Polyglot PowerShell and bash script

I wanted to put some bash and some PowerShell into the same script file, so if I ran it in bash it would do one thing, and if I ran in PowerShell it would do something else. Here’s what I came up with:

#!/bin/bash
echo `# <#`

# Bash goes here
set -euo pipefail

ls -al doing bash stuff

exit
#> > $null

# PowerShell goes here

$val = (
    'powershell',
    'stuff',
    'here'
)

foreach($v in $val) {
    # yadda yadda
}

The magic is here:

echo `# <#`
# bash code
exit
#> > $null
# powershell code

On bash, it executes what’s between the backticks, which is just a comment. So it succeeds silently and passes through to the bash script. We exit before it gets to any PowerShell syntax.

On PowerShell the backtick is an escape character, so `# is parsed as the string "#". It’s followed by a multiline comment delimited by <# #>, so PowerShell skips over all our bash code. We redirect to $null to suppress the echoed #.