“which in ruby”: Checking if program exists in $PATH from ruby

Question

my scripts rely heavily on external programs and scripts. I need to be sure that a program I need to call exists. Manually, I\'d check this using \'which\' in the commandlin

Answer 1

Use MakeMakefile#find_executable0 with Logging Disabled

There are a number of good answers already, but here's what I use:

require 'mkmf'

def set_mkmf_log(logfile=File::NULL)
  MakeMakefile::Logging.instance_variable_set(:@logfile, logfile)
end

# Return path to cmd as a String, or nil if not found.
def which(cmd)
  old_mkmf_log = MakeMakefile::Logging.instance_variable_get(:@logfile)
  set_mkmf_log(nil)
  path_to_cmd = find_executable0(cmd)
  set_mkmf_log(old_mkmf_log)
  path_to_cmd
end

This uses the undocumented #find_executable0 method invoked by MakeMakefile#find_executable to return the path without cluttering standard output. The #which method also temporarily redirects the mkmf logfile to /dev/null to prevent cluttering the current working directory with "mkmf.log" or similar.