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From: Kaz Kylheku <480-992-1380@kylheku.com>
Newsgroups: comp.compilers
Subject: Re: Do people create parsers for command line arguments?
Date: Fri, 29 Jul 2022 20:52:04 -0000 (UTC)
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On 2022-07-28, Roger L Costello <costello@mitre.org> wrote:
> Hi Folks,
>
> I've seen some tools with pretty complicated arguments. The argument list is a
> language unto itself.
>
> Do people create parsers for command line arguments? Or is a parser overkill?

It happens.

You probably know these examples.

The find utility has an expression syntax whose tokens are command line
arguments. Parentheses are used for overriding precedence; they must be
escaped in common shell languages, so they are passed through to find
verbatim:

  find /etc \( -name '*.conf' -o -name '*.xml \) -exec command {} \:

The [ command also parses expressions that are individual arguments:

  if [ $foo = $bar -o $n1 -gt $n2 ] ; then ...

The tcpdump utility uses command line arguments as the tokens for
pcap filter expressions. (Sort of). Example from man page:

       To print traffic between helios and either hot or ace:

              tcpdump host helios and \( hot or ace \)

However, tcpdump can do its own splitting; the expression can be
quoted as one argument.

All of these programs must be parsing. They have phrase structures
and operator precedence with parentheses right the command line.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal