LinuxQuestions.org - How are arguments passed to a bash script?

I am using SNMP traps to pass information via snmp from a module on one system to a module on another system. Specifically, I am using SNMPv2 Notify messages, as described on this page:

http://www.net-snmp.org/wiki/index.p...ring_snmptrapd

Now, for reasons that are not at all clear to me, snmptrapd expects that the command that it invokes when it processes a trap will be a shell script.

I do not wish to use a shell script; I want to have snmptrapd invoke a dedicated C program that I will provide. This C program will accept the data that is being sent via the trap, and will forward that data via some IPC mechanism (I haven't decided yet...probably a TCP socket) to its ultimate destination.

I am correctly building the SNMP trap message in my C module, and sending it. The snmptrapd is properly processing it and invoking an appropriate command. When that command is the demo handler script as described on the net-snmp page (and reproduced here), everything works as expected and the output is correct (a text file in /tmp, for now).

When I replace that script with a dedicated C program, the result is not as desired; I am not picking up the trap information although the program is being invoked.

Specifically, here is the demo trap handler script I am using, from the net-snmp site:

Code:

 #!/bin/sh

 echo "executing script" >/tmp/mytstfile

 read host

 read ip

 vars=

 

 while read oid val

 do

  if [ "$vars" = "" ]

  then

    vars="$oid = $val"

  else

    vars="$vars, $oid = $val"

  fi

  vars="$vars ==spacer=="

 done

 

 echo trap: $1 tag1 $host tag2 $ip tag3 $vars >>/tmp/mytstfile

And here is my C program, which I would like to have do the same thing (output the same data, though the format might be different):

Code:

#include <stdio.h>

#include <stdlib.h>



int main(int argc, char *argv[])

{

int nn=0;

char *arg;

FILE *fp;

fp=fopen("/tmp/mytstfile","w");

fprintf(fp,"arg count is %s\n");

fclose(fp);

fp=fopen("/tmp/mytstfile","a+");

arg = argv[nn];

while(argv[nn] != NULL)

//while(nn < 5)

{

        fprintf(fp,"arg is %s\n",argv[nn]);

        nn++;

}

fclose(fp);

return 0;

}

Now, here is the text from /tmp/mytstfile after I invoke a trap with the shell script as the command:

Code:

executing script

trap: tag1 dadsbox.homegroup tag2 UDP: [192.168.0.2]:60925 tag3 DISMAN-EVENT-MIB::sysUpTimeInstance = 74695283 ==spacer==, SNMPv2-MIB::snmpTrapOID.0 = ExacqSCAN-MIB::exacqnotiftrap ==spacer==, ExacqSCAN-MIB::scanLastData.1 = "abc=def" ==spacer==

And here is the text from /tmp/mytstfile after I invoke a trap with the C program as the command:

Code:

arg count is

arg is /home/jiml/scan_snmp/testscript

Note in the C code that there is a commented out while statement, which should have the effect of wandering off into random memory if I invoke it when the actual argument count is 0 or one. Well, when I invoke it, I do get the command name listed as the first argument and the subsequent "arguments" are clearly environment variables and associated values.

So, the problem here is quite obviously that I do not know where to pick up the argument list that is passed to a shell script when it is invoked.

Could anyone here tell me where that argument list is kept? Perhaps a code fragment that will pick it up?