Shell Programming and Scripting

All,
I know that this will remove a file extension from a file name, but reading on the documentation on how it works confuses me.

Code:

${filename%.*}

Can anyone explain what exactly is going on here? Filename is the pattern and % says to cut anything that starts with .?

Also, can I run this command and then insert a timestamp in between the filename and the extension? I am hoping to do something like mv $filename ${filename%.*}`date`.txt. Can this be done without a for loop for each file with the exec command?

Code:

find $DESTLOC -maxdepth 1 -type f -exec mv -f {} $ARCHLOC/

The keyword should be a shell's parameter expansion.

Code:

% cut out shortest suffix (right side)
%% cut out longest suffix (right side)
# cut out shortest prefix (left side)
## cut out shortest prefix (left side)

#### EXAMPLE (the slash is just the delimeter) ####

$> VAR=eins/zwei/drei/vier
$> echo ${VAR%/*}
eins/zwei/drei
$> echo ${VAR%%/*}
eins
$> echo ${VAR#*/}
zwei/drei/vier
$> echo ${VAR##*/}
vier

This book is a good choice regarding such things and many other helpful concepts etc.:
Pro Bash Programming: Scripting the Linux Shell - Links

Thanks, I guess "expansion" is what confused me as I don't equate expansion with removal. So really, you aren't expanding, but deleting.

You can delete the filename extensions easily by doing:

Code:

for i in *.txt; do mv $i ${i%%.*}; done

If you want to put some file extensions back to files, copy the files into their own directory (for precaution) and put file extensions on them like this (.txt in this case):

Code:

for i in *; do mv $i $i.txt; done

Thanks, I figured I could do it with the for loop I was just wondering if I could some how do it with the find -exec mv command