UNIX for Beginners Questions & Answers

Hi folks.

I'm a programmer of too many years to mention, but I'm only just starting my journey into unix based systems. I'm staring out with the Raspberry pi as they're inexpensive and have the built in GPIO which is always good fun. It's running the default Raspbian system.

Unix scripting is completely new to me, while I'm geo'll run atting used to it slowly I'm struggling with one problem, I'm not even sure if it's the right thing to do.

I want to change settings in a conf file. Example:

Code:

A Setting=5
Another Setting=15
The Last Setting=42

I'll run a sh to change Another Setting to 27.


Now, I can achieve this in two ways, I can have a bunch of files with different settings and rename/copy the one I want at the time. Or I can search the file and change the setting. The second is the preferred method as it's much more flexible.

How practical is it to write script that will search a file for settings and change them? Is parsing files something that's often done with scripts, if so, what commands do I need to get acquainted with? Or do people jump to python or other methods for such things?

All input welcome.
Thanks.

Moderator's Comments:

Please use CODE tags as required by forum rules!

Welcome to the forum.

*nix systems have a wealth of tools to process text files including all sorts of config files. Tools comprise sed, awk, perl to edit files, but also cut, paste, fold to dissect and reassemble them. This is only a short list of examples. On top, many modern shells are progammable and you can cobble a quick band aid script together to do for you what you need.

With shell builtins (no external command awk, sed, perl)
here is a standard procedure

Code:

fn="file.conf"
# split on =, change the certain value, write to .new file:
while IFS="=" read key val
do
  case $key in
  "Another Setting") val=27;;
  esac
  printf "%s\n" "$key=$val"
done < $fn > $fn.new
# If successful
if [ $? -eq 0 ]
then
  # copy back to the original file; if successful delete the .new file
  cp $fn.new $fn &&
  rm $fn.new
fi