I have 3 files in a directory:


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:


What I want is:


How do I do this?


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


$ 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
      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).

  • 1
    +1 because it follows the Unix philosophy that each tool should do small part of the work efficiently, rather than one tool does everything. Jul 27 at 11:51
  • 1
    I suggest changing the filenames from *.jpg to ./*.jpg in case some name begins with -.
    – 7efkvNEq
    Jul 27 at 15:13
  • @7efkvNEq, Thanks, that's a good idea.
    – sudodus
    Jul 27 at 15:21
mkdir small
for f in *.jpg ; do convert $f -resize 1200x900 small/$f ; done
  • 1
    This does not answer the question. The filenames are the same. Jul 26 at 19:10
  • @AlLelopath, True, the filenames are the same, but in another directory. I have used this method and I think it is good ;-)
    – sudodus
    Jul 26 at 20:07

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