Bash while loop stops for no reason? [duplicate]

Question

I run the following bash script to rotate my mobile phone vids

while read filename ; do
    nf=$(echo $filename |rev | cut -f1 -d '/'|cut -f2- -d '.' |rev)
    echo $nf
    rm -f ffmpeg2pass-0.log
    rm -f rotate/tmp.avi
    ffmpeg -i $filename -c:v libxvid -pass 1 -c:a libmp3lame -qscale:a 4 -vf "transpose=2,transpose=2" "rotate/tmp.avi"
    ffmpeg -i $filename -c:v libxvid -pass 2 -c:a libmp3lame -qscale:a 4 -vf "transpose=2,transpose=2" "rotate/$nf.avi"
done <rotatelist_2

I know there are better ways to do this; I budged this together but I'm figuring out how to do the videos right so the rest don't need to look nice ;-))

However after the first run, the loop unexpectedly ends with no error message. I run similar loops for other things which work pretty well.

The echo is not called again so I guess there's something wrong with the loop itself. The linebreak in the list is a 0x0A, so it should be ok.

Does any of the commands within the loop read standard input too? If so, it ate the rest of rotatelist_2. It looks like it would have to be ffmpeg that does that, so I don't rate it highly as a possibility. You could use while read -u 3 filename; do ...; done 3<rotatelist_2 and see if that solves the problem. — Jonathan Leffler
– Jonathan Leffler, Commented Jan 26, 2015 at 21:59
That ugly second line can be replaced using basename. This assumes the filename extension is always the same, if it isn't, something like ${x%.*} will do (details under Remove matching suffix pattern. in the bash man page) — Marian
– Marian, Commented Jan 26, 2015 at 22:11
While we're kibitzing -- lots of bugs here that would be fixed by adding more quotes. "$filename" will deal with spaces, glob characters, etc. within names correctly; bare $filename won't. shellcheck.net will do the work of finding bugs of this variety for you. — Charles Duffy
– Charles Duffy, Commented Jan 26, 2015 at 22:18

Cyrus · Accepted Answer · 2015-01-26 22:04:27Z

2

Use

</dev/null ffmpeg ...
</dev/null ffmpeg ...

or

ffmpeg ... </dev/null
ffmpeg ... </dev/null

to prevent ffmpeg reading from rotatelist_2 via stdin.

answered Jan 26, 2015 at 22:04

Cyrus

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3 Comments

Charles Duffy Over a year ago

The other approach is to redirect from the file (and then read) on a FD other than stdin.

Cyrus Over a year ago

Yes, Jonathan Leffler's solution is smarter.

Cyrus Over a year ago

That's even better.

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