Extract filename and extension in Bash

First, get file name without the path:

filename=$(basename -- "$fullfile")
extension="${filename##*.}"
filename="${filename%.*}"

Alternatively, you can focus on the last '/' of the path instead of the '.' which should work even if you have unpredictable file extensions:

filename="${fullfile##*/}"

You may want to check the documentation :

• On the web at section "3.5.3 Shell Parameter Expansion"
• In the bash manpage at section called "Parameter Expansion"

~% FILE="example.tar.gz"

~% echo "${FILE%%.*}"
example

~% echo "${FILE%.*}"
example.tar

~% echo "${FILE#*.}"
tar.gz

~% echo "${FILE##*.}"
gz

For more details, see shell parameter expansion in the Bash manual.

pax> echo a.b.js | sed 's/\.[^.]*$//'
a.b
pax> echo a.b.js | sed 's/^.*\.//'
js

works fine, so you can just use:

pax> FILE=a.b.js
pax> NAME=$(echo "$FILE" | sed 's/\.[^.]*$//')
pax> EXTENSION=$(echo "$FILE" | sed 's/^.*\.//')
pax> echo $NAME
a.b
pax> echo $EXTENSION
js

The commands, by the way, work as follows.

The command for NAME substitutes a "." character followed by any number of non-"." characters up to the end of the line, with nothing (i.e., it removes everything from the final "." to the end of the line, inclusive). This is basically a non-greedy substitution using regex trickery.

The command for EXTENSION substitutes a any number of characters followed by a "." character at the start of the line, with nothing (i.e., it removes everything from the start of the line to the final dot, inclusive). This is a greedy substitution which is the default action.

This is the only one that worked for me:

path='folder/other_folder/file.js'

base=${path##*/}
echo ${base%.*}

>> file

This can also be used in string interpolation as well, but unfortunately you have to set base beforehand.

^{No previous answer used a bash regex}
Here's a pure bash solution that splits a path into:

• The directory path, with its trailing / when present
  ^{The regex that discards the trailing / is so much longer that I didn't post it}
• The filename, excluding the (last) dot extension
• The (last) dot extension, with its leading .

_{The code is meant to handle every possible case, you're welcome to try it.}

#!/bin/bash

for path; do

####### the relevant part ######

[[ $path =~ ^(\.{1,2}|.*/\.{0,2})$|^(.*/)([^/]+)(\.[^/]*)$|^(.*/)(.+)$|^(.+)(\..*)$|^(.+)$ ]]

dirpath=${BASH_REMATCH[1]}${BASH_REMATCH[2]}${BASH_REMATCH[5]}
filename=${BASH_REMATCH[3]}${BASH_REMATCH[6]}${BASH_REMATCH[7]}${BASH_REMATCH[9]}
filext=${BASH_REMATCH[4]}${BASH_REMATCH[8]}

# dirpath should be non-null
[[ $dirpath ]] || dirpath='.'

################################

printf '%s=%q\n' \
    path     "$path" \
    dirpath  "$dirpath" \
    filename "$filename" \
    filext   "$filext"

done

How does it work?

Basically, it ensures that only one sub-expression (delimited with | in the regex) is able to capture the input. Thanks to that, you can concatenate all the capture groups of the same type (for example, the ones related to the directory path) stored in BASH_REMATCH, because at most one will be non-null.

Here are the results of an extended but not exhaustive set of examples:

