[solved] passing ImageMagick options in script : unrecognized command

Question

I'm working on a script that modifies a lot of images. I am trying to add the flexibility to pass in any valid IM argument and have it tacked on to a default resize operation.
I'm running into the problem where certain options give me the 'unrecoginized command' error even though they are valid.
I've included a test snippet. I'd be interested to see if my examples do/don't work for others.
#!/bin/bash
mogrify "${1}" -resize 800x900 "${2}"
#this won't work : bash ../IMargumenttest.sh '-modulate 150,50' img001.jpg
#and gives :mogrify: unrecognized option `-modulate 150,50' @ error/mogrify.c/MogrifyImageCommand/5147.
#this will work : bash ../IMargumenttest.sh '-contrast' img001.jpg
I've tried passing the arguments as single and double quoted options to no avail.
Thanks in advance.
Nick
Last edited by inkdinky (2012-02-29 22:30:22)

Answer 1

When you run the command "mogrify -modulate 150,50 ...", mogrify receives a list of arguments: "-modulate", followed by "-150,50", followed by whatever else you passed it. When it sees the "-modulate" argument, it knows that the next argument is a parameter for the modulate argument.
With your quoting it instead receives a single argument "-modulate 150,50". There is no option "-modulate 150,50", so it throws the unrecognized error.
There are a few ways to handle this, depending on what you need to do. If the order of the arguments doesn't matter, then you can do this:
mogrify -resize 800x900 "$@"
then run the script with "script -modulate 150,50 /path/to/image".  This works because "$@" is expanded by bash into separate words, so mogrify receives all of them as separate arguments.
If the resize command has to be right at the end, then you can do this:
img="$1"
shift
mogrify "$@" -resize 800x900 "$img"
In that case, you have to call the script with the file path as the first argument, followed by any other arguments to mogrify. It assigns the file path to the variable "img", then it shifts it off the array of input arguments.
You could also do it with array indexing, but I think this is simpler.
edit: Just in case you were wondering why "$@" is expanded and "$1" isn't, it's because "$@" is treated specially to enable this type of usage. "$*" also contains all of the input arguments, but it is not expanded into separate words when quoted.
Last edited by Xyne (2012-02-29 21:23:40)