I learned about the call command in Windows recently.

Some context – was trying to run a command via HPSA at a customer, but kept getting an error that the program was not a recognized internal or external command.

Very frustrating.

Then one of the guys I worked with suggested adding a “call” to the front of my script. That worked like a champ. Here’s why.

When the HPSA Agent on a Managed Server receives a script to run from the Core, it runs it in a headless terminal session. This means that while environment variables (eg %ProgramFiles%) expand properly, if the first part of the command is NOT a built-in from cmd.exe, it won’t execute. Unlike *nix which is designed to run most things headless, Windows never was (and isn’t still as of Win2k8R2).

The built-in command ‘call‘ forks the next command to a full session (albeit still headless), and enables cmd.exe to run it properly.

Now you know.