+--------------------------------------------------------+
| input             dirpath        filename       filext |
+--------------------------------------------------------+
''                  .              ''             ''
.                   .              ''             ''
..                  ..             ''             ''
...                 .              ..             .
.file               .              .file          ''
.file.              .              .file          .
.file..             .              .file.         .
.file.Z             .              .file          .Z
.file.sh.Z          .              .file.sh       .Z
file                .              file           ''
file.               .              file           .
file..              .              file.          .
file.Z              .              file           .Z
file.sh.Z           .              file.sh        .Z
dir/                dir/           ''             ''
dir/.               dir/.          ''             ''
dir/...             dir/           ..             .
dir/.file           dir/           .file          ''
dir/.file.          dir/           .file          .
dir/.file..         dir/           .file.         .
dir/.file.Z         dir/           .file          .Z
dir/.file.x.Z       dir/           .file.x        .Z
dir/file            dir/           file           ''
dir/file.           dir/           file           .
dir/file..          dir/           file.          .
dir/file.Z          dir/           file           .Z
dir/file.x.Z        dir/           file.x         .Z
dir./.              dir./.         ''             ''
dir./...            dir./          ..             .
dir./.file          dir./          .file          ''
dir./.file.         dir./          .file          .
dir./.file..        dir./          .file.         .
dir./.file.Z        dir./          .file          .Z
dir./.file.sh.Z     dir./          .file.sh       .Z
dir./file           dir./          file           ''
dir./file.          dir./          file           .
dir./file..         dir./          file.          .
dir./file.Z         dir./          file           .Z
dir./file.x.Z       dir./          file.x         .Z
dir//               dir//          ''             ''
dir//.              dir//.         ''             ''
dir//...            dir//          ..             .
dir//.file          dir//          .file          ''
dir//.file.         dir//          .file          .
dir//.file..        dir//          .file.         .
dir//.file.Z        dir//          .file          .Z
dir//.file.x.Z      dir//          .file.x        .Z
dir//file           dir//          file           ''
dir//file.          dir//          file           .
dir//file..         dir//          file.          .
dir//file.Z         dir//          file           .Z
dir//file.x.Z       dir//          file.x         .Z
dir.//.             dir.//.        ''             ''
dir.//...           dir.//         ..             .
dir.//.file         dir.//         .file          ''
dir.//.file.        dir.//         .file          .
dir.//.file..       dir.//         .file.         .
dir.//.file.Z       dir.//         .file          .Z
dir.//.file.x.Z     dir.//         .file.x        .Z
dir.//file          dir.//         file           ''
dir.//file.         dir.//         file           .
dir.//file..        dir.//         file.          .
dir.//file.Z        dir.//         file           .Z
dir.//file.x.Z      dir.//         file.x         .Z
/                   /              ''             ''
/.                  /.             ''             ''
/..                 /..            ''             ''
/...                /              ..             .
/.file              /              .file          ''
/.file.             /              .file          .
/.file..            /              .file.         .
/.file.Z            /              .file          .Z
/.file.sh.Z         /              .file.sh       .Z
/file               /              file           ''
/file.              /              file           .
/file..             /              file.          .
/file.Z             /              file           .Z
/file.sh.Z          /              file.sh        .Z
/dir/               /dir/          ''             ''
/dir/.              /dir/.         ''             ''
/dir/...            /dir/          ..             .
/dir/.file          /dir/          .file          ''
/dir/.file.         /dir/          .file          .
/dir/.file..        /dir/          .file.         .
/dir/.file.Z        /dir/          .file          .Z
/dir/.file.x.Z      /dir/          .file.x        .Z
/dir/file           /dir/          file           ''
/dir/file.          /dir/          file           .
/dir/file..         /dir/          file.          .
/dir/file.Z         /dir/          file           .Z
/dir/file.x.Z       /dir/          file.x         .Z
/dir./.             /dir./.        ''             ''
/dir./...           /dir./         ..             .
/dir./.file         /dir./         .file          ''
/dir./.file.        /dir./         .file          .
/dir./.file..       /dir./         .file.         .
/dir./.file.Z       /dir./         .file          .Z
/dir./.file.sh.Z    /dir./         .file.sh       .Z
/dir./file          /dir./         file           ''
/dir./file.         /dir./         file           .
/dir./file..        /dir./         file.          .
/dir./file.Z        /dir./         file           .Z
/dir./file.x.Z      /dir./         file.x         .Z
/dir//              /dir//         ''             ''
/dir//.             /dir//.        ''             ''
/dir//...           /dir//         ..             .
/dir//.file         /dir//         .file          ''
/dir//.file.        /dir//         .file          .
/dir//.file..       /dir//         .file.         .
/dir//.file.Z       /dir//         .file          .Z
/dir//.file.x.Z     /dir//         .file.x        .Z
/dir//file          /dir//         file           ''
/dir//file.         /dir//         file           .
/dir//file..        /dir//         file.          .
/dir//file.Z        /dir//         file           .Z
/dir//file.x.Z      /dir//         file.x         .Z
/dir.//.            /dir.//.       ''             ''
/dir.//...          /dir.//        ..             .
/dir.//.file        /dir.//        .file          ''
/dir.//.file.       /dir.//        .file          .
/dir.//.file..      /dir.//        .file.         .
/dir.//.file.Z      /dir.//        .file          .Z
/dir.//.file.x.Z    /dir.//        .file.x        .Z
/dir.//file         /dir.//        file           ''
/dir.//file.        /dir.//        file           .
/dir.//file..       /dir.//        file.          .
/dir.//file.Z       /dir.//        file           .Z
/dir.//file.x.Z     /dir.//        file.x         .Z
//                  //             ''             ''
//.                 //.            ''             ''
//..                //..           ''             ''
//...               //             ..             .
//.file             //             .file          ''
//.file.            //             .file          .
//.file..           //             .file.         .
//.file.Z           //             .file          .Z
//.file.sh.Z        //             .file.sh       .Z
//file              //             file           ''
//file.             //             file           .
//file..            //             file.          .
//file.Z            //             file           .Z
//file.sh.Z         //             file.sh        .Z
//dir/              //dir/         ''             ''
//dir/.             //dir/.        ''             ''
//dir/...           //dir/         ..             .
//dir/.file         //dir/         .file          ''
//dir/.file.        //dir/         .file          .
//dir/.file..       //dir/         .file.         .
//dir/.file.Z       //dir/         .file          .Z
//dir/.file.x.Z     //dir/         .file.x        .Z
//dir/file          //dir/         file           ''
//dir/file.         //dir/         file           .
//dir/file..        //dir/         file.          .
//dir/file.Z        //dir/         file           .Z
//dir/file.x.Z      //dir/         file.x         .Z
//dir./.            //dir./.       ''             ''
//dir./...          //dir./        ..             .
//dir./.file        //dir./        .file          ''
//dir./.file.       //dir./        .file          .
//dir./.file..      //dir./        .file.         .
//dir./.file.Z      //dir./        .file          .Z
//dir./.file.sh.Z   //dir./        .file.sh       .Z
//dir./file         //dir./        file           ''
//dir./file.        //dir./        file           .
//dir./file..       //dir./        file.          .
//dir./file.Z       //dir./        file           .Z
//dir./file.x.Z     //dir./        file.x         .Z
//dir//             //dir//        ''             ''
//dir//.            //dir//.       ''             ''
//dir//...          //dir//        ..             .
//dir//.file        //dir//        .file          ''
//dir//.file.       //dir//        .file          .
//dir//.file..      //dir//        .file.         .
//dir//.file.Z      //dir//        .file          .Z
//dir//.file.x.Z    //dir//        .file.x        .Z
//dir//file         //dir//        file           ''
//dir//file.        //dir//        file           .
//dir//file..       //dir//        file.          .
//dir//file.Z       //dir//        file           .Z
//dir//file.x.Z     //dir//        file.x         .Z
//dir.//.           //dir.//.      ''             ''
//dir.//...         //dir.//       ..             .
//dir.//.file       //dir.//       .file          ''
//dir.//.file.      //dir.//       .file          .
//dir.//.file..     //dir.//       .file.         .
//dir.//.file.Z     //dir.//       .file          .Z
//dir.//.file.x.Z   //dir.//       .file.x        .Z
//dir.//file        //dir.//       file           ''
//dir.//file.       //dir.//       file           .
//dir.//file..      //dir.//       file.          .
//dir.//file.Z      //dir.//       file           .Z
//dir.//file.x.Z    //dir.//       file.x         .Z

