RE: command line arguments

["Stone, Joshua I" <joshua dot i dot stone at intel dot com>]

Frank Ch. Eigler wrote:
> Hi -
> 
> I committed a draft of command line argument support as per bug #1304.
> One part (plain substitution into scripts) is usable now.  Another
> part (initializing globals at module init time) is sort of dormant.
> 
> The way the first part works is by making any additional arguments
> passed to "stap" available to the script for substitution as string
> or number literals:
> 
> # stap -e 'probe kernel.function(@1) { print($2) }' sys_open 4

Very cool!
 
> The @ vs $ distinction encodes whether the numbered argument should be
> pasted as a string or number literal.  I considered guessing but
> heuristics don't seem to belong somewhere so critical.
> 
> I'm open to suggestions about better notation than $n and @n.  (#n is
> out because of comments; % and others because of arithmetic
> operators.) 

It would indeed be nice if $N could be dynamically be typed, especially
since the other $target variables are, but I can see how this would be
hard.

The @ is ok, but it doesn't really say "string" to me.  Perhaps a
single-quote or backquote might be better - '1 or `1?

Another option is to allow expansion of $N within string literals - then
if you want a string you use "$N" and for a number use just a plain $N.
Then your toy command-line would be:

# stap -e 'probe kernel.function("$1") { print($2) }' sys_open 4

And you could still do error checking...

# stap -e 'probe kernel.function("$1") { print($2) }' sys_open foo
ERROR: got a string argument where a number was expected (argument 2)


Josh