[SOLVED] Bash script

GPGAgent · 10-25-2020, 08:06 AM

Hi Folks, This is syntax problem not been able to ddg it so here goes:

Code:

X=$0        # save $0 in a local variable
Y=${0##*/}  # remove dir part
Z=${Y%.*}   # remove extension - if you want to do so
echo "X=\$0:$X  Y=\${0##*/} :$Y   Z=\${Y%.*}:$Z"

and you run it it gives this:

Code:

X=$0:./DVDOpts.sh  Y=${0##*/} :DVDOpts.sh   Z=${Y%.*}:DVDOpts
${0##*/}:DVDOpts.sh

How can I avoid using the intermediate variable Y?
I tried this:

Code:

echo "\${0##*/}:${0##*/} ${{0##*/}%.*} "

which gave the ereror message:

Code:

./DVDOpts.sh: line 21: \${0##*/}:${0##*/} ${{0##*/}%.*} : bad substitution

Turbocapitalist · 10-25-2020, 08:16 AM

How much of a requirement is Bash? It won't allow nesting but nested parameter expansion works fine in Zsh:

Code:

#!/bin/zsh

X=$0        # save $0 in a local variable
Y=${0##*/}  # remove dir part
Z=${Y%.*}   # remove extension - if you want to do so
echo "X=\$0:$X  Y=\${0##*/} :$Y   Z=\${Y%.*}:$Z"

echo "${${0##*/}%.*}"

GPGAgent · 10-25-2020, 08:26 AM

Cheers Turbo....

I don't know Zsh but by trial and error I found this:

Code:

echo $(basename ${0%.*})

which gives me just the script name - no path, no extension - perfect:

Code:

dev$ ./DVDOpts.sh -t T
DVDOpts

I'll mark this as solved in a while, just in case there's another way....

pan64 · 10-25-2020, 11:51 AM

basename will invoke an additional shell, and that will solve this issue. As it was mentioned you cannot nest (or embed) parameter expansion into each other (in bash). Using built-ins is much faster, and in your case that will be a two-step process.
From the other hand:

Code:

#instead of
echo $(basename ${0%.*})
# you can simply write:
basename ${0%.*}

(which will still use a new shell).

MadeInGermany · 10-25-2020, 01:31 PM

Yes,

Code:

bn=$(basename ${0%.*})

denotes a fork+exec (or even a fork+fork+exec).
While

Code:

x=${0%.*}; bn=${x##*/}

is plain inline.

ondoho · 10-25-2020, 02:47 PM

Once again I'm replying to one of your already SOLVED threads...

Quote:

Originally Posted by GPGAgent

How can I avoid using the intermediate variable Y?

Code:

X=${0##*/}  # save $0 in a local variable, remove dir part
X=${X%.*}   # remove extension - if you want to do so