Getting output of system() calls in ruby

Question

If I call a command using system() in ruby, how do I get it's output?

e.g.

system("ls")

Answer 1

You use backticks:

`ls`

Answer 2

You may want to have a look at this thread in comp.lang.ruby

Answer 3

Another way is:

f = open("|ls")
foo = f.read()

Note that's the "pipe" character before "ls" in open. This can also be used to feed data into the programs standard input as well as reading its standard output.

Answer 4

I'd like to expand & clarify chaos's answer a bit.

If you surround your command with backticks, then you don't need to (explicitly) call system() at all. The backticks execute the command and return the output as a string. You can then assign the value to a variable like so:

output = `ls`
p output

Answer 5

I found that the following is useful if you need the return value:

result = %x[ls]
puts result

I specifically wanted to list the pids of all the Java processes on my machine, and used this:

ids = %x[ps ax | grep java | awk '{ print $1 }' | xargs]

Answer 6

As a direct system(...) replacement you may use Open3.popen3(...)

Further discussion: http://tech.natemurray.com/2007/03/ruby-shell-commands.html

Answer 7

just for the records, if you want both (output and operation result) you can do:

output=`ls no_existing_file` ;  result=$?.success?