Legacy ImageMagick Discussions Archive

Hello. I tried writing something similar to the following minimal testcase to test using identify if a file (if it exists) is a valid image or not, and if yes, to move it to a particular location:

Code: Select all

#! /bin/sh
ifile=input.jpg
identify $ifile &> /dev/null && {
        echo "DEBUG: moving the jpg"
        mv -v $ifile foo.jpg
} || {
        rm $ifile
        echo "Input file not a valid image"
}

However it is failing with the following session transcript illustrating the curious failure:

Code: Select all

$ ls
im-test.sh
$ ./im-test.sh 
DEBUG: moving the jpg
mv: cannot stat ‘input.jpg’: No such file or directory
rm: cannot remove ‘input.jpg’: No such file or directory
Input file not a valid image
$ identify.im6: unable to open image `input.jpg': No such file or directory @ error/blob.c/OpenBlob/2638.
^C
$
$ touch input.jpg
$ ./im-test.sh 
DEBUG: moving the jpg
‘input.jpg’ -> ‘foo.jpg’
$ identify.im6: unable to open image `input.jpg': No such file or directory @ error/blob.c/OpenBlob/2638.
^C
$
$ identify -version
Version: ImageMagick 6.7.7-10 2013-09-10 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2012 ImageMagick Studio LLC
Features: OpenMP

I totally do not understand how identify is apparently returning a success exit status so that the && part of the script is executing, but actually identify is apparently trying to examine the image *after* the && part has moved the image elsewhere!

This is mucking up the behaviour of my script. Please help!

I'm not a bash scripter, but your script looks strange to me. I assume "&&" has higher precedence than "||". "identify" returns 1 for failure or 0 for success. Your expression interpreter tries to make both sides of && true, ie 1. So the mv will be tried only if identify fails.

But I could be wrong about this.

Hi thanks for your reply snibgo.

I found out that the problem was that I was using sh and not bash in my script. sh (which is symlinked to dash on my Ubuntu system) does not recognize the &> operator to redirect both stderr and stdout. I figured this out at unix.stackexchange. If I change the script to use /bin/bash at the shebang line, all is fine.

Thanks anyhow for replying.

Legacy ImageMagick Discussions Archive

Trying to use identify to examine if an image is valid

Trying to use identify to examine if an image is valid

Re: Trying to use identify to examine if an image is valid

Re: Trying to use identify to examine if an image is valid