As you can see, the behaviour is different from basename and dirname. For example basename dir/ outputs dir while the regex will give you an empty filename for it. Same for . and .., those are considered directories, not filenames.

I timed it with 10000 paths of 256 characters and it took about 1 second, while the equivalent POSIX shell solution is 2x slower and solutions based on wild forking (external calls inside the for loop) are at least 60x slower.

remark: It's not necessary to test paths that contain \n or other notorious characters because all characters are handled the same way by the regex engine of bash. The only characters that would be able to break the current logic are / and ., intermixed or multiplied in a currently unexpected way. When I first posted my answer I found a few border cases that I had to fix; I can't say that the regex is 100% bullet proof but it should be quite robust now.

As an aside, here's the POSIX shell solution that yields the same output:

#!/bin/sh

for path; do

####### the relevant part ######

fullname=${path##*/}

case $fullname in
. | ..)
    dirpath="$path"
    filename=''
    filext=''
    ;;
*)
    dirpath=${path%"$fullname"}
    dirpath=${dirpath:-.}       # dirpath should be non-null
    filename=${fullname#.}
    filename="${fullname%"$filename"}${filename%.*}"
    filext=${fullname#"$filename"}
    ;;
esac

################################

printf '%s=%s\n' \
    path     "$path" \
    dirpath  "$dirpath" \
    filename "$filename" \
    filext   "$filext"

done

postscript: There are a few points for which some people might disagree with the results given by the above codes:

• The special case of dotfiles: The reason is that dotfiles are a UNIX concept.

• The special case of . and ..: IMHO it seems obvious to treat them as directories, but most libraries don't do that and force the user to post-process the result.

• No support for double-extensions: That's because you'd need a whole database for storing all the valid double-extensions, and above all, because file extensions don't mean anything in UNIX; for example you can call a tar archive my_tarred_files and that's completely fine, you'll be able to tar xf my_tarred_files without any problem.

IMHO the best solution has already been given (using shell parameter expansion) and are the best rated one at this time.

