"source" in ruby subshells

Question

I need to run a shell command from a ruby application. I'm using system() but this also applies to backticks.

When running my command, I need to load a shell script first that sets up some things so I try something like this:

system("source my_script.sh && my_command")

On my Mac laptop this works as intended but on my ubuntu server I get:

sh: 1: source: not found

I was wondering about the "sh" in there since my shell should be a bash, so tried this:

system("echo $SHELL && source my_script.sh && my_command")

Which gives me:

/bin/bash
sh: 1: source: not found

So, it is using the right shell but for some reason, source does not work.

Why? And what can I do about it?

Update As Sergio Tulentsev pointed out, Ruby does not necessarily use the shell that is set in $SHELL.

This gave me the actual shell that ruby was using:

system("ps -p $$ | tail -1 | awk '{print $NF}'")
sh
 => true

So, it's using sh. Can I somehow force it to use bash?

If $SHELL is set to bash, it doesn't necessarily mean that ruby will use it, I think. Try this tip to determine actual shell: liquidat.wordpress.com/2007/07/28/… — Sergio Tulentsev
– Sergio Tulentsev, Commented Mar 25, 2014 at 9:41
Oh, I didn't know that. But yes, it's actually "sh". Thanks. — selfawaresoup
– selfawaresoup, Commented Mar 25, 2014 at 9:44
If $SHELL is sh, then source wont work, you'll need to de . file.sh to source it — jbr
– jbr, Commented Mar 25, 2014 at 9:49

jbr · Accepted Answer · 2014-03-25 09:51:56Z

2

You need to try adding ./ in front of the file you want to source, that should work if the subshell is bash (check $SHELL).

irb(main):003:0> system("source ./test.sh && echo $TEST && cat test.sh")
test
export TEST=test
=> true

If $SHELL is sh, then you need to do . ./test.sh instead of source ./test.sh, as the source keyword is bash only.

Or you can make sure that you are using bash, by doing:

irb(main):007:0> system("/bin/bash -c 'source ./test.sh && echo $TEST && cat test.sh'")
test
export TEST=test
=> true

edited Mar 25, 2014 at 9:51

answered Mar 25, 2014 at 9:42

jbr

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3 Comments

selfawaresoup Over a year ago

Nope, that's not it. Even with absolute paths it doesn't work.

selfawaresoup Over a year ago

Thanks, that kind of works but brings me to escaping problems with my command string. I think I'll spawn /usr/bin/env bash with Open3 to have finer control over it.

jbr Over a year ago

That sounds like a good idea. As for the escaping, you should probably wrap you Open3 call, so it takes care of that.

selfawaresoup · Accepted Answer · 2014-03-25 10:16:16Z

1

As others have pointed out, Ruby uses sh for its subshells. One way to make it use bash would be something like system("/bin/bash -c '...'") which leads to all kinds of escaping problems. Instead I decided to use Open3 to spawn a "real" process, run bash in it and pipe my commands into it. Works like a charm:

require "open3"

# using bash --login to ensure the same env as usual
Open3.popen3('/usr/bin/env bash --login') do |stdin, stdout, stderr, wait_thr|
  pid = wait_thr[:pid]

  stdin.puts("cd some_directory")
  stdin.puts("source some_script")
  stdin.puts("some_command")

  # don't forget to close it again
  stdin.puts("exit")

  # for debug purposes
  stdout.each_line do |line|
    puts "STDOUT: " + line
  end

  stdin.close
  stdout.close
  stderr.close
end

This may seem like a little overkill but the control it allows over the child process is actually pretty nice.

Thanks everybody for your suggestions.

answered Mar 25, 2014 at 10:16

selfawaresoup

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1 Comment

yerforkferchips Over a year ago

You make a good point about the escaping problems. But the code you show also exhibits those escaping problems, doesn't it? I don't see how I can have the safe escaped command syntax via arrays when all I'm doing is putting commands on stdin. Maybe I'm missing something here.

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