======Synopsis:======
[[set]] shell [<program>]

======Description:======
When the [[exec command|EXEC]] command is used, the program named in
this variable is spawned to execute the desired command.  This is
generally a command shell of some sort, though it doesn't necessarily
have to be one.

If the shell requires special command-line switches, they may be given
in the [[set shell_flags|SHELL_FLAGS]] variable.