I however add this one which just use dumbs commands, which is not efficient and which noone serious should use ever :

FILENAME=$(echo $FILE | cut -d . -f 1-$(printf $FILE | tr . '\n' | wc -l))
EXTENSION=$(echo $FILE | tr . '\n' | tail -1)

Added just for fun :-)

Here is a sed solution that extracts path components in a variety of forms and can handle most edge cases:

## Enter the input path and field separator character, for example:
## (separatorChar must not be present in inputPath)

inputPath="/path/to/Foo.bar"
separatorChar=":"

## sed extracts the path components and assigns them to output variables

oldIFS="$IFS"
IFS="$separatorChar"
read dirPathWithSlash dirPath fileNameWithExt fileName fileExtWithDot fileExt <<<"$(sed -En '
s/^[[:space:]]+//
s/[[:space:]]+$//
t l1
:l1
s/^([^/]|$)//
t
s/[/]+$//
t l2
:l2
s/^$/filesystem\/\
filesystem/p
t
h
s/^(.*)([/])([^/]+)$/\1\2\
\1\
\3/p
g
t l3
:l3
s/^.*[/]([^/]+)([.])([a-zA-Z0-9]+)$/\1\
\2\3\
\3/p
t
s/^.*[/](.+)$/\1/p
' <<<"$inputPath" | tr "\n" "$separatorChar")"
IFS="$oldIFS"

## Results (all use separatorChar=":")

## inputPath        = /path/to/Foo.bar
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = Foo.bar
## fileName         = Foo
## fileExtWithDot   = .bar
## fileExt          = bar

## inputPath        = /path/to/Foobar
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = Foobar
## fileName         = Foobar
## fileExtWithDot   =
## fileExt          =

## inputPath        = /path/to/...bar
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = ...bar
## fileName         = ..
## fileExtWithDot   = .bar
## fileExt          = bar

## inputPath        = /path/to/..bar
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = ..bar
## fileName         = .
## fileExtWithDot   = .bar
## fileExt          = bar

## inputPath        = /path/to/.bar
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = .bar
## fileName         = .bar
## fileExtWithDot   = 
## fileExt          = 

## inputPath        = /path/to/...
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = ...
## fileName         = ...
## fileExtWithDot   =
## fileExt          =

## inputPath        = /path/to/Foo.
## dirPathWithSlash = /path/to/
## dirPath          = /path/to 
## fileNameWithExt  = Foo.
## fileName         = Foo.
## fileExtWithDot   =
## fileExt          =

## inputPath        = / (the root directory)
## dirPathWithSlash = filesystem/
## dirPath          = filesystem
## fileNameWithExt  =
## fileName         =
## fileExtWithDot   =
## fileExt          =

## inputPath        =  (invalid because empty)
## dirPathWithSlash =
## dirPath          =
## fileNameWithExt  =
## fileName         =
## fileExtWithDot   =
## fileExt          =

## inputPath        = Foo/bar (invalid because doesn't start with a forward slash)
## dirPathWithSlash =
## dirPath          =
## fileNameWithExt  =
## fileName         =
## fileExtWithDot   =
## fileExt          =

Here's how it works:

sed parses the input path and prints the following path components in order on separate lines:

• directory path with a trailing slash character
• directory path without a trailing slash character
• file name with extension
• file name without extension
• file extension with a leading dot character
• file extension without a leading dot character

tr converts the sed output into a separator character-delimited string of the above path components.

read uses the separator character as the field separator (IFS="$separatorChar") and assigns each of the path components to its respective variable.

Here's how the sed construct works:

• s/^[[:space:]]+// and s/[[:space:]]+$// strip any leading and/or trailing whitespace characters
• t l1 and :l1 refreshes the t function for the next s function
• s/^([^/]|$)// and t tests for an invalid input path (one that does not begin with a forward slash), in which case it leaves all output lines blank and quits the sed command
• s/[/]+$// strips any trailing slashes
• t l2 and :l2 refreshes the t function for the next s function
• s/^$/filesystem\/\\[newline]filesystem/p and t tests for the special case where the input path consists of the root directory /, in which case it prints filesystem/ and filesystem for the dirPathWithSlash and dirPath output lines, leaves all other output lines blank, and quits the sed command
• h saves the input path in the hold space
• s/^(.*)([/])([^/]+)$/\1\2\\[newline]\1\\[newline]\3/p prints the dirPathWithSlash, dirPath, and fileNameWithExt output lines
• g retrieves the input path from the hold space
• t l3 and :l3 refreshes the t function for the next s function
• s/^.*\[/]([^/]+)([.])([a-zA-Z0-9]+)$/\1\\[newline]\2\3\\[newline]\3/p and t prints the fileName, fileExtWithDot, and fileExt output lines for the case where a file extension exists, (assumed to consist of alphanumeric characters only), then quits the sed command
• s/^.*\[/](.+)$/\1/p prints the fileName but not the fileExtWithDot, and fileExt output lines for the case where a file extension does not exist, then quits the sed command.