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This question is somewhat similar to this: Unix/Linux command syntax

Suppose I have a program foo that takes arguments -a and -b. If both a and b take a string argument what is the meaning of this

foo -b -a bar

If multiple b:s are allowed

foo -b -a -b


Is there a true specification of the command line syntax somewhere?

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up vote 4 down vote accepted

Unless you can find something that says option arguments can't start with a minus sign, then the only possible interpretation is


See also: POSIX Utility Conventions.

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So I need to know if the option takes an argument or not, otherwise it will be impossible to know what it is. – user877329 Sep 4 '12 at 15:01
Yes, that's my understanding. – Mikel Sep 4 '12 at 15:41
@user877329 See also the getopt function and the getopts utility. Most C programs use getopt (or a some extension of it that allows options to be more than one letter long, such as GNU getopt_long) and most shell scripts use getopts. – Gilles Sep 4 '12 at 22:14

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