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I’m writing some code in ruby, and I want to test for the presence of a command before the launch of the program. If the command isn’t installed, I want to display an error message and quit the program. So right now, I’m doing this.
puts `type -P spark &>/dev/null && continue || { echo "You must install spark"; exit 0; } `
So, everything works fine, BUT, the “exit 0” isn’t, and I can’t figure out why.
Do you have any idea to fix this? Or even better, is there another way to do it?
The reason you’re not exiting your script is that the call to exit is within the backticks. It’s exiting the subshell called to run spark, but that’s not the process interpreting your ruby script.
You could check the contents of the $? variable, which returns Process:Status for the backtick command after the command has been run.
As Daniel Pittman has suggested, however, it would be easier to check that the executable was available using something like FileTest. However, you probably want to couple that with a test of the return value, in case some other, more complex, failure occurs.