Generate and move thumbnails recursively

Question

I want a bash script which does the following:

Find pictures (jpg,jpeg,JPG,JPEG) recursively from current directory downwards
Generate a thumbnail with imagemagick's convert
Move thumbnail to other directory

My current script looks like this:

for f in `find . -type f -iname "*.jpg"`
  do
  convert ./"$f" -resize 800x800\> ./"${f%.jpg}_thumb.jpg"
  mv ./"${f%.jpg}_thumb.jpg" /home/user/thumbs/
done

It doesn't convert files (or folders with all content) which have spaces/special characters. I tried with print0 but it didn't help.

[Don't loop over `find`'s output](http://unix.stackexchange.com/q/321697) — don_crissti, Dec 26 '16 at 20:52

score 8 · Answer 1 · edited Dec 26 '16 at 23:27

Don't iterate over the output of find. The problem you are experiencing is a typical consequence of that.

Your example is a bit tricky due to the file renaming. One not very efficient but safe way to do it is with the -exec option of find, and an additional sh per each file, like this:

find . -type f -iname "*.jpg" -exec sh -c 'echo convert "$1" -resize 800x800\> /home/user/thumbs/"${1%.jpg}_thumb.jpg"' -- {} \;

If you didn't mind using the same name (with .jpg suffix instead of _thumb.jpg), then this simple form would work, and be much more efficient:

find . -type f -iname "*.jpg" -exec echo convert "{}" -resize 800x800\> /home/user/thumbs/"{}" \;

I added echo statements there to check the output before executing the commands. Remove them if the output looks good.

@janos, phk and don_crissti: I just accepted the answer from don, but I also upvoted the answers which are working. Thanks for your support guys, you had very interesting/educational answers to my first question on this site :) — LucaTony, Dec 27 '16 at 00:06

score 6 · Accepted Answer · answered Dec 26 '16 at 23:30

You could use more advanced options like -set combined with percent escapes (namely %t to extract the filename without directory or extension) to do the resize, rename and move of each file with a single convert invocation:

find . -type f -iname \*.jpg -exec convert {} -resize 800x800\> \
-set filename:name '%t' '/home/user/thumbs/%[filename:name]_thumb.jpg' \;

phk · Answer 3 · 2016-12-26T23:33:38.373

2

In your solution the file names got split on the default $IFS which includes spaces.

Try the following:

while IFS= read -rd '' f; do

    convert ./"$f" -resize 800x800\> ./"${f%.jpg}_thumb.jpg"
    mv ./"${f%.jpg}_thumb.jpg" /home/user/thumbs/

done < <(find . -type f -iname "*.jpg" -print0)

The find prints the file names separated by null bytes (\0) and using -d '' you set the delimiter of read to the same.

edited Dec 26 '16 at 23:33

answered Dec 26 '16 at 20:53

phk

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@don_crissti There is a second meaning to `-format` but I misunderstood it. There is also `-set` but I don't get its syntax: http://www.imagemagick.org/Usage/files/#save_escapes I don't think I will invest any more time into this. – phk Dec 26 '16 at 21:58
@don_crissti I would feed it all the files as parameters through `find […] -exec mogrify […] {} +` but apparently it's a bad idea for another reason: _"However all three images [in the example] are read into memory, and then modified by the one command. This is not a recommended solution for a number of large images, or very large numbers of images, due to the posibilty [sic] of reaching memory limits and thus going to disk swapping (thrashing)."_ (from the link posted in my previous comment). Maybe the possibility of such cases is also smth. worth mentioning in your long overview post. – phk Dec 26 '16 at 22:02
@phk Your snipped worked too, however I don't know which answer is the better/more efficient one. – LucaTony Dec 26 '16 at 22:51

Generate and move thumbnails recursively

3 Answers3