My First Sed Script (That Became a Bash Script?)

Last post, I wrote about a Sed script I wrote to help me switch configurations. As always, I’ve learned a little in the meantime, and I’ve updated the script to reflect that. As a result, it’s not a Sed script anymore, but a Bash script that calls on Sed directly to perform tasks.

I noticed that I was not being very efficient. For one, I created three files to do something that could be done in one. For another, two of those files (the Sed scripts) were virtually identical, with only two words being changed in four instances. When saw what I had done, I was reminded of a thing I read somewhere, but sadly cannot recall where:

If you’re doing something more than once, you’re not using a computer correctly.

Anonymous?

It’s a little provocative, of course, but I like the central idea of it. A computer is meant to automate tasks, and if you, the human user, are repeatedly performing the same task, surely you should let the computer handle that? Furthermore, there’s an added risk of error: I could edit one file and forget to edit the others to match. Or, of course, were I to write a much, much larger program, copy-pasting the same code only leads to a less legible program in the end.

So, I figured to replace the repeated words with a variable, set in the Bash script, and that reduced the need for two separate Sed scripts. Now that I was down to just the one small script, I realized I could just put it directly in Bash. I would lose the Sed syntax highlighting in Vim (as it would be highlighting Bash), but to be fair the Sed highlights aren’t that great anyway. So, long story short, I ended up with the following, single script:

#!/bin/bash
# switch_config.sj -- Bash script to switch over i3wm configs
# $1 = switch argument

# Check what file to change
case $1 in
    -d|--desktop) to=Desktop
	    	  from=Laptop
		  ;;
    -l|--laptop)  to=Laptop
	    	  from=Desktop
		  ;;
    *) echo "Select either -d, --desktop, -l, or --laptop"; exit 1
	    	  ;;
esac

# Back up file, using \cp to avoid interactive alias
\cp config -f config.old

# Catch potential errors
if [ $# != 1 ]
	then echo "Error: please provide one argument."; exit 1
fi


echo "Swapping i3wm configuration over from $from to $to."

# Using sed, comment out one set, and uncomment the other
sed -i '
/# '"$from"'/,/^$/{
	/# '"$from"'/b
	/^$/b
	/^#/!s/\(.*$\)/\#\1/
}

/# '"$to"'/,/^$/{
	/# '"$to"'/!s/#//
}
' config

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