How to parse an argument without a name with Ruby's optparse
Solution 1
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.
Solution 2
Just to follow up on what Julik and Shadowfirebird said: When parsing with OptionParser
be aware that parse!
and parse
have different functionality. The former will remove every argument it understands out of the passed array where the latter will leave them be. This changes your conditions for determining if the required argument is present.
Solution 3
Although it doesn't apply to every situation, it is often nice to be able to process multiple files on a single command line, such as:
script.rb [options] file1 file2 ...
file1 is mandatory, but file2 and beyond is optional.
The best way I know to do this follows this convention:
options = {}
optparse = OptionParser.new do |opts|
opts.banner = "Usage: script.rb [options] file1 file2 ..."
opts.on('-a', '--an-option ARG', 'Set some option') do |arg|
options[:a] = arg
end
...
end
optparse.parse!
# Check required conditions
if ARGV.empty?
puts optparse
exit(-1)
end
If files are not provided, a help message will be displayed with the usage banner and a description of options. If the files are present, they will be the only thing left in ARGV.
Solution 4
I am not sure if it was added recently, but none of the previous answers mention that optparse.parse
will return the ARGV value after removing the parsed options.
If you do this:
rest = optparse.parse!
You will get an array with the given file/s (along unknown options). This way you do not have to care if the options come before or after the file.
Leonid Shevtsov
Ruby, Javascript, React, React Native, Golang, Elixir, Clojure developer. Personal site: https://leonid.shevtsov.me Github: https://github.com/leonid-shevtsov
Updated on June 24, 2022Comments
-
Leonid Shevtsov almost 2 years
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. -
PJP over 13 yearsOptParse handles all sorts of options. It does flags, parameters, optional parameters, lists, booleans. See the Complete example for more info.
-
sschuberth over 8 yearsUse something like
op.banner += ' <mandatory filename>'
to adjust theUsage:
line accordingly. -
nhed about 7 yearswouldn't
ARGV.shift
instead ofARGV.pop
be better if we wanted to expand to multiple required params? -
Greg Schmit over 6 yearsnhed, yeah good idea since first one or two positional arguments are usually required and latter ones are optional (like how with
zip
you first have to put the filename for the archive, and then a list of files that get zipped into the archive).