Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!bria!mike
From: mike@bria.UUCP (mike.stefanik)
Newsgroups: comp.unix.questions
Subject: Re: Need help with subdirectories names
Message-ID: <245@bria.UUCP>
Date: 4 May 91 05:44:22 GMT
References: <12746@uhccux.uhcc.Hawaii.Edu>
Reply-To: uunet!bria!mike
Organization: MGI Group International, Los Angeles, CA
Lines: 94

In an article, denault@hale.ifa.hawaii.edu (Tony Denault) writes:
>I have an application where the user can type in a directory. I would like
>them to use short cuts names like ~username/whatever or $HOME/whatever. I
>suppose the program will need to read these and expand them somehow. How 
>they get expanded is where I get confused. 

Assume that in reference to $HOME, you are talking about expansion of
filenames like ~/this.file (the tilde alone specifies the $HOME path)

>For the ~username, I was thinking of reading the /etc/passwd file, search
>for the user name and determine their home directory.  
>
>Is my thinking correct or am I missing something? Can anyone provide some
>example code or routine that expands a relative or shortcut name into a full
>pathname.

Yes, your thinking is essentially correct.  Here is a short program that
does the tilde expansion.

WARNING: Flames regarding the bletcherous hack that follows will be promptly
         flushed down /dev/null (read: get a life and write some code of
	 your own, instead of reading mine! ;-)

--- snip snip snip ---------------------------------------------------------

#include <stdio.h>
#include <ctype.h>
#include <pwd.h>

char *explode();

main(argc,argv)
int argc;
char **argv;
{
	while ( --argc )
		puts(explode(*++argv));

	return 0;
}

char *explode(path)
char *path;
{
char *ptr, *getenv();
static char buf[256];
struct passwd *p, *getpwnam();

	strncpy(buf,path,256);

	if ( *path++ == '~' ) {
		if ( *path == '/' || *path == '\0' ) {
			if ( (ptr = getenv("HOME")) == NULL )
				return(buf);
			strcpy(buf,ptr);
			if ( strlen(path) > 0 ) {
				strcat(buf,"/");
				strcat(buf,++path);
				}
			return(buf);
			}

		ptr = path;
		while ( isalnum(*++path) )
			;

		if ( *path != 0 )
			*path++ = 0;

		if ( (p = getpwnam(ptr)) == NULL )
			return(buf);

		strcpy(buf,p->pw_dir);
		if ( strlen(path) > 0 ) {
			strcat(buf,"/");
			strcat(buf,path);
			}

		return(buf);
		}
	else
		return(buf);
}

----- snip snip snip -------------------------------------------------------

Well, that's it, in all of it's ugly glory.
Enjoy.

-- 
Michael Stefanik, MGI Inc, Los Angeles | Opinions stated are never realistic
Title of the week: Systems Engineer    | UUCP: ...!uunet!bria!mike
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If MS-DOS didn't exist, who would UNIX programmers have to make fun of?