Changing contents of a file through shell script

*

#! /bin/sh
file=xyz.cfg
addr=$1
port=$2
username=$3
sed -i 's/address=.*/address='$addr'/' $file
sed -i 's/port=.*/port='$port'/' $file
sed -i 's/username=.*/username='$username'/' $file

*

I hope this one will be simpler to understand for beginners

sed -i 's/something/other/g' filename.txt 

Will edit filename.txt in-place, and change the word 'something' to 'other'

I think -i may be a GNU extension though, but if it's OK for you, you can add it via find, xargs etc.

If you would like to change it in a shell script, you can take arguments on the command-line and refer to them by number, eg $1

Edit:

As per my comment, sudo_O's answer below is exactly the example that you want. What I will add is that it's common that you'll want to do such matches with multiple files, spanning subdirectories etc, so get to know find/xargs, and you can combine the two. A simple example of say changing the subnet in a bunch of .cfg files could be:

find -name '*.cfg' -print0 | xargs -0 -I {} sed -ie 's/\(192.168\)\.1/\1\.7/' {}

Note the -print0/-0 args to find/xargs (very useful for paths/filenames with spaces), and that you have to escape the capturing brackets because of the shell (same in sudo's example)

How about something like:

#!/bin/bash

addr=$1
port=$2
user=$3

sed -i -e "s/\(address=\).*/\1$1/" \
-e "s/\(port=\).*/\1$2/" \
-e "s/\(username=\).*/\1$3/" xyz.cfg

Where $1,$2 and $3 are the arguments passed to the script. Save it a file such as script.sh and make sure it executable with chmod +x script.sh then you can run it like:

$ ./script.sh 127.8.7.7 7822 xyz_ITR4

$ cat xyz.cfg
group address=127.8.7.7
port=7822
Jboss username=xyz_ITR4

This gives you the basic structure however you would want to think about validating input ect.