form, to see whether it needs recompiling. _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area) `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply]
Re^4: fastest pattern match by flounder99 (Friar) on Jun 25, 2002 at 11:53 UTC
Re: JANRQ :O( by frankus (Priest) on Jun 25, 2002 at 12:40 UTC
That's JAN-AR-IK..(like generic) Just another Regexp Question. Also it might be worth mentioning that meta characters in $regex will still be parsed. Make sure you intended that to happen. -- Brother Frankus. ¤	[reply]
Re: Re^2: fastest pattern match by d4vis (Chaplain) on Jun 24, 2002 at 20:11 UTC
Good advice in general, but in this case there'll only be one interation. Update: Fastolfe's right...my bad...mea culpa ~monk d4vis #!/usr/bin/fnord	[reply]
Re: Re: Re^2: fastest pattern match by Fastolfe (Vicar) on Jun 24, 2002 at 20:25 UTC
Re: fastest pattern match by Cody Pendant (Prior) on Jun 25, 2002 at 04:05 UTC
Just want to note that if this is your actual code: `open( FILE, "file" ) \|\| die ("The file not there "); [snip] close(DICTIONARY); # close the file` [download] you're opening one file, then closing another... -- `($_='jjjuuusssttt annootthheer pppeeerrrlll haaaccckkeer')=~y/a-z//s;print;` [download]	[reply] [d/l] [select]