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Full Discussion: getopts problem
Top Forums UNIX for Advanced & Expert Users getopts problem Post 302257408 by bakunin on Wednesday 12th of November 2008 04:53:28 AM
Old 11-12-2008
Quote:
Originally Posted by mobydick
----according to yoy the envirinment [$1..$2..] will change if i call from the same shell but here it is printing the same values.
The point is not that it has to change, but it might change. You simply cannot rely on the fact that "$1" remains the same before and after getopts - whereas you can rely on, say, "$charley" being the same before and after executing a command.

The meaning of the set-command is simple: "set --" clears the special variables "$1", "$2", etc.:

Code:
# cat settest.sh
#!/bin/ksh

echo "first parm is: $1"
echo "second parm is: $2"
echo "third parm is: $3"

set --

echo "first parm is: $1"
echo "second parm is: $2"
echo "third parm is: $3"
exit 0

# ./settest.sh a b c
first parm is: a
second parm is: b
third parm is: c
first parm is:
second parm is:
third parm is:

Therefore the "set -- -2-------" means: first make sure no other commandline parameter is set, regardless of what you enter on the commandline, then set exactly one parameter ("-2") with some argument ("------").

I hope this helps.

bakunin
 

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LEARN ABOUT LINUX

putctl

putctl(9F)						   Kernel Functions for Drivers 						putctl(9F)

NAME

       putctl - send a control message to a queue

SYNOPSIS

       #include <sys/stream.h>

       int putctl(queue_t *q, int type);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       q	Queue to which the message is to be sent.

       type	Message type (must be control, not data type).

DESCRIPTION

       putctl()  tests the  type argument to make sure a data type has not been specified, and then attempts to allocate a message block. putctl()
       fails if  type is  M_DATA, M_PROTO, or  M_PCPROTO, or if a message block cannot be allocated. If successful,  putctl() calls  the   put(9E)
       routine of the queue pointed to by  q with the newly allocated and initialized messages.

RETURN VALUES

       On success,  1 is returned. If  type is a data type, or if a message block cannot be allocated, 0 is returned.

CONTEXT

       putctl() can be called from user or interrupt context.

EXAMPLES

       Example 1: Using putctl()

       The   send_ctl()  routine  is  used to pass control messages downstream. M_BREAK messages are handled with  putctl() (line 11). putctl1(9F)
       (line 16) is used for  M_DELAY messages,  so that  parm can be used to specify the length of the delay. In either case, if a message  block
       cannot be allocated  a  variable recording the number of allocation failures
	is incremented (lines 12, 17). If an invalid message type is detected,	cmn_err(9F) panics the system (line 21).

	1  void
	2  send_ctl(wrq, type, parm)
	3      queue_t *wrq;
	4      uchar_t type;
	5      uchar_t parm;
	6  {
	7	  extern int num_alloc_fail;
	8
	9	switch (type) {
       10	  case M_BREAK:
       11	      if (!putctl(wrq->q_next, M_BREAK))
       12		       num_alloc_fail++;
       13		break;
       14
       15	case M_DELAY:
       16	      if (!putctl1(wrq->q_next, M_DELAY, parm))
       17		       num_alloc_fail++;
       18	      break;
       19
       20	default:
       21	      cmn_err(CE_PANIC, "send_ctl: bad message type passed");
       22		break;
       23	  }
       24  }

SEE ALSO

       put(9E), cmn_err(9F), datamsg(9F), putctl1(9F), putnextctl(9F)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.10							    11 Apr 1991 							putctl(9F)
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