Finding a file type assuming wrong extension

Question

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 free online tool [Falstaff](http://ec2-54-148-254-76.us-west-2.compute.amazonaws.com/falstaff/ "Falstaff") — Shaul Zevin, May 01 '15 at 13:22

jimmij · Accepted Answer · 2019-02-26T22:57:13.833

17

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.

edited Feb 26 '19 at 22:57

answered Oct 28 '14 at 02:39

jimmij

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Exactly what I was looking for. Thank you! – Aescula Oct 28 '14 at 03:03
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When using `file` be aware that it can give differing output across the various Unixes. http://unix.stackexchange.com/questions/151008/linux-file-command-classifying-files/ – slm Oct 28 '14 at 03:17
On Ubuntu I get the error message: `-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` – Avatar Sep 27 '22 at 06:10
Tipp: Use `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. – Avatar Sep 27 '22 at 06:15

score 5 · Answer 2 · edited Apr 16 '19 at 17:59

5

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

edited Apr 16 '19 at 17:59

Rui F Ribeiro

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answered Oct 28 '14 at 02:40

vfbsilva

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Finding a file type assuming wrong extension

2 Answers2