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Full Discussion: Performance issue with 'grep' command for huge file size
Operating Systems HP-UX Performance issue with 'grep' command for huge file size Post 302574529 by arb_1984 on Thursday 17th of November 2011 12:24:54 PM
Old 11-17-2011
Performance issue with 'grep' command for huge file size

I have 2 files; one file (say, details.txt) contains the details of employees and another file (say, emp.txt) has some selected employee names. I am extracting employee details from details.txt by using emp.txt and the corresponding code is:
Code:
while read line
do
emp_name=`echo $line`
grep -e $emp_name details.txt >> output.txt
done < emp.txt

Above code is working fine and I am getting expected result. But, this code is taking too much time (I don't have exact time, more than 6 hrs, later on cancelled the script) while the file size is huge. As an example, I have details.txt of around 2.5GB and record count is around 7.5lacs and the emp.txt has 55K employee name. Can you please suggest any other option/ command which will be better to handle such huge file. Thanks.
Last edited by vbe; 11-18-2011 at 09:33 AM.. Reason: attempt to use code tags ( fighting with fonts...)
 

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LEARN ABOUT REDHAT

mac2unix

dos2unix(1)						      General Commands Manual						       dos2unix(1)

NAME

       dos2unix - DOS/MAC to UNIX text file format converter

SYNOPSYS

       dos2unix [options] [-c convmode] [-o file ...] [-n infile outfile ...]

       Options:

       [-hkqV] [--help] [--keepdate] [--quiet] [--version]

DESCRIPTION

       This manual page documents dos2unix, the program that converts plain text files in DOS/MAC format to UNIX format.

OPTIONS

       The following options are available:

       -h --help
	      Print online help.

       -k --keepdate
	      Keep the date stamp of output file same as input file.

       -q --quiet
	      Quiet mode. Suppress all warning and messages.

       -V --version
	      Prints version information.

       -c --convmode convmode
	      Sets conversion mode. Simulates dos2unix under SunOS.

       -o --oldfile file ...
	      Old file mode. Convert the file and write output to it. The program default to run in this mode. Wildcard names may be used.

       -n --newfile infile outfile ...
	      New  file  mode.	Convert the infile and write output to outfile. File names must be given in pairs and wildcard names should NOT be
	      used or you WILL lost your files.

EXAMPLES

       Get input from stdin and write output to stdout.

	      dos2unix

       Convert and replace a.txt. Convert and replace b.txt.

	      dos2unix a.txt b.txt

	      dos2unix -o a.txt b.txt

       Convert and replace a.txt in ASCII conversion mode.  Convert and replace b.txt in ISO conversion mode.  Convert	c.txt  from  Mac  to  Unix
       ascii format.

	      dos2unix a.txt -c iso b.txt

	      dos2unix -c ascii a.txt -c iso b.txt

	      dos2unix -c mac a.txt b.txt

       Convert and replace a.txt while keeping original date stamp.

	      dos2unix -k a.txt

	      dos2unix -k -o a.txt

       Convert a.txt and write to e.txt.

	      dos2unix -n a.txt e.txt

       Convert a.txt and write to e.txt, keep date stamp of e.txt same as a.txt.

	      dos2unix -k -n a.txt e.txt

       Convert and replace a.txt. Convert b.txt and write to e.txt.

	      dos2unix a.txt -n b.txt e.txt

	      dos2unix -o a.txt -n b.txt e.txt

       Convert c.txt and write to e.txt. Convert and replace a.txt.  Convert and replace b.txt. Convert d.txt and write to f.txt.

	      dos2unix -n c.txt e.txt -o a.txt b.txt -n d.txt f.txt

DIAGNOSTICS

BUGS

       The program does not work properly under MSDOS in stdio processing mode.  If you know why is that so, please tell me.

AUTHORS

       Benjamin Lin - <blin@socs.uts.edu.au>

       Bernd Johannes Wuebben (mac2unix mode) <wuebben@kde.org>

MISCELLANY

       Tested environment:

	      Linux 1.2.0 with GNU C 2.5.8

	      SunOS 4.1.3 with GNU C 2.6.3

	      MS-DOS 6.20 with Borland C++ 4.02

       Suggestions and bug reports are welcome.

SEE ALSO

       unix2dos(1) mac2unix(1)

1995.03.31							   dos2unix v3.0						       dos2unix(1)
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