[SOLVED] imagemagick with for loop on the commandline does not work like expected

markush · 05-26-2011, 03:29 PM

Hello,

I have images in jpg format

Code:

CIMG0100.jpg
...
...
CIMG0131.jpg

consecutively. I used imagemagick to convert the files to gif with the following command

Code:

for i in {100..131}; do convert CIMG0$i.jpg CIMG0$i.gif; done # works

This worked like expected, but when afterwards I wanted to scale the images

Code:

for i in {100..131}; do convert -scale 25% CIMG00$i.gif CIMG00$i_scaled.gif; done # works not

it seems the system is working for about half a minute, but I get no output. The single command

Code:

convert -scale 25% CIMG100.gif CIMG100_scaled.gif # works

works as expected and gives me a scaled image.

Can anybody explain this behaviour? What does the convert command do in the second case? is the for-loop wrong?

Markus

crts · 05-26-2011, 04:05 PM

Hi Markus,

this a problem with the expansion mechanism in bash. Try this:

Code:

for i in {100..131}; do convert -scale 25% CIMG00${i}.gif CIMG00${i}_scaled.gif; done

The first pair of braces is not needed but apparently bash tries to expand the variable
$i_scaled
in the second case.

markush · 05-26-2011, 04:24 PM

Quote:

Originally Posted by crts

... apparently bash tries to expand the variable $i_scaled in the second case.

thanks very much for the answer, now I've got it working.

Markus