Variables defined in for-loops are accessible from callbacks for `exec` function, however, contents of those variables change as the loop progresses and updates the variable.

good.coffee

# Use Underscore lib to wrap each loop in a func.

exec = require('child_process').exec
_ = require('underscore')._

some_list = [1,2,3]

_.each some_list, (i) ->
  exec "ls", (err, stdout, stderr) ->
    console.log i

# The result is always
#
# 1
# 2
# 3

Not_good.coffee

exec = require('child_process').exec

some_list = [1,2,3]

for i in some_list
  exec "ls", (err, stdout, stderr) ->
    console.log i

# The result is NOT always
#
# 1
# 2
# 3
#
# It might even be
#
# 3
# 3
# 3