Bash Substitution Cheatsheet

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Took forever for me to understand the purpose of Bash # and % substitutions - they are immensely useful for string manipulation in your scripts. Largely because I had to look them up each time I needed to use them.

First, as a key to remembering how they operate, they both REMOVE part of the variable value; either from the beginning of the string or the end of the string.

To remember which is which, on my keyboard (and here I'll say my keyboard layout as United States which may not be helpful to other keyboard layouts) # (Shift 3) is to the left of % (Shift 5) on my keyboard so I use this to remember which is which:

# cuts from the beginning of the string
% cuts from the end of the string

And you supply a pattern to match to remove.

Where do I use this? A simple search of Zesk Build code shows:

Faster `dirname`

Any file path, do:

parentDirectory="${filePath%/*}"

To do dirname but faster. (No subshell)

Remove directory trailing slash

Ensure your paths concatenate cleanly:

home=${home%/}

Ensure single slash separates paths

If you don't want to modify the path for reasons:

newPath="${currentPath%/*}/$fileBase"

Easy file extensions removal:

Remove a file extension:

while read -r name; do printf "%s\n" "${name%.sh}"; done < <(find . -name '*.sh')