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Top Forums Shell Programming and Scripting Shell Scripting Problem - Invalid Back Reference Post 302674349 by johnhisenburg on Thursday 19th of July 2012 12:09:08 PM

07-19-2012

Registered User

Shell Scripting Problem - Invalid Back Reference

Here is the question...

Create a new script, sub2, taking three parameters...

1.) the string to be replaced
2.) the string with which to replace it
3.) the name of the file in which to make the substitution

...that treats the string to be replaced as plain text instead of as a regular expression.

Hint 1: Try to get the string to be replaced into a shell variable (e.g., $target). Then use a sed command to rewrite any special regular expression characters in that string so that they get treated as text, storing the result in a second shell variable (e.g., $newTarget). Then issue the actual command to perform the substitutions on the file.

Hint 2: For technical reasons, this task is probably easier accomplished in /bin/sh than in /bin/csh. If you insist upon using csh to run your script, you might need to solve this by writing your sed commands into a separate temparary file and using the -f option of sed to run commands from that file.

This is what I've got so far, but for some reason I keep getting the same error message...

Code:

#!/bin/bash
# Script to substitute text

# 0.00 17Jul2012 AI Copy sub1.sh
# 0.01 17Jul2012 AI Convert target to plain text
# 0.02 18Jul2012 AI basename $3

# Usage:
# ./sub2.sh string replace file

echo $1                # Echo options
echo $2
echo $3

plain=`echo "$1" | sed 's/./\\\&/g'`    # Convert target to plain text

basetmp=`basename $3`
tmpfile="/tmp/$basetmp.$$"        # Unique temporary file
sed "s/$plain/$2/g" "$3" > "$tmpfile"    # Edit
mv "$tmpfile" "$3"        # Recover edits

and the error message I get is...

sed: -e expression #1, char 8: Invalid back reference

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lr_environment

LR_ENVIRONMENT.IN(1)					  LogReport's Lire Documentation				      LR_ENVIRONMENT.IN(1)

NAME

       lr_environment - Export Lire configuration in shell script form

SYNOPSIS

       eval `lr_environment`

DESCRIPTION

       The lr_environment command is used to import the Lire configuration in Lire shell scripts.

       All of Lire configuration variables will be written in a format that can be evaled by the shell.

       Shell scripts don't usually have to use that command, since it is done by the defaults file sourced by each command.

       The old names used by when the configuration was done in shell script are also exported by this script for backward compatibility.

AUTHOR

	 Francis J. Lacoste <flacoste@logreport.org>

VERSION

       $Id: lr_environment.in,v 1.12 2006/07/23 13:16:33 vanbaal Exp $

COPYRIGHT

       Copyright (C) 2003 Stichting LogReport Foundation LogReport@LogReport.org

       This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by
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       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program (see COPYING); if not, check with
       http://www.gnu.org/copyleft/gpl.html.

Lire 2.1.1							    2006-07-23						      LR_ENVIRONMENT.IN(1)