Re: Do people create parsers for command line arguments?

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

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