Re: Bash scripting - pattern matching

8 Apr 2001

      On Sun, 8 Apr 2001, Andrew Smith wrote:

as> Hi
as> 
as> I'm writing a small bash script whereby I want part of it to check to see if
as> an argument given to then script is contained in a file. If not, it needs to
as> be added. For example:
as> 
as> /tmp/names is a file containing:
as> 
as> Tom
as> Dick
as> Harry
as> 
as> If my script (eg, /tmp/foo) is called as shown below:
as> 
as> /tmp/foo Gary
as> 
as> The script should add Gary to the file.
as> 
as> 
as> If my script is called as shown below:
as> 
as> /tmp/foo Harry
as> 
as> The script should return a message saying  Harry is already in the list.
as> 
as> 
as> 
as> This is what I have so far ($2 is the argument)
as> 
as> if ! [[cat /tmp/names | grep $2 = "$2"]]; then {
as>     echo>>"/tmp/names" "$2"
as>     echo "Name isn't already in the file. Name added!"
as> } else {
as>     echo "name is already in the file. Name is NOT added again."
as> } fi
as> 

  Your trying to use an argument that doesn't exist, the names your using
in the above examples reside at the 1st location, not the 2nd as your
using within your routine.
  Try the following

	#!/bin/sh
	#

	if [ ! `cat ./names | grep $1` ]; then
	    echo $1 >> ./names
	    echo "Name added!"
	else
	    echo "Name already exists in file."
	fi

skull@daydream:~/bin > cat ./names
Bill   
Charlie
Percy 
Fred
George
Ron  

skull@daydream:~/bin > ./foo Ron
Name already exists in file.

skull@daydream:~/bin > ./foo Ginny
Name added!

skull@daydream:~/bin > cat ./names
Bill
Charlie
Percy
Fred
George
Ron
Ginny

  Also, you'll want to add a check before the bulk of the script to see
that a name exists at argument location 1, otherwise it will fail and add
a blank line to the file. To get around this you could use the following
	test -z $1 && exit 1

which will just quietly exit the routine and do nothing, or the following
	if [ -z $1 ]; then
	    echo "Nothing supplied, exiting"
	    exit 1
	fi

which will at least tell you what happened.

as> It basically prints the file piped through grep and makes a judgement based
as> on the output. My problem is the script always thinks that a given name
as> isn't in the list and adds it, whether the name is in the file or not.
as> 
as> Could anyone help?
as> 
as> Many thanks,
as> 
as> 
as> 
as> Andrew Smith
as> 
as> 
as> 

-- 
        S.Toms - tomas@primenet.com - www.primenet.com/~tomas
                   SuSE Linux v7.0+ - Kernel 2.2.18

Sauron is alive in Argentina!