Check that an executable exists on the $PATH

When writing a vim plugin interacting with different programs on the server might be necessary. For instance you might want to use ruby to make a network request or perform some file management. But first, the vim plugin should check to see if the program ruby exists which can be accomplished with the executable() vimscript function.

:echo executable('ruby')
1

:echo executable('doesnotexist')
0

This can be used in a condition before running the ruby command.

if executable('ruby')
  system('ruby -e "puts YAML"')
endif