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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!uw-beaver!ssc-vax!jeff
From: jeff@ssc-vax.UUCP (Jeffrey Jongeward)
Newsgroups: net.sources
Subject: Re: Son of 'which'
Message-ID: <157@ssc-vax.UUCP>
Date: Wed, 28-Aug-85 14:59:45 EDT
Article-I.D.: ssc-vax.157
Posted: Wed Aug 28 14:59:45 1985
Date-Received: Fri, 30-Aug-85 09:29:08 EDT
References: <225@tikal.UUCP>
Distribution: net
Organization: Boeing Aerospace Co., Seattle, WA
Lines: 75

> A week or so I posted a quick C version of the UCB shell script
> "which".  It takes as arguments command names and searches your path
> for instances of them.  The version I posted had some cute bugs: it
> didn't work if you didn't have a path or if there were a null
> component in the path (Thanks to Tom Truscott).  To the folks with v8
> shell: wish I had it, sounds like it make a lot of utilities, like
> this one, useless.
> 
> Here is a fancified version of the original one.
> 
> 	..!uw-beaver!teltone!larry
> 

Larry's "which" clone is a big win because it results in about a 3X
speed improvement over the sh-coded version.  However, in the 4.2BSD environment
(at least) there is 1 bug, and 3 incompatibilities with the standard
version.  In addition, the standard version embodies (at least one) bug of
it's own.

The Bugs:
Access(2) will return return 0 if a file is a directory and searchable,
but not executable (since X_OK only checks only the execute bit); so a
stat(2) is required in addition to check that the file is not a
directory.  In addition, access(... X_OK) is truly worthless
if the user is 'su' - since every existing file will return 0 
regardless of it's mode.

The 4.2BSD original embodies the 'su' problem as will; it will incorrectly
identify a non-executable in the search path.  The diffs posted below "fix"
that problem too - the price for this is to perform a somewhat pointless
access(2) call for the 'su'ed user, and to perform a worthless check
that some execute bit is set (since it duplicates the check in access)
for the non-su user.

The Incompatibilities:
1.  The program should bail out after the first found occurrence.
2.  The path should be printed delimited with ' ', not ':' when not found.
3.  the leading 'No' should be 'no' when not found.

Here are the diffs:

1a2,4
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/file.h>
4a8
> struct stat sb;
18a23
> 
39,41c44,49
< 	    if (access(buf, 1) == 0) {
< 		printf("%s\n", buf);
< 		found++;
---
> 	    if ( access(buf, 1) == 0 && !stat(buf,&sb) ) {
> 		if((sb.st_mode&S_IFDIR) == 0 && sb.st_mode&0111) {
> 			printf("%s\n", buf);
> 			found++;
> 			break;
> 		}
44,45c52,62
< 	if (!found) 
< 	    printf("No %s in %s\n", *av, origpath);
---
> 	if (!found)  {
> 	    char *optr = origpath;
> 	    char *oend = optr+strlen(origpath);
> 
> 	    while(optr < oend) {
> 		if(*optr == ':')
> 			*optr = ' ';
> 		optr++;
> 	    }
> 	    printf("no %s in %s\n", *av, origpath);
> 	}