Mailinglist Archive: opensuse (686 mails)

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Re: [opensuse] bash: how to get file extension
Brian K. White said the following on 07/15/2013 12:00 PM:

% F=/path/to/foo.blah.txt
% echo "${F##*.}"
txt

and for that matter


$ F=/usr/bin/foo.x.y.z.txt
$ echo "${F##*.}"
txt



You are saying you want the final answer to _include_ the dot? That is
an unreasonably complicated thing to try to do for not enough gain. It's
possible with sed, but you're working too hard to figure out that
sed/regex syntax, and by forking a process to run sed, also making the
computer work too hard.

The simple and practical answer is just to add the dot back in yourself
like this:

ext=".${FILENAME##*.}"

LOL!


That is not technically truth right there. If the file has no extension
then you will get ext="." which basically claims that the original file
name ended with a dot, which is not true.

Ah,actually

$ F=/usr/bin/fooxyztxt
$ echo ."${F##*.}"
./usr/bin/fooxyztxt



But since you are probably just looking for a match from a list of known
extensions and they all have a leading dot, this should be fine.



Now the important part, sometimes known as
Context is Everything

How to code a particular thing vastly depends on the rest of the job it
is a part of. You can make your life unnecessarily hard by trying to get
a detail to work a certain way without considering the rest of the
context. In this case, I don't think your really need exactly what you
asked for and above is good enough, except for two more things:

1 - You probably want to convert ext to all upper or all lower so that
you find the matches that YOU and I know are correct even if the
computer doesn't. You know that file.Avi is an avi file even though it
doesn't match either .avi or .AVI.

For that you can typeset ext so it is all up or all low.
put this near the top of the script, before ext is ever used.
typeset -l ext
or
typeset -u ext


2 - You probably want to try using file magic (the "file" command) as a
fall-back in case $ext was not recognized. Or even other more
specialized utilities that use more in-depth knowledge of common media
files to identify files by their contents instead of relying on their
file names.

Take one of your video files and rename it without the extension.
now run
file "movie title here"

If you had trouble just clipping the ext off of a filename then parsing
this output in a script is probably right out, but the info is there.

Of course if you have a lot of such files to process then perhaps streaming though sed or awk would be simpler, but as Brian says, it depends on the alrger context.





--
How long did the whining go on when KDE2 went on KDE3?

The only universal constant is change. If a species can not adapt it
goes extinct. That's the law of the universe, adapt or die.
-- Billie Walsh, May 18 2013
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