Path: utzoo!attcan!uunet!ogicse!mintaka!bloom-beacon!athena.mit.edu!bjaspan
From: bjaspan@athena.mit.edu (Barr3y Jaspan)
Newsgroups: comp.unix.shell
Subject: Re: Built-in String Processing?
Message-ID: <1990Oct28.215656.20224@athena.mit.edu>
Date: 28 Oct 90 21:56:56 GMT
References: <1990Oct27.215051.14085@midway.uchicago.edu>
Sender: daemon@athena.mit.edu (Mr Background)
Reply-To: bjaspan@athena.mit.edu (Barr3y Jaspan)
Organization: Massachusetts Institute of Technology
Lines: 116

In article <1990Oct27.215051.14085@midway.uchicago.edu>, phd_ivo@gsbacd.uchicago.edu writes:
|> *************
|> I am running a csh with enhancements on my NeXT and on an HP-9000/8xx.
|> I have a macro to define my prompt to be the current directory, i.e.
|> 
|> 	alias cd                'cd \!* && set prompt="\! ${cwd}> "'
|> 
|> Unfortunately, this gives me a rather long string...

I wrote a short little hack to deal with this about a year ago.  Basically, it
can do the following things:

1) Truncate the cwd to a specified number of directories.
2) Replace a specified directory prefix with a constant string.
3) Remove a specified number of characters from the remainder of the cwd
after replacing a prefix.

We use AFS extensively at Athena (which results in VERY long path names!) so
I can easily provide examples of all three of these "features":

cwd                                  my prompt is
===================================  ==================================

/mit/bjaspan                         ~bjaspan%
/afs/athena/user/b/bjaspan           ~bjaspan%
/afs/athena/astaff/FOO               astaff: FOO%
/afs/athena/astaff/kerberos/FOO      kerberos: FOO%
/one/two/three/four/five             .../two/three/four/five%

The aliases that do all this magic for me are as follows:

alias pcmd '/mit/bjaspan/${bindir}/prompt 4 $cwd $home 0 ~  \
   /afs/athena.mit.edu/user/b/bjaspan 0 ~ /afs/athena.mit.edu/user 3 ~ \
   /afs/athena/user 3 ~ /afs/sipb.mit.edu/project/sipbsrc 1 "sipbsrc: " \
   /afs/athena.mit.edu/astaff/project 1 "aproj: " \
   /afs/rel-eng.athena.mit.edu/project/release/current/source 1 "source: " \
   /source 1 "source: "'
alias cd_magic 'set noglob && set prompt = "<%m> `pcmd`% " && unset noglob'
alias cd 'cd \!* && cd_magic'
alias pushd 'pushd \!* && cd_magic'
alias popd 'popd \!* && cd_magic'

Note that I've just copied these from my .aliases file.  The program that
actually does the real work, called "prompt", is included below.  It is
a bare-bones program (compiles to 3K on a VAX) that does NO ERROR CHECKING.
This qualifies as a gross hack of the first order, which means I don't care
if it dumps core on you because it works for me.  :-)  Your mileage
may vary.  Feel free to send me bugs, though.

Barr3y Jaspan, bjaspan@athena.mit.edu

PS:  I don't read this newgroup regularly (someone forwarded your question to
me because he knew I had written a prompt hack) so send replies personally.

--- snip snip ---

#define MHT	10
#define USAGE	"Usage: prompt max_dirs cwd [ hometop offset text ... ]\n"

int left_bcopy(src, dest, len)
   char	*src, *dest;
   int	len;
{
     while (len--)
	  *dest++ = *src++;
}

main(argc, argv)
   int	argc;
   char	**argv;
{
     char	*cwd, *hometop[MHT], *hometop_text[MHT];
     int	cwd_len, hometop_len[MHT], hometop_offset[MHT];
     int	hometop_num, i, max_dirs, count;

     if (argc < 3) {
	  write(1, USAGE, strlen(USAGE));
	  exit(1);
     }

     hometop_num = i = 0;
     max_dirs = atoi(*++argv);
     cwd = *++argv;
     cwd_len = strlen(cwd);

     while ((hometop_num < MHT) && (hometop[hometop_num] = *++argv)) {
	  hometop_offset[hometop_num] = atoi(*++argv);
	  hometop_text[hometop_num] = *++argv;
	  hometop_len[hometop_num] = strlen(hometop[hometop_num]);
	  ++hometop_num;
     }

     while (i < hometop_num) {
	  if (strncmp(hometop[i], cwd, hometop_len[i])==0 &&
	      (cwd_len >= hometop_len[i]+hometop_offset[i])) {
	       left_bcopy(cwd+hometop_len[i]+hometop_offset[i], cwd,
			  cwd_len-hometop_len[i]);
	       cwd[cwd_len-hometop_len[i]] = '\0';
	       cwd_len = strlen(cwd);
	       write(1, hometop_text[i], strlen(hometop_text[i]));
	       break; }
	  ++i;
     }

     if (max_dirs) {
	  for (i=cwd_len, count=0; i>0; i--) {
	       if (*(cwd+i) == '/' && (++count == max_dirs)) {
		    write(1, "...", 3);
		    write(1, cwd+i, cwd_len-i);
		    return 0; }
	  }
     }

     write(1, cwd, cwd_len);
     return 0;
}