How to know your current shell from C code

[Jim Webb]

In article <josef.653134656 at peun11>, josef at nixpbe.UUCP (Moellers) writes:
> In <1990Sep11.164436.9592 at cadence.com> mikel at cadence.cadence.com writes:
> 
> 
> >        Recently I had a UNIX question.  I have a c program and
> >I want to know which shell(sh,csh,ksh) is my parent.  Is there
> >any way to do this?  Environment variable is not acceptable.
> 
> Quick'n'dirty:
>       ...
> 	ppid = getppid()
> 	ps = popen("ps", "r");

Since you know the parent's pid, why don't you pass it on the the
ps command?  Ergo:

	char psbuf[20];
	sprintf(psbuf,"/bin/ps -p%d",getppid());
	ps = popen(psbuf, "r");

> 	fgets(line, 80, ps);	/* skip "PID TTY TIME COMMAND" */
> 	shell = (char *) 0;

Doing this, you don't need to "grep" thru the output to find
the process as you do here:

> 	while (fgets(line, 80, ps) != NULL)
> 	{
> 		pspid = atoi(line);
> 		if (pspid == ppid)
> 		{
> 			shell = line+22;  <--------------------------+
> 			break;                                       |
> 		}                                                    |
> 	}                                                            |
                                                                     |
> 	shell[strlen(shell)-1] = '\0';                               |
                                                                     |
You really ought to do the above line AFTER making sure that some    |
was assigned to it :-)  Like right here instead ---------------------+
Granted, in this case all it would probably do is write a \0 into
line[79], but it still is a bad practice to get into, especially
since you test for errors later on here:

> 	if (shell == (char *) 0)
> 		printf("Huh??");
> 	else
> 		printf("Your friendly neighbourhood shell is \"%s\"\n", shell);

Another thing you might want to clobber out is the - at the begining of
login shells (eg -sh):

	if (*shell == '-') shell++;

ps
I just hope this isn't going into a set[u|g]id program, popen()'s are
quite scary in that case.....

-- 
Jim Webb                "Out of Phase -- Get Help"               att!mtune!jrw
                  "I'm bored with this....Let's Dance!"