Best way to remove file extension from a string?

Question

So, I'm using a script I've made to convert videos to the webm format. A certain program calls the script, sending %f which is the full, absolute file name of the video, like this:

converter.sh %f

where %f has two possible extensions, .avi or .mpg.

# /bin/bash
ffmpeg -i $1 `dirname $1``basename $1 avi`webm && rm $1

It currently works perfectly when $1 contains a .avi file, because basename removes the .avi extension. When $1 ends with .mpg instead, the result is .mpgwebm.

How can I modify that script to be able to receive those two possible different formats?

Resuming: If $1 is /somedir/video.avi, the script should do:

ffmpeg -i /somedir/video.avi /somedir/video.webm

And if $1 is /somedir/video.mpg, the script should do:

ffmpeg -i /somedir/video.mpg /somedir/video.webm

I know this might be fool for some people, but I'm kind of new with the bash.

Stéphane Gimenez · Accepted Answer · 2011-08-15T04:23:01.463

9

You can use substitution mechanisms provided by most shells:

B=$(basename "$1"); D=$(dirname "$1");
ffmpeg -i "$1" "$D/${B%.*}.webm" && rm "$1"

In fact, basename and dirname could also be emulated by substitutions.

Note: direct .* suffix removal is not correct on paths like this.dir/file.

edited Aug 15 '11 at 04:23

answered Aug 15 '11 at 03:57

Stéphane Gimenez

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1

I allowed myself to quote the variable and to replace backquotes by `$(…)` – Stéphane Gimenez Aug 15 '11 at 03:58
Yes, but the files would be named `*.avi.webm` or `*.mpg.webm` because `basename` doesn't remove the extension unless you specify it after. – Tomas Aug 15 '11 at 04:01
Sorry, my first answer was stupid! Edited and still need improvement. – Stéphane Gimenez Aug 15 '11 at 04:06
Thanks, it's much better now. I didn't know about those substitution mechanisms. I don't think there is a better way. Using `sed` is a headache. – Tomas Aug 15 '11 at 04:11
One question: Why should I use `"$1"` instead of just `$1`? – Tomas Aug 15 '11 at 04:19
2

@Tomas: Without quotes and in the case your filenames contain spaces, they would be split into several paths. – Stéphane Gimenez Aug 15 '11 at 04:27
2

Why use `dirname`, `basename` and not to use directly `ffmpeg -i "$1" "${1%.*}.webm" && rm "$1" – enzotib Aug 15 '11 at 08:17
Also, `D=$(dirname "$1")` will change all multispace sequences to a single space, without quotes around `$()`. – enzotib Aug 15 '11 at 08:29
@enzotib: The note is there to avoid precisely this question! And word spitting is meaningless for variable assignations. I wish I could downvote your comments :-) – Stéphane Gimenez Aug 15 '11 at 11:49
Ehm, sorry, you are perfectly right. – enzotib Aug 15 '11 at 12:22

Best way to remove file extension from a string?

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