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PHP Learner
Asked: 2015-02-18 04:18:21 +0800 CST

How to assign (set) a MIME type to a file?

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Is there any command that could set MIME type of a file? for example: 

mime --set --MIME="image/pjpeg" filename.jpg
command-line

2 Answers

  1. Question is already answered by @PHPLearner in a comment. However, here is a longer answer.

    There is no particular command like mime as asked in the question, and no doubt one such command can be created. For adding a new MIME type, all it takes is editing the /etc/mime.types file.

    Let's say you want to add MIME type with extension .btc, then

    1. Check If MIME type already exists

    Open a command line and enter the line below (replace btc with your extension)

    grep 'btc' /etc/mime.types

    Now, this command will output a line, If that MIME type is already added. It looks like this for particular MIME searches

    $ grep 'cpp' /etc/mime.types
text/x-c++src                        c++ cpp cxx cc

$ grep 'py' /etc/mime.types
application/x-python-code                       pyc pyo
text/vnd.debian.copyright
text/x-python                                   py 

$ grep 'btc' /etc/mime.types

    If your extension does not output any lines (as for btc in this case), or if the lines outputed do not include your extension, you must create a new MIME type. Otherwise your extension already has a MIME type included in the file /etc/mime.types.

    2.1 Creating the MIME type (IF needed)

    If there was no output, or the output given did not include your extension, we must add a MIME type. For that type at command line

    gksudo gedit /etc/mime.types

    Modify the following text so that the word "extension" is replaced with your file extension (no period mark), add the line to the end of the mime.types file, and save. Here our extension is bitcoin and we write btc (NOT .btc) that will be seen as an extension for the bitcoin files.

    text/extension                   extension

    And copy the modified 'text/extension' part.

    In our case it will look like

    text/bitcoin-text                btc

    Save the file and exit.

    2.2 Adding MIME type using .xml file and update-mime-database

    If editing /etc/mime.types file doesn't works for your extension, then you can try this workaround.

    Create a new .xml file that describes your extension like this & Save it.

    <?xml version="1.0" encoding="utf-8"?>
<mime-type xmlns="http://www.freedesktop.org/standards/shared-mime-info">
<mime-info type="text/bitcoin-text">
<glob pattern="*.btc"/>
</mime-info>
</mime-type>

    Now add this file into /usr/share/mime/packages folder (ref).After you've added or modified whatever you need, run the command

    sudo update-mime-database /usr/share/mime

    3. Adding an Icon to MIME type

    Now we need to associate an icon with the MIME type. Get an SVG icon and name it "text-extension.svg", or whatever your modified MIME type is named; this will be the icon to represent all instances of the MIME type on your system.

    So, We rename the .svg file so that the it matches bitcoin-text.svg (or "insertYourMIMEtype.svg") so that the slashes are replaced with "-" and there are no capital letters.

    Then simply run the following commands, with 'bitcoin-text' replaced with your MIME type.

     sudo cp bitcoin-text.svg /usr/share/icons/gnome/scalable/mimetypes
 sudo gtk-update-icon-cache /usr/share/icons/gnome/ -f

    Relogin and all files ending in the MIME extension will display with that icon.

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  2. To actually answer your question: MIME types aren't real. There isn't some piece of metadata in the file that says "this is a image/png". Instead, MIME types are guessed based on file extension and magic number. To serve a file as having a specific MIME type, you need to configure your web-server appropriately. See https://stackoverflow.com/questions/29017725/how-do-you-change-the-mime-type-of-a-file-from-the-terminal

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