docs/data/reusables/actions/supported-shells.md

Supported platform	shell parameter	Description	Command run internally
Linux / macOS	unspecified	The default shell on non-Windows platforms. Note that this runs a different command to when bash is specified explicitly. If bash is not found in the path, this is treated as sh.	bash -e {0}
All	bash	The default shell on non-Windows platforms with a fallback to sh. When specifying a bash shell on Windows, the bash shell included with Git for Windows is used.	bash --noprofile --norc -eo pipefail {0}
All	pwsh	The PowerShell Core. {% data variables.product.prodname_dotcom %} appends the extension .ps1 to your script name.	pwsh -command ". '{0}'"
All	python	Executes the python command.	python {0}
Linux / macOS	sh	The fallback behavior for non-Windows platforms if no shell is provided and bash is not found in the path.	sh -e {0}
Windows	cmd	{% data variables.product.prodname_dotcom %} appends the extension .cmd to your script name and substitutes for {0}.	%ComSpec% /D /E:ON /V:OFF /S /C "CALL "{0}"".
Windows	pwsh	This is the default shell used on Windows. The PowerShell Core. {% data variables.product.prodname_dotcom %} appends the extension .ps1 to your script name. If your self-hosted Windows runner does not have PowerShell Core installed, then PowerShell Desktop is used instead.	pwsh -command ". '{0}'".
Windows	powershell	The PowerShell Desktop. {% data variables.product.prodname_dotcom %} appends the extension .ps1 to your script name.	powershell -command ". '{0}'".