How to Shorten the cwebp Command in Linux Mint with a Bash Function

I usually optimize images locally before uploading them to the live servers for my websites. Since I use Linux Mint, one of my regular tools for this job is cwebp, which I run directly from the command line to convert PNG and JPG images to WebP.

My most-used command is simple:

cwebp image-name.png -o image-name.webp

It works well, but after using it again and again, I started looking for a way to avoid typing the same filename twice every time I converted an image. When filenames are long, that small repetition becomes even more annoying.

Because I already use the Linux terminal for this task, I wanted a solution that would stay simple and keep using cwebp rather than adding another application. I solved it by creating a small Bash function called towebp.

Now, instead of writing the full command, I can simply run:

towebp image-name.png

and Bash automatically creates:

image-name.webp

This article explains the setup I use on Linux Mint, how the Bash function works, and how you can add the same shortcut to your own terminal.

Check That cwebp Is Installed

Before creating the shortcut, first confirm that cwebp is installed and available from your terminal.

Run:

which cwebp

On my Linux Mint system, the output is:

/usr/bin/cwebp

This confirms that the cwebp executable is installed and available in the shell path.

If the command returns nothing, install the WebP command-line utilities before continuing.

The Normal cwebp Command

The general cwebp command can include compression options and a quality value:

cwebp [options] -q quality input.png -o output.webp

For a basic conversion, I usually use:

cwebp image-name.png -o image-name.webp

The command is easy enough, but the filename has to be written twice.

For example, if the source image is:

php-allowed-memory-size-exhausted-real-fix.png

the full command becomes:

cwebp php-allowed-memory-size-exhausted-real-fix.png -o php-allowed-memory-size-exhausted-real-fix.webp

That is more typing than I want for a task I perform regularly.

Create a Short towebp Command with a Bash Function

Bash functions are a good fit for this because the shortcut needs to accept a filename, remove its current extension, and automatically create the WebP output filename.

Open your Bash configuration file:

nano ~/.bashrc

Go to the very bottom of the file and add:

# Convert image to WebP
towebp() {
  cwebp "$1" -o "${1%.*}.webp"
}

Then save the file in Nano:

• Press Ctrl + O
• Press Enter
• Press Ctrl + X

Reload the Bash Configuration

After changing ~/.bashrc, reload it with:

source ~/.bashrc

You can also close the terminal and open a new one. In my case, I reopened the terminal to make sure the updated Bash configuration was loaded cleanly.

That also resolved an initial towebp: command not found message I saw after adding the function.

Use the New towebp Command

Once the function is loaded, switch to any directory that contains the image you want to convert.

For example:

cd ~/Downloads/website-images

Then run:

towebp file-name.png

If the source file is:

file-name.png

the function creates:

file-name.webp

The original image remains unchanged.

How the Bash Function Works

The function contains this command:

cwebp "$1" -o "${1%.*}.webp"

There are two important parts to understand.

What “$1” Means

Inside a Bash function, $1 represents the first argument passed to the function.

If you run:

towebp photo.png

then:

$1 = photo.png

The quotes around "$1" matter because they allow filenames containing spaces to be handled correctly.

What “${1%.*}” Means

The expression:

${1%.*}

removes the shortest matching .* suffix from the filename. In this case, that effectively removes the existing file extension.

For example:

photo.png

becomes:

photo

The function then adds .webp, producing:

photo.webp

It Also Works with JPG and JPEG Files

The function is not limited to PNG files.

You can run:

towebp photo.jpg

and it creates:

photo.webp

The same approach works with JPEG files:

towebp photo.jpeg

which also creates:

photo.webp

Using Filenames with Spaces

The function can also handle filenames containing spaces, as long as you quote the filename when calling it.

For example:

towebp "My Website Image.png"

This creates:

My Website Image.webp

Add a Default WebP Quality Setting

If you normally use the same quality setting for most of your website images, you can include that value directly in the function.

For example, to always use quality 82:

# Convert image to WebP using quality 82
towebp() {
  cwebp -q 82 "$1" -o "${1%.*}.webp"
}

Now this:

towebp image.png

runs the equivalent of:

cwebp -q 82 image.png -o image.webp

This is useful if you want to keep a consistent WebP compression setting across images prepared for your websites.

Troubleshooting: towebp Command Not Found

If you run the shortcut and see:

towebp: command not found

first confirm that the function was actually saved in ~/.bashrc.

grep -n -A3 'towebp' ~/.bashrc

You should see something similar to:

120:towebp() {
121-  cwebp "$1" -o "${1%.*}.webp"
122-}

Next, check whether Bash has loaded the function:

type towebp

If it is loaded correctly, Bash should report:

towebp is a function

You can also check your ~/.bashrc file for Bash syntax errors:

bash -n ~/.bashrc

If there are no syntax errors, the command normally produces no output.

If the function is present in ~/.bashrc but still is not available, close the current terminal window and start a new one. That fixed the problem in my setup.

Why Use a Bash Function Instead of an Alias?

A Bash alias is useful when you want to replace one fixed command with another fixed command. This shortcut needs a little more logic because it has to accept an input filename and build a new output filename automatically.

A function handles that much more cleanly.

It lets this:

towebp image.png

automatically behave like:

cwebp image.png -o image.webp

without requiring you to write the output filename yourself.

Final Bash Function

If you only need the basic version, this is the complete function:

# Convert image to WebP
towebp() {
  cwebp "$1" -o "${1%.*}.webp"
}

Add it to:

~/.bashrc

Then reload Bash:

source ~/.bashrc

or close the terminal and open a new one.

After that, converting an image becomes:

towebp file-name.png

and the output file is created as:

file-name.webp

Conclusion

The standard cwebp command already does its job well, but if you use it frequently, repeating the same filename for input and output becomes unnecessary work.

A small Bash function solves that neatly. The towebp command keeps the original filename, removes the old extension, and creates a WebP file with the same base name.

For anyone who regularly prepares images locally before uploading them to WordPress or another website, this is a simple Linux Mint customization that makes the command-line workflow faster and easier to use.