ImageMagick convert on a multiple files

I have 3 files in a directory:

aaa.jpg
bbb.jpg
ccc.jpg 

I can scale down an image using ImagkMagick convert:

convert aaa.jpg -resize 1200x900 aaa-small.jpg 

I want to do all the images in the directory, something like:

convert *.jpg -resize 1200x900 *-small.jpg 

but this results in files named like so:

*-small-0.jpg
*-small-1.jpg
*-small-2.jpg 

What I want is:

aaa-small.jpg
bbb-small.jpg
ccc-small.jpg 

How do I do this?

3 Answers

It's frustratingly opaque in the documentation, but you can pass a quoted shell glob to convert (quoted to prevent the shell from expanding it prematurely), and use Filename Percent Escapes to construct output filenames in the form %[filename:label] (where label is an arbitrary user-specified label), using the input basename escape %[basename] or its legacy equivalent %t:

$ ls ???.jpg
aaa.jpg bbb.jpg ccc.jpg

then

$ convert '*.jpg' -set filename:fn '%[basename]-small' -resize 1200x900 '%[filename:fn].jpg'

resulting in

$ ls ???-small.jpg
aaa-small.jpg bbb-small.jpg ccc-small.jpg

In a for loop it is possible to use the features described in man bash at

Parameter Expansion
... ${parameter%word} ${parameter%%word} Remove matching suffix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value of parameter, then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the ``%'' case) or the longest matching pattern (the ``%%'' case) deleted. If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list.

The following one-liner should do the job

for f in ./*.jpg ; do convert "$f" -resize 1200x900 "${f%.jpg}-small.jpg" ; done

This works in bash, which is the standard shell of Ubuntu. I think it is easier to remember than the elegant method by Steeldriver (who uses only convert and no for construct).

mkdir small
for f in *.jpg ; do convert $f -resize 1200x900 small/$f ; done