List PID And Name Of Current Shell Process

In Julia Evans' How to add a directory to your PATH, she shows off an odd-looking command for determining what shell (e.g. bash or zsh) you are currently running.

$ ps -p $$ -o pid=,comm=

38105 -zsh

I already know I'm running zsh, but I thought this command was interesting enough to dig into and break down.

• The ps command lists processes that "have controlling terminals"
• The $$ is a special shell variable representing the PID of the current process (try echo $$)
• The -p flag allows you to specify a PID for ps to grab, in this case, the $$ PID
• The -o flag allows us to specify the output format, such as the PID and command name
• The = after pid and comm tell ps to exclude headers from the output

Additionally, I noticed that it output -zsh (not just zsh). That leading hyphen seems to indicate that this zsh process is a login shell. That means it was the process used to initiate an interactive shell session and something like the .zprofile would have been sourced as part of that.