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Full Discussion: Using sed to change values after a specific string
Top Forums Shell Programming and Scripting Using sed to change values after a specific string Post 302958342 by prodigious8 on Wednesday 21st of October 2015 11:18:05 AM
Old 10-21-2015
Using sed to change values after a specific string
Hello I have a script that searches a file for a specific string and then changes the nth column after that string. I have searched online for how to do this with sed but have not seemed to find a solution that works for me. I am using bash.

Some background info:
- Currently I am using awk to do this successfully.
- I was informed that sed with --in place set would be faster

the awk command I use is as follows

Code:
site='SITES'
mx=50
awk -v n="$site" -v a="$mx" '$1==n{$2=a}{print $0}' FS=' ' OFS=' ' $FILENAME &> tmp && mv tmp $FILENAME

What this does is finds the line where 'SITES' is written in the file (a label for that row) then changes the second element (column) of that row to mx (which is 50).

1. I want to know if its true that using sed will be faster (considering this is looped for thousands of files)
2. Also want to know how to implement with sed if thats the case. So far I have tried (and failed) the following:
Code:
sed -i {$site}'/s/\S\+/'"${mx}"'/2' $FILENAME

I think there might be a misconception that sed is faster and from what I researched awk is the better option. The person who told me sed is faster has much more experience than me but I have a feeling he is incorrect.
Last edited by prodigious8; 10-21-2015 at 03:38 PM..
 

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LEARN ABOUT DEBIAN

shtool-subst

SHTOOL-SUBST.TMP(1)					      GNU Portable Shell Tool					       SHTOOL-SUBST.TMP(1)

NAME

       shtool-subst - GNU shtool sed(1) substitution operations

SYNOPSIS

       shtool subst [-v|--verbose] [-t|--trace] [-n|--nop] [-w|--warning] [-q|--quiet] [-s|--stealth] [-i|--interactive] [-b|--backup ext]
       [-e|--exec cmd] [-f|--file cmd-file] [file] [file ...]

DESCRIPTION

       This command applies one or more sed(1) substitution operations to stdin or any number of files.

OPTIONS

       The following command line options are available.

       -v, --verbose
	   Display some processing information.

       -t, --trace
	   Enable the output of the essential shell commands which are executed.

       -n, --nop
	   No operation mode. Actual execution of the essential shell commands which would be executed is suppressed.

       -w, --warning
	   Show warning on substitution operation resulting in no content change on every file. The default is to show a warning on substitution
	   operations resulted in no content change on all files.

       -q, --quiet
	   Suppress warning on substitution operation resulting in no content change.

       -s, --stealth
	   Stealth operation. Preserve timestamp on file.

       -i, --interactive
	   Enter interactive mode where the user has to approve each operation.

       -b, --backup ext
	   Preserve backup of original file using file name extension ext.  Default is to overwrite the original file.

       -e, --exec cmd
	   Specify sed(1) command directly.

       -f, --file cmd-file
	   Read sed(1) command from file.

EXAMPLE

	#   shell script
	shtool subst -i -e 's;(c) ([0-9]*)-2000;(c) 1-2001;' *.[ch]

	#    RPM spec-file
	%install
	    shtool subst -v -n 
		-e 's;^(prefix=).*;1 $RPM_BUILD_ROOT%{_prefix};g' 
		-e 's;^(sysconfdir=).*;1 $RPM_BUILD_ROOT%{_prefix}/etc;g' 
		`find . -name Makefile -print`
	    make install

HISTORY

       The GNU shtool subst command was originally written by Ralf S.  Engelschall <rse@engelschall.com> in 2001 for GNU shtool.  It was prompted
       by the need to have a uniform and convenient patching frontend to sed(1) operations in the OpenPKG package specifications.

SEE ALSO

       shtool(1), sed(1).

18-Jul-2008							   shtool 2.0.8 					       SHTOOL-SUBST.TMP(1)
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