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most efficient way to find a string in a file.

Posted on 1998-08-22
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Last Modified: 2010-03-04
What's the most efficient way to find a string in a file?
reading the file line by line and make a match?
while $ligne=<IN>
if $ligne =~ /pattern/
???
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Question by:steph84
6 Comments
 

Author Comment

by:steph84
ID: 1204449
Oh yes, and something I forgot, I want to make an EXACT match, I don't want that bob searched in bobby return true.
How to make an exact match??!!
Thanks.
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Expert Comment

by:ozo
ID: 1204450
$/="\nbob\n";
if( $ligne=<IN> ){
  print "EXACT match for 'bob' found";
}
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Accepted Solution

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mitek earned 200 total points
ID: 1204451

undef $/;
$data = <IN>;
unless ($data =~ /\bbob\b/){
  print "EXACT match for 'bob' found";
}
undef $data

P.S. $/="\nbob\n" would find bob only if this word is on a separate line all by itself. /\bbob\b/ will look for any word boundary.

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LVL 85

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by:ozo
ID: 1204452
steph84 said exact match, not word boundary match,
but word boundary match does seem more likely to be what was meant.
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by:b2pi
ID: 1204453
Oh, come on... at least a warning here....

Although it's definitely faster (well, maybe not definitely--marginally may sometimes be the appropriate word, depends on your buffer size, disk sector size, etc) to read in that entire file, that entire file may be of such a size that you start paging huge quantities everytime you try and move. (I'll grant that I'm only talking about files which are, say, 1/4 the size of your physical memory).  
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Expert Comment

by:mitek
ID: 1204454
that's right. if you even suspect that you may have a file of that size, the algorithm would be different and more complicated. then, it would be necessary to read in blocks of let's say, 4M in memory one by one, do lookup, load in another block, etc. probably, an overkill if one doesn't deal with files > 4M ...
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