Re: OT: what does this expression mean?

[Todd Zullinger]

Anthony Joseph Messina wrote:

On Monday, September 12, 2016 12:22:48 PM CDT Mike Wright wrote:

   for f in "$(ls *.mp4)"; do
     ffmpeg -i "$f" -c:a libmp3lame "${f%.mp4}.mp3";
   done

You shouldn't need ls...

Indeed.  Parsing ls is almost never a good idea.

for f in *.mp4; do
 ffmpeg -i "$f" -c:a libmp3lame "${f%.mp4}.mp3";
done

for f in *.mp4; do
 ffmpeg -i "$f" -c:a libmp3lame "${f/.mp4/.mp3}";
done



--
Todd
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In some cultures what I do would be considered normal.

While we're at it, I might suggest that "${f%.mp4}.mp3" isn't as clear as "${f/.mp4/.mp3}" for this particular for loop. The pattern substitution method ${parameter/pattern/string} will also look more familiar to anyone who has used s/pattern/subst/ in vim, perl, etc, which is a small bonus. (And yeah, if we were playing shell golf, it could be shortened to "${f/%4/3}" -- but that's certainly not as legible. Saving those few characters is likely not worth having to remember that /% means "match at the end of the parameter." Although, using the % to anchor the substitution would be the most prudent thing even when using the full extension, in case you had a file with .mp4 elsewhere in the name. ;)

signature.asc
Description: PGP signature

--
users mailing list
users@lists.fedoraproject.org
To unsubscribe or change subscription options:
https://lists.fedoraproject.org/admin/lists/users@lists.fedoraproject.org
Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct
Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
Have a question? Ask away: http://ask.fedoraproject.org