I have an image archive I keep up. Sometimes, the sites I pull them from reformat the file while keeping the extension the same, most often making PNG images into JPG's that are still named ".png". Is there a way to discover when this has happened and fix it automatically?
When on Windows, I used IrfanView for this, but that needs a Wine wrapper.
You can use file command:
$ file file.png
file.png: PNG image data, 734 x 73, 8-bit/color RGB, non-interlaced
$ mv file.png file.txt
$ file file.txt
file.txt: PNG image data, 734 x 73, 8-bit/color RGB, non-interlaced
The file does some tests on file to determine its type. Probably the most important test is comparing a magic number (string in a file header) with pre-defined list.
file be aware that it can give differing output across the various Unixes. unix.stackexchange.com/questions/151008/…
-bash: file: command not found. So we need to install the package first (I thought it comes with the default installation). You need to install "file" by sudo apt install file
file --mime-type if you only want the MIME type itself without encoding information, e.g. application/pdf. Pass the option -b if you don't want to display the file name at the beginning of the line.
You can try imagemagicks identify command: http://www.imagemagick.org/script/identify.php
Example:
$ identify rose.jpg
rose.jpg JPEG 640x480 sRGB 87kb 0.050u 0:01
