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ksh - walking back up a directory PATH

 
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# 8  
Old 12-03-2008
actually it does sort of work but then goes into a loop, e.g:

$ ./test.ksh
before: Packages/Software/weblogic/9.2mp2/SunOS
after : Packages/Software/weblogic/9.2mp2
before: Packages/Software/weblogic/9.2mp2
after : Packages/Software/weblogic
before: Packages/Software/weblogic
after : Packages/Software
before: Packages/Software
after : Packages
before: Packages
after : Packages
before: Packages
after : Packages
before: Packages
after : Packages
before: Packages
after : Packages
.
.
.
ad infinitum...
# 9  
Old 12-03-2008
just realised why it didn't work, i was supplying the path without a preceeding / , e.g

var="Packages/Software/weblogic/9.2mp2/SunOS"

rather than

var="/Packages/Software/weblogic/9.2mp2/SunOS"

However i don't want to supply a preceeding / in the argument presented to the script, so i'll add that within the script.

Looks like this is the solution to go with. many thanks to everyone who contributed.

cheers

Steve
# 10  
Old 12-03-2008
Hi.

The string expression and utility dirname do essentially the same job, but with slightly different results for the end case. The expression will be faster, but for single-shot use, there is likely to be little contributing difference in time. Here are some some ways to deal with both:
Code:
#!/bin/ksh -

# @(#) s2       Demonstrate comparison of dirname and expression.

echo
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1)
set -o nounset

echo

var="/a/b/c/d/e/f"

echo " Expression of pathname at /:"
while [ -n "$var" ] ; do
     echo - "before: \"$var\""
     var="${var%/*}"
     echo - "after : \"$var\""
done

var="/a/b/c/d/e/f"
echo
echo " dirname of pathname at /:"
while [ "$var" != "/" ] ; do
     echo - "before: \"$var\""
     var="$(dirname $var)"
     echo - "after : \"$var\""
done

var="t/u/v/w/x/y/z"
echo
echo " Expression of pathname, NOT at /:"
while echo "$var" | grep '/' >/dev/null ; do
     echo - "before: \"$var\""
     var="${var%/*}"
     echo - "after : \"$var\""
done

var="t/u/v/w/x/y/z"
echo
echo " dirname of pathname, NOT at /:"
while [ "$var" != "." ] ; do
     echo - "before: \"$var\""
     var="$(dirname $var)"
     echo - "after : \"$var\""
done

exit 0

Producing:
Code:
$ ./s2

(Versions displayed with local utility "version")
SunOS 5.10
ksh M-11/16/88i

 Expression of pathname at /:
- before: "/a/b/c/d/e/f"
- after : "/a/b/c/d/e"
- before: "/a/b/c/d/e"
- after : "/a/b/c/d"
- before: "/a/b/c/d"
- after : "/a/b/c"
- before: "/a/b/c"
- after : "/a/b"
- before: "/a/b"
- after : "/a"
- before: "/a"
- after : ""

 dirname of pathname at /:
- before: "/a/b/c/d/e/f"
- after : "/a/b/c/d/e"
- before: "/a/b/c/d/e"
- after : "/a/b/c/d"
- before: "/a/b/c/d"
- after : "/a/b/c"
- before: "/a/b/c"
- after : "/a/b"
- before: "/a/b"
- after : "/a"
- before: "/a"
- after : "/"

 Expression of pathname, NOT at /:
- before: "t/u/v/w/x/y/z"
- after : "t/u/v/w/x/y"
- before: "t/u/v/w/x/y"
- after : "t/u/v/w/x"
- before: "t/u/v/w/x"
- after : "t/u/v/w"
- before: "t/u/v/w"
- after : "t/u/v"
- before: "t/u/v"
- after : "t/u"
- before: "t/u"
- after : "t"

 dirname of pathname, NOT at /:
- before: "t/u/v/w/x/y/z"
- after : "t/u/v/w/x/y"
- before: "t/u/v/w/x/y"
- after : "t/u/v/w/x"
- before: "t/u/v/w/x"
- after : "t/u/v/w"
- before: "t/u/v/w"
- after : "t/u/v"
- before: "t/u/v"
- after : "t/u"
- before: "t/u"
- after : "t"
- before: "t"
- after : "."

This worked on Linux and Solaris with ksh, pdksh, and bash. See man ksh and man dirname for details ... cheers, drl
# 11  
Old 12-03-2008
Quote:
Originally Posted by surfbus78
just realised why it didn't work, i was supplying the path without a preceeding / , e.g

var="Packages/Software/weblogic/9.2mp2/SunOS"
You could simply change the termination clause of the while loop then, yes? I just used "-n" (which means "nonzero", that is "empty" for strings) but you could use something else:

Code:
while [ "$oldvar" != "$var" ] ; do
     print - "before: $var"
     oldvar="$var"
     var="${var%/*}"
     print - "after: $var"
done

I would prefer using a solution which avoids external programs (like the grep in drls example) as long as this is possible because it slows down the execution of a shell script considerably. You might want to read this enightening thread for an in-depth discussion about the topic.

For the same reason (although this is only remotely connected with the threads theme), btw., i would suggest solely using "print" and not "echo" in a ksh script. "print" is a built-in command in ksh, while "echo" is not - in bash it is the other way round.

I hope this helps.

bakunin
Last edited by bakunin; 12-03-2008 at 11:39 AM..
# 12  
Old 12-03-2008
Hi.

I can't post in the other thread because it's locked, so I'll say a few words here.

There seems always to have been a tension, a trade-off between the choices for optimizing:

1) computer time

2) developer time

3) portability

The genius of Unix was to make it easy to port to different architectures, so that's generally where I start, and often with shell scripts, because they are so easily transportable. Scripting languages generally minimize developer time, an important measure for managers and organizations. As was mentioned in the other thread, if computer time really needs to be minimized, we'd move away from scripting. As we get better, accumulating experience and knowledge, as machines get faster, as software paradigms reveal more about the nature of problems and solutions, we can make choices that may harmonize all three characteristics ... cheers, drl
 
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