Mailinglist Archive: opensuse (1750 mails)

[David Bolt <bcrafhfr@xxxxxxxxxx>]

On Wed, 1 Oct 2008, drek wrote:-

> On 09/29/2008 04:02 PM, David Bolt wrote:
> > This should do:
> > WHICHEVER_VARIABLE_NAME_YOU_WANT=${PWD##*/}
> >                                   ^       ^
> > And these are curly braces.
> Thanks, but... Can you explain this? For me, it is just a magic guess
> with some #'s and a star and slash. How do you come up with this solution?

Randall has given you an explanation about what it does. As for where I
came across it, initially I saw some mention of it in a book[0] I have,
but didn't think much of it. Later I saw others suggesting similar
constructs as solutions, so looked at the bash man page and reread that
part of the book again. After doing so I've found that some of the
useful, but unused by me, parameter expansions can come in handy.

One of these useful expansions is this:

SOME_VAR=${SOME_VAR:-value}

which will assign the value "value" to SOME_VAR if it's empty, or leaves
it alone if it's not.

This would mean that you can get the exact same behaviour of basename by
using:

MY_DIR=${PWD##*/}
MY_DIR=${MY_DIR:-/}

or dirname using:

MY_DIR=${PWD%/*}
MY_DIR=${MY_DIR:-/}

Just to give you a bit more insight, here's a quick comparison:

davjam@adder:/local2/possible-viruses> MY_DIR="${PWD##*/}" ; 
MY_DIR="${MY_DIR:-/}" ; echo "${MY_DIR}" $(basename "${PWD}")
possible-viruses possible-viruses
davjam@adder:/local2/possible-viruses>
davjam@adder:/local2/possible-viruses> MY_DIR="${PWD%/*}" ; 
MY_DIR="${MY_DIR:-/}" ; echo "${MY_DIR}" $(dirname "${PWD}")
/local2 /local2
davjam@adder:/local2/possible-viruses>
davjam@adder:/local2/possible-viruses> pushd /
/ /local2/possible-viruses
davjam@adder:/local2/possible-viruses>
davjam@adder:/> MY_DIR="${PWD##*/}" ; MY_DIR="${MY_DIR:-/}" ; echo "${MY_DIR}" 
$(basename "${PWD}")
/ /
davjam@adder:/local2/possible-viruses>
davjam@adder:/> MY_DIR="${PWD%/*}" ; MY_DIR="${MY_DIR:-/}" ; echo "${MY_DIR}" 
$(dirname "${PWD}")
/ /


[0] Beginning Linux Programming, 3rd edition. ISBN 0-7645-4497-7

Regards,
        David Bolt

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