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Full Discussion: SED: Replacing $1 with $2 escape problem
Top Forums Shell Programming and Scripting SED: Replacing $1 with $2 escape problem Post 302262445 by mark007 on Thursday 27th of November 2008 11:21:51 AM
Old 11-27-2008
SED: Replacing $1 with $2 escape problem
Hi all,

I have a script which uses sed to replace one string with another. The problem is, the string to be matched, and its replacement are coming in as two command line arguments $1 and $2

$1 and $2 can be absolutely anything, but both should be treated purely as strings. My sed command below doesn't do any escaping which is what I need.

sed "s/$1/$2/g" /tmp/input.txt > /tmp/output.txt

I spent a couple of days making some code which could escape these variables before use in my sed command and it seemed to allow me to enter almost anything but today, when trying to replace one string, with another string that contains an ampersand, some fancy sed backtracking came into play.

function escape {
new=`echo "$1" | sed 's/\\\\/\\\\\\\\/g' | sed 's/\//\\\\\//g' | sed 's/\*/\\\\\*/g' | sed 's/"/\"/g' | sed 's/\"/\\\\\"/g'`
echo $new
}

What I think I really need is a premade escape function for use in sed, or maybe some arguments to sed itself to ignore all special chars and treat them as strings.
 

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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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