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Full Discussion: Speeding up shell script with grep
Top Forums Shell Programming and Scripting Speeding up shell script with grep Post 302994604 by bakunin on Saturday 25th of March 2017 05:27:04 AM
Old 03-25-2017
Quote:
Originally Posted by dunryc
master is a file which has been collated over a few years ad currently contains around 4 million numbers

new is a file which also contains 4 million number i need to split new nto two separate files one which contains number that already exist in master and one which contains numbers that don't already exist in master. I can do this but it takes around 80 hours to complete !! can any one offer any suggestions on how to speed this up ?
Use grep -f: instead of writing a shell loop grep can do it in one step (and presumably quite faster):

Code:
grep -f new_phone master > in_new_phone_and_master

You might want to try this with some small files to get a feeling for what it produces. You can also use all the other grep-options in conjunction withh this, especially "-F" (use fixed strings for matching), which speeds greps operation up considerably. Also notice the -v-option which inverts the outcome. See the man-page of grep for details.

I hope this helps.

bakunin
This User Gave Thanks to bakunin For This Post:
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LEARN ABOUT MINIX

zgrep

ZGREP(1)                                                      General Commands Manual                                                     ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  invokes  grep  on  compressed  or  gzipped  files.   These  grep  options  will  cause  zgrep  to  terminate  with  an  error  code:
       (-[drRzZ]|--di*|--exc*|--inc*|--rec*|--nu*).  All other options specified are passed directly to grep.  If no file is specified,  then  the
       standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed if necessary and fed to grep.

       If the GREP environment variable is set, zgrep uses it as the grep program to be invoked.

EXIT CODE

       2 - An option that is not supported was specified.

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), gzexe(1), gzip(1), zdiff(1), zforce(1), zmore(1), znew(1)

                                                                                                                                          ZGREP(1)
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