Having installed Powershell 6.0 Core on our linux agents, there is no longer a program called "powershell". It is called "pwsh", and as such anything calling "powershell" will fail.

Example:

Fails:

sh('powershell -version')

Works:

sh('pwsh -version')

A workaround is to make a symbolic link between pwsh -> powershell.

ln -s /usr/bin/pwsh /usr/bin/powershell