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Top Forums Shell Programming and Scripting Performance Issue for a file search command Post 303001176 by Tanu on Friday 28th of July 2017 11:04:28 AM
Old 07-28-2017
Performance Issue for a file search command

Hi All,

This query is regarding performance improvement of a command.

I have a list of IDs in a file (say file1 with single ID column) and file2 has the data rows.

I need to get the IDs from file1 and search in file2, matching rows from file2 should be written to a file3.

For this scenario I have been using below command-

Code:
 for ID in `cat file1`; do grep $ID file2; done > file3

The command I am using is super slow. Can someone please let me know how can I improve the performance here.


Thanks in advance,
Tanu
 

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MERGE(1)						      General Commands Manual							  MERGE(1)

NAME
merge - three-way file merge SYNOPSIS
merge [ options ] file1 file2 file3 DESCRIPTION
merge incorporates all changes that lead from file2 to file3 into file1. The result ordinarily goes into file1. merge is useful for com- bining separate changes to an original. Suppose file2 is the original, and both file1 and file3 are modifications of file2. Then merge combines both changes. A conflict occurs if both file1 and file3 have changes in a common segment of lines. If a conflict is found, merge normally outputs a warning and brackets the conflict with <<<<<<< and >>>>>>> lines. A typical conflict will look like this: <<<<<<< file A lines in file A ======= lines in file B >>>>>>> file B If there are conflicts, the user should edit the result and delete one of the alternatives. OPTIONS
-A Output conflicts using the -A style of diff3(1), if supported by diff3. This merges all changes leading from file2 to file3 into file1, and generates the most verbose output. -E, -e These options specify conflict styles that generate less information than -A. See diff3(1) for details. The default is -E. With -e, merge does not warn about conflicts. -L label This option may be given up to three times, and specifies labels to be used in place of the corresponding file names in conflict reports. That is, merge -L x -L y -L z a b c generates output that looks like it came from files x, y and z instead of from files a, b and c. -p Send results to standard output instead of overwriting file1. -q Quiet; do not warn about conflicts. -V Print RCS's version number. DIAGNOSTICS
Exit status is 0 for no conflicts, 1 for some conflicts, 2 for trouble. IDENTIFICATION
Author: Walter F. Tichy. Manual Page Revision: 1999-08-27; Release Date: 23:37:10Z. Copyright (C) 1982, 1988, 1989 Walter F. Tichy. Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Paul Eggert. SEE ALSO
diff3(1), diff(1), rcsmerge(1), co(1). BUGS
It normally does not make sense to merge binary files as if they were text, but merge tries to do it anyway. GNU
23:37:10Z MERGE(1)
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