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Full Discussion: sed in a for loop
Top Forums UNIX for Dummies Questions & Answers sed in a for loop Post 302124423 by drl on Saturday 30th of June 2007 05:41:10 PM
Old 06-30-2007
Hi.

Here is a method to efficiently run sed on the data file only once. It uses sed to create a sed script file that can then be used in a single pass over the data file.

For small files, this will not make much difference, but with large data files, you will save all but one (or two) executions of sed, where n is the number of lines you are changing:
Code:
#!/bin/sh

# @(#) s1       Demonstrate creation of sed script for single-pass.

set -o nounset
echo " sh version: $BASH_VERSION" >&2

# Create the line number test file, can be in any order.

cat >numbers <<EOF
4
7
3
EOF

# Create the test data file.

cat >data1 <<EOF
one
two
three
four
five
six
seven
eight
nine
ten
EOF

# Create the sed script file with sed, for example:
# make
# 44
# into
# 44s/^/,/

sed 's|$|s/^/,/|' numbers >script

# Now efficiently run sed once instead of n times, display the
# data.

sed -f script data1

exit 0

which produces:
Code:
% ./s1
 sh version: 2.05b.0(1)-release
one
two
,three
,four
five
six
,seven
eight
nine
ten

cheers, drl
 

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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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