Bash Scripts

Run Script from STDIN

Introductory Example

You have this script:

$ cat ./
printf '%s\n' "$1"

Note it takes one parameter which is passed to printf. It can be called like this:

$ bash ./ hello

But there are situations which require the script to be run from STDIN. Then, to pass the parameter, these are possible:

$ cat ./ | bash -s - hello

$ bash -s - hello < <(cat ./

GPG-Encrypted Script

For example, it may be necessary to run a script from STDIN when we want to decrypt and run it “on the fly”, without first saving it to a plain, unencrypted file:

First, say we encrypt our script with gpg:

gpg \
  --no-symkey-cache \
  --symmetric \
  --output ./ \

And then, we need to run it from the encrypted file. Again, both of these approaches work:

$ bash -s - 'It works!' < <(gpg -dq ./
It works!

$ gpg -dq ./ | bash -s - 'Once again!'
Once again!

Depending on how GnuPG and/or gpg-agent is set up on your computer, you may or may not be prompted for passwords at any given time.

It may be necessary to prevent errors or warning messages to be sent to STDOUT, which would make the script text invalid. Maybe, something like this:

$ 2> /dev/null gpg -dq ./ | bash -s - 'Once again!'
Once again!

Other Cases

This is also quite useful over ssh. Send your script to remote, read back its output

gpg -dq ./script.gpg 2>/dev/null | bash -s -- <args...>