ImageMagick convert on a multiple files

Solution 1:

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

Solution 2:

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

Parameter Expansion
...
  ${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).