Bash Parameter Expansion

Filename or current running script

Somtimes it is useful to get the filename (basename) of the current running script. Example:

#!/usr/bin/env bash

usage () {
	cat <<EOF


  ${0##*/} OPTIONS


$0 expands to the full path of the current script. Using bash’s parameter expansion, it is possible to drop the path part and leav only the filename:

$ val=./src/lib/math.h

$ echo "$val"

$ echo "${val##*/}"

Use contents of file as part of string

Imagine this commit:

$ git commit -m 'Update .nvmrc with version ???'

Damn it! Forgot the version. Maybe I open another shell and cat the contents of the file, or stop this command line to do that in “this” shell session?

Or maybe we learn to use the features of the tools at our disposal‽

Test like this:

$ echo "Test: $(sed '' .nvmrc') end"
Test: v18.12.1 end

Added “end” just to see if the result would be on a single line. It is! We are ready to commit our changes.

$ git commit -m "Update .nvmrc with node $(sed '' .nvmrc)"

The result will be something like:

$ git add .nvmrc

$ git commit -m "Update .nvmrc with node $(sed '' .nvmrc)"
[devel f7144a7] Update .nvmrc with node v18.12.1
 1 file changed, 1 insertion(+), 1 deletion(-)

$ git log -1
commit f7144a77830ec39d186a72e5629c143adf9c8f2b (HEAD -> devel)
Author: Aayla Secura <>
Date:   Sun Nov 6 07:16:17 2022 -0300

    Update .nvmrc with node v18.12.1

remove newline

Similar to tr -d '\n, we can also do in pure bash: