how can I pass a variable into a script from the command line?

Question

Let's say I'm running a script at the command line:

coffee ./scripts/doSomeStuff.coffee

where doSomeStuff.coffee looks like:

numberOfTimes = ??? 

doStuff = (times) -> 
  while times > 0 
    console.log('doing stuff') 
    --times 

doStuff(numberOfTimes)

How can I pass in the number of times to do stuff via the command line? --eval seemed like the obvious choice but adding --eval='global.numberOfTimes=5' didn't help.

I can do it with export REPEAT_TIMES=5 from bash but that seems rife with potential side-effects.

Alex Wayne · Accepted Answer · 2013-07-29 21:01:50Z

3

Same way you do with node.js, via process.argv

http://nodejs.org/docs/latest/api/process.html#process_process_argv

Command:

coffee ./scripts/doSomeStuff.coffee 5

CoffeeScript:

numberOfTimes = process.argv[2]
# index 0 is the interpreter: coffee
# index 1 is the file: ./scripts/doSomeStuff.coffee
# index 2 is the first argument: 5

There are also a great number of npm modules that provide nicer interfaces for parsing argv. I've had a good time with optimist myself.

edited Jul 29, 2013 at 21:01

answered Jul 29, 2013 at 20:46

Alex Wayne

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2 Comments

Alex Wayne Over a year ago

PLease don't insert code into other peoples answers. I don't want to look like I recommended your way of setting a default, because that's pretty convoluted. That should very simply be: numberOfTimes = process.argv[2] ? 1

jcollum Over a year ago

You're right I hadn't run that code yet, forgot about the simpler way. I think adding that makes a more complete answer though so I added it.

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