With Ruby: how can I test to see if a linux command is available without returning the output of the-CodePudding

I'm using Ruby on Linux. I'd like to test for the existence of a command on the Linux system.

I'd like to not get back the output of the command that I'm testing for.

I'd also like to not get back any output that results from the shell being unable to find the command.

I want to avoid using shell redirection from within the command that I send to the shell. So something like system("foo > /dev/null") would be unsuitable.

I'm ok with using redirection if there is a way to do it from Ruby.

CodePudding user response：

The simplest thing would be just to use system. Let's say you're looking for ls.

irb(main):005:0> system("which ls")
/bin/ls
=> true

If that's off the table, you could peek into the directories in ENV["PATH"] for the executable you're looking for. ENV["PATH"].split(":") would give you an array of directory names to check for the desired command. If you find a file with the right name, you may want to ensure it's an executable.

CodePudding user response：

I want to avoid using shell redirection from within the command that I send to the shell. So something like system("foo > /dev/null") would be unsuitable. I'm ok with using redirection if there is a way to do it from Ruby.

system("exec which cmd", out: "/dev/null")
puts "Command is available." if ($?).success?

The exec is to explicitly avoid unnecessary forking in the shell.

As a sidenote type -P can be used instead of which, but it relies on Bash and may have surprising effects if script is ported to an environment with a different default shell.