Time for my once-yearly blog post! This time, I'd like to post a tip when working on Bash scripts, and when you do, caring about STDOUT and STDERR is important as a responsible programmer. Let's take an example script, such as:
#!/usr/bin/env bash
set -xeou pipefail
echo "this should be stdout"
echo "this shoudl be stderr" >&2
If you run this as is, you should see something like:
$ ./t.sh
+ echo 'this should be stdout'
this should be stdout
+ echo 'this shoudl be stderr'
this shoudl be stderr
There's no visual difference between the output when reading it as a human. Well, there is a way to improve this, to
help work on the script to ensure your stdout/stderr is being written appropriately. Simply append this little bit of
redirection + sed magic, 2> >(sed 's/^/e: /') > >(sed 's/^/o: /'), to your command, such as:
$ ./t.sh 2> >(sed 's/^/e: /') > >(sed 's/^/o: /')
o: this should be stdout
e: + echo 'this should be stdout'
e: + echo 'this shoudl be stderr'
e: this shoudl be stderr
Notice how also, because I had set -x, the trace lines are also shown in the stderr stream. Naturally, this technique
will need sed installed. Enjoy!