Out file extension linux

How to Determine the File Type of a File Using Linux

Find the file type of any file or group of files with the ‘file’ command

Most people look at the extension of a file and then guess the type of file from that extension. For example, when you see a file with an extension of gif, jpg, bmp, or png you think of an image file, and when you see a file with an extension of zip, you assume the file has been compressed using a zip compression utility.

A file can use one extension but be something altogether different. Linux doesn’t use file extensions; rather, the file’s type is part of the file name. To find out the true file type use the file command.

How the ‘file’ Command Works

The file command runs three sets of tests against a file:

• Filesystem tests
• Magic tests
• Language tests

The first set of tests to return a valid response prompts the file type to be printed.

Filesystem tests examine the return from a stat system call. The program checks to see if the file is empty and whether it is a special file. If the file type is found in the system header file, it is returned as the valid file type.

The magic tests check the contents of a file and specifically a few bytes at the beginning that help to determine the file type. Various files are used to help match up a file with its file type, and these are stored in:

• /etc/magic
• /usr/share/misc/magic.mgc
• /usr/share/misc/magic

Override these files by placing a file in your home folder called $HOME/.magic.mgc or $HOME/.magic.

The final tests are language tests. The file is checked to see if it is a text file. By testing the first few bytes of a file, the test deduces whether the file is an ASCII, UTF-8, UTF-16, or another format that identifies the file as a text file. When the character set is deduced, the file is tested against different languages.

How to Use the ‘file’ Command

The file command takes the following form:

The output will be something like this:

• /etc/passwd: ASCII text
• /etc/pam.conf: ASCII text
• /etc/opt: directory

Standard wildcards work, too. For example, to test all files in the present working directory, use:

To test for directories that start with the letter D (case sensitive) try this:

The results could be Desktop, Documents, and Downloads, for example.

Compressed Files

When you run the file command against a compressed file you see output something like this:

• file.zip: ZIP archive data, at least V2.0 to extract

While this result tells you that the file is an archive file, you don’t know the contents of the file. Look inside the zip file to see the file types of the files within the compressed file. The following command runs the file command against the files inside a ZIP file:

file -z filename

The output now shows the file types of files in the archive.

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Recursively look for files with a specific extension

I’m trying to find all files with a specific extension in a directory and its subdirectories with my bash (Latest Ubuntu LTS Release).

This is what’s written in a script file:

Unfortunately, when I start this script in terminal, it says:

(with $extension instead of ‘in’ )

What’s going on here, where’s the error? But this curly brace

10 Answers 10

is a bit shorter than that whole thing (and safer — deals with whitespace in filenames and directory names).

Your script is probably failing for entries that don’t have a . in their name, making $extension empty.

Example: To find all csv files in the current directory and its sub-directories, use:

The syntax I use is a bit different than what @Matt suggested:

(it’s one less keystroke).

Without using find :

1. There’s a < missing after browsefolders ()
2. All $in should be $suffix
3. The line with cut gets you only the middle part of front.middle.extension . You should read up your shell manual on $ and friends.

I assume you do this as an exercise in shell scripting, otherwise the find solution already proposed is the way to go.

To check for proper shell syntax, without running a script, use sh -n scriptname .

Though using find command can be useful here, the shell itself provides options to achieve this requirement without any third party tools. The bash shell provides an extended glob support option using which you can get the file names under recursive paths that match with the extensions you want.

The extended option is extglob which needs to be set using the shopt option as below. The options are enabled with the -s support and disabled with he -u flag. Additionally you could use couple of options more i.e. nullglob in which an unmatched glob is swept away entirely, replaced with a set of zero words. And globstar that allows to recurse through all the directories

Now all you need to do is form the glob expression to include the files of a certain extension which you can do as below. We use an array to populate the glob results because when quoted properly and expanded, the filenames with special characters would remain intact and not get broken due to word-splitting by the shell.

For example to list all the *.csv files in the recursive paths

The option ** is to recurse through the sub-folders and *.csv is glob expansion to include any file of the extensions mentioned. Now for printing the actual files, just do

Using an array and doing a proper quoted expansion is the right way when used in shell scripts, but for interactive use, you could simply use ls with the glob expression as

This could very well be expanded to match multiple files i.e. file ending with multiple extension (i.e. similar to adding multiple flags in find command). For example consider a case of needing to get all recursive image files i.e. of extensions *.gif , *.png and *.jpg , all you need to is

This could very well be expanded to have negate results also. With the same syntax, one could use the results of the glob to exclude files of certain type. Assume you want to exclude file names with the extensions above, you could do

The construct !() is a negate operation to not include any of the file extensions listed inside and | is an alternation operator just as used in the Extended Regular Expressions library to do an OR match of the globs.

Note that these extended glob support is not available in the POSIX bourne shell and its purely specific to recent versions of bash . So if your are considering portability of the scripts running across POSIX and bash shells, this option wouldn’t be right.

