Perl - Grep open file more then once. Post: 302539772

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Top Forums Shell Programming and Scripting Perl - Grep open file more then once. Post 302539772 by drl on Monday 18th of July 2011 04:17:20 PM

07-18-2011

Registered User

Hi.

Quote:

Originally Posted by matrixmadhan

No need to open a file for grepping, when grep it does that automatically for you

File::Grep - search.cpan.org

Indeed File::Grep will open files for you. Here is a driver that lists data files, the perl code, and the results of counting lines in the files twice, then searching for a pattern in those same files:

Code:

#!/usr/bin/env bash

# @(#) s1	Demonstrate File::Grep, test driver for.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C perl

p=./p1

pl " Input data files data[12]:"
for file in data[12]
do
  pe
  pe " File $file:"
  cat $file
done

pl " perl script:"
cat $p

pl " Results:"
$p hi data*

exit 0

producing:

Code:

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny) 
GNU bash 3.2.39
perl 5.10.0

-----
 Input data files data[12]:

 File data1:
hi
hi 2

 File data2:
hi 3
lo
hi 4
by

-----
 perl script:
#!/usr/bin/env perl

# @(#) p1	Demonstrate File::Grep, perl grep on a file.

use File::Grep qw( fgrep fmap fdo );
use warnings;
use strict;

$File::Grep::SILENT = 0;
my ($keyword) = shift || die " Must have at least a keyword.\n";
print " keyword is :$keyword:\n";
my (@f) = @ARGV;
print " files are :@f:\n";

# fdo
print "\n";
my ($count) = 0;
fdo { $count++ } @f;
print "Pass 1 (no open), total lines in :@f: -- $count\n";

print "\n";
$count = 0;
fdo { $count++ } @f;
print "Pass 2 (no open), total lines in :@f: -- $count\n";

# fmap (fgrep is complex).
my (@matches);
print "\n";
print " Matches for :$keyword: in :@f: (no open)\n";
fmap { push( @matches, $_ ) if /$keyword/; } @f;
print @matches;

exit;

-----
 Results:
 keyword is :hi:
 files are :data1 data2:

Pass 1 (no open), total lines in :data1 data2: -- 6

Pass 2 (no open), total lines in :data1 data2: -- 6

 Matches for :hi: in :data1 data2: (no open)
hi
hi 2
hi 3
hi 4

Best wishes ... cheers, drl

drl

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LEARN ABOUT SUNOS

fgrep

fgrep(1)							   User Commands							  fgrep(1)

NAME

       fgrep - search a file for a fixed-character string

SYNOPSIS

       /usr/bin/fgrep [-bchilnsvx] [-e pattern_list] [-f pattern-file] [pattern] [file...]

       /usr/xpg4/bin/fgrep [-bchilnsvx] [-e pattern_list] [-f pattern-file] [pattern] [file...]

DESCRIPTION

       The  fgrep (fast grep) utility searches files for a character string and prints all lines that contain that string. fgrep is different from
       grep(1) and from egrep(1) because it searches for a string, instead of searching for a pattern that matches an  expression.  fgrep  uses  a
       fast and compact algorithm.

       The characters $, *, [, ^, |, (, ), and  are interpreted literally by fgrep, that is, fgrep does not recognize full regular expressions as
       does egrep. These characters have special meaning to the shell. Therefore, to be safe, enclose the entire string within single quotes (').

       If no files are specified, fgrep assumes standard input. Normally, each line that is found is copied to the standard output. The file  name
       is printed before each line that is found if there is more than one input file.

OPTIONS

       The following options are supported:

       -b	       Precedes  each  line  by the block number on which the line was found. This can be useful in locating block numbers by con-
		       text. The first block is 0.

       -c	       Prints only a count of the lines that contain the pattern.

       -e pattern_list Searches for a string in pattern-list. This is useful when the string begins with a -.

       -f pattern-file Takes the list of patterns from pattern-file.

       -h	       Suppresses printing of files when searching multiple files.

       -i	       Ignores upper/lower case distinction during comparisons.

       -l	       Prints the names of files with matching lines once, separated by new-lines. Does not repeat the names  of  files  when  the
		       pattern is found more than once.

       -n	       Precedes each line by its line number in the file. The first line is 1.

       -s	       Works silently, that is, displays nothing except error messages. This is useful for checking the error status.

       -v	       Prints all lines except those that contain the pattern.

       -x	       Prints only lines that are matched entirely.

OPERANDS

       The following operands are supported:

       file	       Specifies a path name of a file to be searched for the patterns. If no file operands are specified, the standard input will
		       be used.

   /usr/bin/fgrep
       pattern	       Specifies a pattern to be used during the search for input.

   /usr/xpg4/bin/fgrep
       pattern	       Specifies one or more patterns to be used during the search for input. This operand is treated as if it were  specified	as
		       -e pattern_list.

USAGE

       See largefile(5) for the description of the behavior of fgrep when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes).

ENVIRONMENT VARIABLES

       See  environ(5)	for  descriptions of the following environment variables that affect the execution of fgrep: LC_COLLATE, LC_CTYPE, LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0	If any matches are found

       1	If no matches are found

       2	For syntax errors or inaccessible files, even if matches were found.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

   /usr/bin/fgrep
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

   /usr/xpg4/bin/fgrep
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWxcu4			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ed(1), egrep(1), grep(1), sed(1), sh(1), attributes(5), environ(5), largefile(5), XPG4(5)

NOTES

       Ideally, there should be only one grep command, but there is not a single algorithm that spans a wide enough range of space-time tradeoffs.

       Lines are limited only by the size of the available virtual memory.

   /usr/xpg4/bin/fgrep
       The /usr/xpg4/bin/fgrep utility is identical to /usr/xpg4/bin/grep -F (see grep(1)). Portable applications  should  use	/usr/xpg4/bin/grep
       -F.

SunOS 5.10							    4 Oct 2002								  fgrep(1)

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