Leonid Shevtsov Leonid Shevtsov - 6 months ago 9
Ruby Question

How to parse an argument without a name with Ruby's optparse

I need to parse a command line like

script.rb <mandatory filename> [options]


with optparse.

Sure I can write some custom code to handle the filename, then pass
ARGV
to optparse, but maybe there's a simpler way to do it?

EDIT: there's another hacky way to parse such a command line, and that is pass
['--mandatory-filename'] + ARGV
to optparse, then handle the
--mandatory-filename
option.

Answer

First parse! with optparse, then scan the ARGV and raise if ARGV is empty. Like so:

op.parse!
filename = ARGV.pop
raise "Need to specify a file to process" unless filename

The mandatory filename will not be processed by the OptionParser and will be left for you in ARGV - if it's not there, just raise manually.

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