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How do I change the extension of multiple files?

I would like to change a file extension from *.txt to *.text . I tried using the basename command, but I’m having trouble on changing more than one file.

I’m getting this error:

14 Answers 14

*.txt is a globbing pattern, using * as a wildcard to match any string. *.txt matches all filenames ending with ‘.txt’.

— marks the end of the option list. This avoids issues with filenames starting with hyphens.

$ is a parameter expansion, replaced by the value of the f variable with .txt removed from the end.

Also see the entry on why you shouldn’t parse ls .

If you have to use basename , your syntax would be:

Here’s how I change all the file extensions in the current directory on Debian.

On MacOS, user Monkpit reports that they were able to use brew install rename to get this to work.

A simple command, the rename from util-linux , will do that for you, it replace every occurences of «txt» to «text» in all file matching «*.txt»:

Above works fine but limited to current directory. Try the command below, which is flexible with sub-directories. It will rename all .txt files under directory structure with a new extension.

The answers here referencing s/oldExtension/newExtension/ are wrong. If you use s/txt/text/ , you would convert footxt.txt to footext.txt , which is not what you want. Even if you use s/.txt/.text/ , that would convert footxt.txt to fo.text.txt .

You have to use \. to match the period ( . will match any character). And the trailing $ to match the end of the line. Only this will properly match the extension.

Reason #53 to switch to zsh:

Based on the @Prince John Wesley answer, here is a simple bash script for changing all extensions of files in the current directory from ext1 to ext2 . Also outputs names of the files being renamed.

Example usage (assuming the name of the script is change-ext ):

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Extract file basename without path and extension in bash [duplicate]

Given file names like these:

Why this doesn’t work?

What’s the right way to do it?

9 Answers 9

You don’t have to call the external basename command. Instead, you could use the following commands:

Note that this solution should work in all recent (post 2004) POSIX compliant shells, (e.g. bash , dash , ksh , etc.).

The basename command has two different invocations; in one, you specify just the path, in which case it gives you the last component, while in the other you also give a suffix that it will remove. So, you can simplify your example code by using the second invocation of basename. Also, be careful to correctly quote things:

A combination of basename and cut works fine, even in case of double ending like .tar.gz :

Would be interesting if this solution needs less arithmetic power than Bash Parameter Expansion.

Here are oneliners:

I needed this, the same as asked by bongbang and w4etwetewtwet.

Pure bash , no basename , no variable juggling. Set a string and echo :

Note: the bash extglob option must be «on», (Ubuntu sets extglob «on» by default), if it’s not, do:

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How do I change extension of multiple files recursively from the command line?

I have many files with .abc extension and want to change them to .edefg
How to do this from command line ?

I have a root folder with many sub-folders, so the solution should work recursively.

9 Answers 9

A portable way (which will work on any POSIX compliant system):

In bash4, you can use globstar to get recursive globs (**):

The (perl) rename command in Ubuntu can rename files using perl regular expression syntax, which you can combine with globstar or find :

70k files file structure. at least on my shell it most definitely did not replace it.

This will do the required task if all the files are in the same folder

To rename the files recursively use this:

One problem with recursive renames is that whatever method you use to locate the files, it passes the whole path to rename , not just the file name. That makes it hard to do complex renames in nested folders.

I use find ‘s -execdir action to solve this problem. If you use -execdir instead of -exec , the specified command is run from the subdirectory containing the matched file. So, instead of passing the whole path to rename , it only passes ./filename . That makes it much easier to write the regex.

• -type f means only look for files, not directories
• -name ‘*.abc’ means only match filenames that end in .abc
• ‘<>‘ is the placeholder that marks the place where -execdir will insert the found path. The single-quotes are required, to allow it to handle file names with spaces and shell characters.
• The backslashes after -type and -name are the bash line-continuation character. I use them to make this example more readable, but they are not needed if you put your command all on one line.
• However, the backslash at the end of the -execdir line is required. It is there to escape the semicolon, which terminates the command run by -execdir . Fun!

Explanation of the regex:

• s/ start of the regex
• \.\/ match the leading ./ that -execdir passes in. Use \ to escape the . and / metacharacters (note: this part vary depending on your version of find . See comment from user @apollo)
• (.+) match the filename. The parentheses capture the match for later use
• \.abc escape the dot, match the abc

$ anchor the match at the end of the string

/ marks the end of the «match» part of the regex, and the start of the «replace» part

version1_ add this text to every file name

$1 references the existing filename, because we captured it with parentheses. If you use multiple sets of parentheses in the «match» part, you can refer to them here using $2, $3, etc.

.abc the new file name will end in .abc. No need to escape the dot metacharacter here in the «replace» section

/ end of the regex

Hint: rename ‘s -n option is useful. It does a dry run and shows you what names it will change, but does not make any changes.

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