“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

def command?(name)
  `which #{name}`
  $?.success?
end

Initially taken from hub, which used type -t instead of which though (and which failed for both zsh and bash for me).

Answer 2

Not so much elegant but it works :).

def cmdExists?(c)
  system(c + " > /dev/null")
  return false if $?.exitstatus == 127
  true
end

Warning: This is NOT recommended, dangerous advice!

Answer 3

There was a GEM called which_rubythat was a pure-Ruby which implementation. It's no longer available.

However, I found this pure-Ruby alternative implementation.

Answer 4

On linux I use:

exists = `which #{command}`.size.>(0)

Unfortunately, which is not a POSIX command and so behaves differently on Mac, BSD, etc (i.e., throws an error if the command is not found). Maybe the ideal solution would be to use

`command -v #{command}`.size.>(0)  # fails!: ruby can't access built-in functions

But this fails because ruby seems to not be capable of accessing built-in functions. But command -v would be the POSIX way to do this.