prompt wars

[zben at umd5.UUCP]

I started by picking up and enhancing some aliases originally posted by
Chris Torek in article <5150 at mimsy.uucp>.  I wanted to have the name of
the current directory in the prompt, but some amount of its parentage.
This precluded use of the :t modifier.  Via a combination of aliases I
got what I wanted (see below) but it was taking over four SECONDS to do
a change directory.  This was considered annoying, so I replaced the mess
with a C program (at the end of this article).  The change directory time
is now one second or less.

WHAT I WANTED:

Current machine (no need for domains) and the last two directory names of
the full name of the current directory.  Here is an example:

umd5[3] ~ % cd /usr/spool/news/comp/unix/questions
umd5[4] ...unix/questions %

ALIAS, SHELL SCRIPT, AND AWK SOLUTION:

in ".cshrc":

   alias set_prompt 'set prompt="`hnm1`[\\!] `dirs|cdt2` % "'
   alias cd 'cd \!*; set_prompt'
   alias pushd 'pushd \!*; set_prompt'
   alias popd 'popd \!*; set_prompt'
   set_prompt

in "~/bin/hnm1":

   #! /bin/sh
   # output user-friendly head of host name

   hostname | awk -F. '{ print $1 }'

in "~/bin/cdt2":

   #! /bin/sh
   # output user-friendly tail of CD name

   awk '{print $1}' |
   awk -F/ '
   (NF>3)||(NF>2)&&(length($1)!=0) {printf "..."}
   (NF>1) {printf "%s/",$(NF-1)}
   {printf "%s\n",$NF}'

ALIAS AND C PROGRAM SOLUTION:

in ".cshrc":

   alias cd 'cd \!*; set prompt="`dirs|genpro`"'
   alias pushd 'pushd \!*; set prompt="`dirs|genpro`"'
   alias popd 'popd \!*; set prompt="`dirs|genpro`"'
   set prompt="`dirs|genpro`"

and the following C program in "~/bin/genpro":

/* Generate prompt string
 * Ben Cranston 3/14/87
 *
 * designed to be called as:
 *
 * alias cd 'cd \!*; set prompt="`dirs|genpro`"'
 *
 * builds and outputs string:  <hostname> [!] <workdir>
 *
 * where <hostname> is the name of the current host sans trailing domains
 *       <workdir>  is the current directory, with all but the last two
 *                  directory names replaced by ... for brevity.
 *
 * I had all this working with "awk" scripts, but it was taking over
 * four SECONDS to switch directories.  This was considered wasteful.
 *
 */

#define BUFFSIZE 512

#include <sys/param.h>     /* MAXHOSTNAMELEN */
#include <strings.h>       /* string funcs   */

main(argc,argv)
int argc;
char **argv;
{
    char hostname[MAXHOSTNAMELEN];
    char dirs[BUFFSIZE], buff[BUFFSIZE];
    char *cp;
    char *p1, *p2;

    gethostname(hostname,sizeof(hostname));
    if ( 0 != (cp=index(hostname,'.')) )
	*cp = 0;        /* truncate hostname at first period (if any) */

    gets(dirs);
    if ( 0 != (cp=index(dirs,' ')) )
	*cp = 0;        /* truncate dir string at first space (if any) */

/* search backwards for slash.  if found, temporarily make null and
 * search backwards for slash again.  if found again, replace string
 * to the left of the second slash with "..."
 *
 * the additional test of (p1!=dirs) is for a special case, a two-string
 * explicitly rooted.  that is, "cd /etc/ns" will display as /etc/ns
 * rather than ...etc/ns
 */

    buff[0] = 0;
    cp = dirs;

    if ( 0 != (p2 = rindex(dirs,'/')) ) {
	*p2 = 0;
	if ( (0 != (p1 = rindex(dirs,'/'))) && (p1 != dirs) ) {
	    strcpy(buff,"...");
	    cp = p1 + 1;
	}
	*p2 = '/';
    }

    strcat(buff,cp);

    printf("%s[!] %s %% ",hostname,buff);
}

Needless to say this technique provides a skeleton upon which a variety
of personal preferences can be hung.  Enjoy!
-- 
                    umd5.UUCP    <= {seismo!mimsy,ihnp4!rlgvax}!cvl!umd5!zben
Ben Cranston zben @ umd2.UMD.EDU    Kingdom of Merryland UniSys 1100/92
                    umd2.BITNET     "via HASP with RSCS"