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Full Discussion: sed error: invalid reference
Top Forums Shell Programming and Scripting sed error: invalid reference Post 302709221 by Don Cragun on Wednesday 3rd of October 2012 01:00:52 AM
Old 10-03-2012
Quote:
Originally Posted by dlundwall
Hello all,
I am using sed to parse a particular part of a string and am having problems. I am getting the following error:
sed: -e expression #1, char 28: invalid reference \1 on `s' command's RHS
Here is the code I am using:
Code:
echo "Alarm SET:"
echo ""
echo "Date:            " $DATE
echo "Time:            " $TIME
echo "ModelName:       " $MNAME
TST=$(echo "$EVENTMSG" | sed -ne 's/.*odelName=(\w+[^.]+)/\1/p')
echo "Non-FQDN Name:    " $TST
Severity:                  " $SEV

Here is the output:
Code:
Alarm SET:
Date:             10/01/2012
Time:             13:26:49
ModelName:        twa-casql01.c.com
sed: -e expression #1, char 28: invalid reference \1 on `s' command's RHS
Non-FQDN Name:
Severity:         MAJOR

As you can see, something is not working when I try to parse $EVENTMSG. My expected outcome is:
Code:
Alarm SET:
Date:             10/01/2012
Time:             13:26:49
ModelName:        twa-casql01.c.com
Non-FQDN Name: twa-casql01
Severity:         MAJOR

Ultimately, I am trying to verify that the $MNAME is the non-FQDN formated name as the ModelName contained in the $EVENTMSG.

The regex syntax of:
Code:
(\w+[^.]+)

takes the FQDN (or Fully Qualified Domain Name) and pulls the dot (.) suffix off of it.

Any ideas?

MANY THANKS IN ADVANCE!!
As usual in your postings, you leave out a lot of details that are needed to help solve your problem:
  1. What is in the shell variable EVENTMSG? For the purposes of this thread, I will assume that it contains the lines:
    Code:
     ModelName=        twa-casql01.c.com

    and
    Code:
     AlarmSeverity= Critical

    and several other lines before and/or after these lines.
    On these lines, I have no idea whether the whitespace between ...= and the following data is one or more <tab>s, one or more <space>s, or a combination of <space>s and <tab>s. The search expressions used below allow any combination of one or more <space> and/or <tab> characters.
  2. You don't say what system you're using. It is obvious why you're getting the error you're getting on your sed command (you have a request to use backreference #1 in your replacement string, but you didn't define a subexpression in your BRE), but it isn't obvious whether or not the \w would be treated as a match for whitespace (as in perl) or treated as an escaped w as specified by the standards for BREs in the sed utility. And, BREs in the standard don't treat + as special in a BRE. (It means match one or more of the previous expression in an ERE, but it just matches a <plus-sign> in a BRE.
  3. You search for odelName=, but you seem to have ModelName: in what you want output. I will assume for now that $EVENTMSG contains <equals-sign>s, but you want to translate them to <colon>s in your output.
The suggested text here should work on UNIX-, Linux-, and BSD-systems as long as you're using a POSIX compatible shell (such as bash or ksh). (I use ksh so it is what is specified here, but I'm not using any ksh specific features.)

This example is an amalgam of your original posting and the updated text in your original posting:
Code:
#!/bin/ksh
EVENTMSG='Wed 26 Sep, 2012
 ModelType= Event message testing
 ModelName=        twa-casql01.c.com
 AlarmSeverity= Critical
 ActionEvent= Evacuate Immediately
 Payload= large raw data string'

SEV=$(printf "%s\n" "$EVENTMSG" | sed -ne "s/.*AlarmSeverity=[  ]*\(.*\)/\1/p")
TST=$(printf "%s\n" "$EVENTMSG" | sed -ne 's/.*ModelName=[      ]*\([^.]\{1,\}\).*/\1/p')

printf " AlarmSeverity:\t%s\n Non-FQDN Name:\t%s\n" "$SEV" "$TST"

Note that the first bracet expression in both sed statements is the four character sequence: <left-square-bracket>, <space>, <tab>, and <right-square-bracket>.

This script produces the following output on OS X (and should be the same on any system with a sed conforming to the standards:
Code:
 AlarmSeverity:	Critical
 Non-FQDN Name:	twa-casql01

I hope this helps,
Don
This User Gave Thanks to Don Cragun For This Post:
dlundwall
 

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