bash, getting the mime type of a file handle
How would i get the mime type of a file-handle without saving it to disk? What i mean is a file that is not saved to disk, rather: i extracted it from an archive and plan on piping it to another script. Say i extracted the file like this:
tar -xOzf images.tar.gz images/logo.jpg | myscript Now inside myscript I would like to check the mime type of the file before further processing it. How would it go about this?
Read enough data off of the front of the pipeline input that you can test for it and then feed that data (and the rest of the piped data) into whatever processing step you perform next?
I don’ t know what you are trying to achieve. Perhaps on the fly file/mime type verification? This file -command could probably help: cat my_on_the_fly_file | file -b —mime-type — . It determines a file smime type «on the fly».
Marc, don’t be shy. Post this as the answer. tar -xOzf images.tar.gz images/logo.jpg | file — b — — mime type —
1 Answer 1
as some people think my comment above is helpful i post it as an answer. the file -command is able to determine a file’s mime type on the fly/when being piped. It ist able to read a file from stdin — printing the file’s —mime-type briefly/in a short manner when passing -b . Considering your example you probably want to extract a single file from an archive and dertermine its file/mime type.
$ tar -xOzf foo.tar.gz file_in_archive.txt | file -b --mime-type - text/plain so for a simple text file extracted from an archive to stdout it could look like the example above. hope that helped. regards
mimetype(1) — Linux man page
This script tries to determine the mime type of a file using the Shared MIME-info database. It is intended as a kind of file(1) work-alike, but uses mimetypes instead of descriptions.
If one symlinks the file command to mimetype it will behave a little more compatible, see «—file-compat». Commandline options to specify alternative magic files are not implemented the same because of the conflicting data formats. Also the wording of the descriptions will differ.
For naming switches I followed the manpage of file(1) version 4.02 when possible. They seem to differ completely from the spec in the ‘utilities’ chapter of IEEE Std 1003.1-2001 ( POSIX ).
Options
-a, —all Show output of all rules that match the file.
TODO: this method now just returns one match for each method (globs, magic, etc.). -b, —brief Do not prepend filenames to output lines (brief mode). —database=mimedir:mimedir. Force the program to look in these directories for the shared mime-info database. The directories specified by the basedir specification are ignored. -d, —describe Print file descriptions instead of mime types, this is the default when using «—file-compat». -D, —debug Print debug information about how the mimetype was determined. -f namefile, —namefile=namefile Read the names of the files to be examined from the file ‘namefile’ (one per line) before the argument list. —file-compat Make mimetype behave a little more file(1) compatible. This is turned on automaticly when you call mimetype by a link called ‘file’.
A single ‘-‘ won’t be considered a seperator between options and filenames anymore, but becomes identical to «—stdin». ( You can still use ‘—‘ as seperator, but that is not backward compatible with the original file command. ) Also the default becomes to print descriptions instead of mimetypes. -F string, —separator=string Use string as custom separator between the file name and its mimetype or description, defaults to ‘:’ . -h, —help -u, —usage Print a help message and exits. -i, —mimetype Use mime types, opposite to «—describe», this is the default when _not_ using «—file-compat». -L, —dereference Follow symbolic links. -l code, —language=code The language attribute specifies a two letter language code, this makes descriptions being outputted in the specified language. -M, —magic-only Do not check for extensions, globs or inode type, only look at the content of the file. This is particularly useful if for some reason you don’t trust the name or the extension a file has. -N, —noalign Do not align output fields. —output-format If you want an alternative output format, you can specify a format string containing the following escapes:
%f for the filename %d description %m mime type
Alignment is not available when using this, you need to post-process the output to do that. —stdin Determine type of content from STDIN , less powerfull then normal file checking because it only uses magic typing. This will happen also if the STDIN filehandle is a pipe.
To use this option IO::Scalar needs to be installed. -v, —version Print the version of the program and exit.
Environment
XDG_DATA_HOME XDG_DATA_DIRS These variables can list base directories to search for data files. The shared mime-info will be expected in the «mime» sub directory of one of these directories. If these are not set, there will be searched for the following directories:
$HOME/.local/share/mime /usr/local/share/mime /usr/share/mime
Files
The base dir for all data files is determined by two environment variables, see » ENVIRONMENT «. BASE/mime/packages/SOURCE.xml All other files are compiled from these source files. To re-compile them use update-mime-database(1). BASE/mime/globs Compiled information about globs. BASE/mime/magic Compiled information about magic numbers. BASE/mime/MEDIA/SUBTYPE.xml Descriptions of a mimetype in multiple languages, used for the «—describe» switch.
Diagnostics
If a file has an empty mimetype or an empty description, most probably the file doesn’t exist and the given name doesn’t match any globs. An empty description can also mean that there is no description available in the language you specified.
The program exits with a non-zero exit value if either the commandline arguments failed, a module it depends on wasn’t found or the shared mime-info database wasn’t accesable. See File::MimeInfo for more details.
Todo
The ‘—all’ switch doesn’t really show all matches, but only one per mime-typing method. This needs to be implemnted in the modules first.
Bugs
No known bugs, please mail the author if you find one.
mimetype doesn’t provide a switch for looking inside compressed files because it seems to me that this can only be done by un-compressing the file, something that defeats the purpose. On the other hand the option should exist for strict compatibility with file(1). Possibly a subclass should be made for this one day.
Author
Copyright
Copyright © 2003,2008 Jaap G Karssenberg. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY ; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE .