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Top Forums Shell Programming and Scripting Perl, searching multiple files and printing returned line to new file Post 302448005 by Yogesh Sawant on Wednesday 25th of August 2010 04:03:10 AM
Old 08-25-2010
are you still invoking grep command from your perl script? if yes, use the m operator of Perl instead.
here's a plan that could work for you:
1. get a list of all *.txt files, using opendir and readdir
2. open multiple threads
3. in each thread, open a single file from the list and search the string using m operator, append the results in the output file

but this approach would work only if i/o sub-system is fast in your system. otherwise cpu and memory would wait for io if disks are slower.
 

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PCREGREP(1)						      General Commands Manual						       PCREGREP(1)

NAME
pcregrep - a grep with Perl-compatible regular expressions. SYNOPSIS
pcregrep [-Vcfhilnrsvx] pattern [file] ... DESCRIPTION
pcregrep searches files for character patterns, in the same way as other grep commands do, but it uses the PCRE regular expression library to support patterns that are compatible with the regular expressions of Perl 5. See pcre(3) for a full description of syntax and semantics. If no files are specified, pcregrep reads the standard input. By default, each line that matches the pattern is copied to the standard out- put, and if there is more than one file, the file name is printed before each line of output. However, there are options that can change how pcregrep behaves. Lines are limited to BUFSIZ characters. BUFSIZ is defined in <stdio.h>. The newline character is removed from the end of each line before it is matched against the pattern. OPTIONS
-V Write the version number of the PCRE library being used to the standard error stream. -c Do not print individual lines; instead just print a count of the number of lines that would otherwise have been printed. If sev- eral files are given, a count is printed for each of them. -ffilename Read patterns from the file, one per line, and match all patterns against each line. There is a maximum of 100 patterns. Trailing white space is removed, and blank lines are ignored. An empty file contains no patterns and therefore matches nothing. -h Suppress printing of filenames when searching multiple files. -i Ignore upper/lower case distinctions during comparisons. -l Instead of printing lines from the files, just print the names of the files containing lines that would have been printed. Each file name is printed once, on a separate line. -n Precede each line by its line number in the file. -r If any file is a directory, recursively scan the files it contains. Without -r a directory is scanned as a normal file. -s Work silently, that is, display nothing except error messages. The exit status indicates whether any matches were found. -v Invert the sense of the match, so that lines which do not match the pattern are now the ones that are found. -x Force the pattern to be anchored (it must start matching at the beginning of the line) and in addition, require it to match the entire line. This is equivalent to having ^ and $ characters at the start and end of each alternative branch in the regular expression. SEE ALSO
pcre(3), Perl 5 documentation DIAGNOSTICS
Exit status is 0 if any matches were found, 1 if no matches were found, and 2 for syntax errors or inacessible files (even if matches were found). AUTHOR
Philip Hazel <ph10@cam.ac.uk> Last updated: 15 August 2001 Copyright (c) 1997-2001 University of Cambridge. PCREGREP(1)
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