TCL: use "help" option from cmdline package

In my TCL script I am trying to provide input argument which will be parsed using 'cmdline' package. I have defined the following in my script:

set run_options {
{input_1.arg 8 "first input argument"}
{input_2.arg 1 "second input argument"}
{msb  "choose it if input data has msb first"}
{lsb  "choose it if input data has lsb first"}
}
set my_usage ": \n tclsh my_src \[options] ...\noptions are:"

if {[catch {array set params [::cmdline::getoptions argv $run_options $my_usage]} msg]} {
 puts "Error while parsing user options of $msg"
 exit 1

}

everything look fine except that when running my script I figured out that the 'cmdline' package defines "help" option by default, but when I run my script with "-help" option the following is the output:

Error while parsing user options of my_src : 
 tclsh my_src [options] ...
options are:
 -input_1 value       first input argument <8>
 -input_2 value       second input argument <1>
 -msb                 choose it if input data has msb first
 -lsb                 choose it if input data has lsb first
 --                   Forcibly stop option processing
 -help                Print this message
 -?                   Print this message

so, does anyone know how to use this automatically added "help" option without giving error message?

Solution

cmdline::getoptions doesn't differentiate between -help and an unknown option (An unrecognized option is treated like it was -?). If you want to have different messages for the two cases, you need to use one of the the lower level functions directly in a loop, or something like the following enhanced version of cmdline::getoptions:

#!/usr/bin/env tclsh
package require try ;# In case you're still using tcl 8.5 for some reason
package require cmdline 1.5

proc better_getoptions {arglistVar optlist usage} {
    upvar 1 $arglistVar argv
    # Warning: Internal cmdline function
    set opts [::cmdline::GetOptionDefaults $optlist result]
    while {[set err [::cmdline::getopt argv $opts opt arg]]} {
        if {$err < 0} {
            return -code error -errorcode {CMDLINE ERROR} $arg
        }
        set result($opt) $arg
    }
    if {[info exists result(?)] || [info exists result(help)]} {
        return -code error -errorcode {CMDLINE USAGE} \
            [::cmdline::usage $optlist $usage]
    }
    return [array get result]
}

set run_options {
    {input_1.arg 8 "first input argument"}
    {input_2.arg 1 "second input argument"}
    {msb  "choose it if input data has msb first"}
    {lsb  "choose it if input data has lsb first"}
}
set my_usage ": \n tclsh my_src \[options] ...\noptions are:"

try {
    array set params [better_getoptions argv $run_options $my_usage]
    puts "All options valid"
} trap {CMDLINE USAGE} {msg} {
    puts stderr $msg
    exit 0
} trap {CMDLINE ERROR} {msg} {
    puts stderr "Error: $msg"
    exit 1
}

Example usage:

$ ./example.tcl --help
cmd : 
 tclsh my_src [options] ...
options are:
 -input_1 value       first input argument <8>
 -input_2 value       second input argument <1>
 -msb                 choose it if input data has msb first
 -lsb                 choose it if input data has lsb first
 --                   Forcibly stop option processing
 -help                Print this message
 -?                   Print this message
$ ./example.tcl -foo
Error: Illegal option "-foo"
$ ./example.tcl -input_1
Error: Option "input_1" requires an argument
$ ./example.tcl -msb
All options valid