Bash and PowerShell in a single script file

I’m not saying it’s all dotnet’s fault, but it was when deploying dotnetcore services to a linux VM that I thought, “what I really, really want is both bash and powershell setup scripts in a single file”. Surely a working incantation can be crafted from such arcane systems of quoting and escaping as the two languages offer?

½ an evening later :

# This file has a bash section followed by a powershell section,
# and a shared section at the end.
echo @'
' > /dev/null
#vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
# Bash Start --------------------------------------------------

scriptdir="`dirname "${BASH_SOURCE[0]}"`";
echo BASH. Script is running from $scriptdir

# Bash End ----------------------------------------------------
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
echo > /dev/null <<"out-null" ###
'@ | out-null
#vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
# Powershell Start --------------------------------------------

$scriptdir=$PSScriptRoot
"powershell. Script is running from $scriptdir"

# Powershell End ----------------------------------------------
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
out-null

echo "Some lines work in both bash and powershell. Calculating scriptdir=$scriptdir, requires separate sections."

It relies on herestring quoting being different for each platform, as is the escape character ( \ vs ` ). Readibility (ha!) is very much helped by

#comments begin with a hash 

being common to both, so I can do visible dividers between the sections.

My main goal was environment variable setup before launching dotnetcore services. Sadly the incompatible syntaxes for variables and environment:

#powershell syntax
$variable="value"
$env:variable2=$value
#bash syntax
variable=value
export variable2=value 

means very little shared code inside the file, but it really cut down errors a lot just by having them in the same file. Almost-a-single-source-of-truth turned out to be much more reliable than not-at-all a single source of truth.

Bash-then-powershell was simpler than Powershell-then-bash. My state-of-the art is powershell named and validated parameters, which allows tab-completion to work in powershell.

` # \
# PowerShell Param
# every line must end in #\ except last line must end in <#\
# And, you can't use backticks in this section        #\
param( [ValidateSet('A','B')]$tabCompletionWorksHere, #\
       [switch]$andHere                               #\
     )                                               <#\
#^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `

Repo: github.com/chrisfcarroll/PowerShell-Bash-Dual-Script-Templates

Raw: Powershell-or-bash-with-parameters .

Alternatively, do everything in powershell?

Of course, sensible people would do everything in a single scripting language. But it has been well-worth having the tools for both approaches. Especially for short bootstrap scripts.

For a powershell core everywhere approach, my main adaptation is the shebang header on all .ps1 files:

#! /usr/bin/env pwsh

which tells unix machines to what kind of script it is. Powershell itself ignores it as a comment. Finally, you must also chmod a+x *.ps1 to mark them as executable.

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