We want to create a script (called zhead) that can be executed from any directory. To do this, we’ll first create a text file that contains the script, then add it to a directory included in the $PATH environment variable.

In this example, we’ll write a script that displays the first 10 lines of a gzipped file and call it zhead.

When we execute any command, we’re actually running a program — and a program is just a file. For instance, the ls command is usually located at /usr/bin/ls. So why can we use it from anywhere?

That’s because when we type a command, the shell searches for it in the directories listed in the $PATH environment variable. This variable is a colon-separated list of directories that the shell scans to locate executables. If it finds the command in one of those directories, it runs it; otherwise, it shows an error.

To see the content of your $PATH variable:

echo $PATH

You’ll see a list of directories separated by colons. These are the directories your shell searches for commands.

💡 To display them as a list, you can use sed to replace colons with newlines:

echo $PATH | sed 's/:/\n/g'

1. Create the script

Let’s create the script in your home directory:

nano ~/zhead

In the nano editor, add the following content:

#!/bin/bash

# Check if a filename was supplied
if [ $# -eq 0 ]; then
    echo "Error: No file supplied"
    echo "Usage: zhead <gzipped-file>"
    exit 1
fi

gzip -dc "$1" | head

• ⚠️ Shebang line (#!) — must be the first line of the script, with no spaces after #!. It tells the system which interpreter to use. Here, /bin/bash specifies Bash.
• The if statement checks whether an argument was provided; if not, it shows an error and exits.
• The gzip command decompresses the gzipped file and pipes the result to head, which displays the first 10 lines.

Press Ctrl+X, then Y, and Enter to save and exit.

📦 There is a more complete version of the script on github

2. Create the ~/bin directory

We’ll place the script in a personal bin directory inside your home folder - where you have write permissions. (Remember: ~ is shorthand for your home directory.)

If it doesn’t exist already, create it:

mkdir -p ~/bin

3. Move the script to ~/bin

Move the script into the bin directory:

mv ~/zhead ~/bin/

If you try to execute it now:

~/bin/zhead

You’ll likely get a “Permission denied” error because the file isn’t executable yet.

Check its permissions:

ls -l ~/bin/zhead

Example output:

-rw-r--r-- 1 ubuntu ubuntu 123 Oct 19 10:00 /home/ubuntu/bin/zhead

The first part shows the file permissions:

• r = readable
• w = writable
• x = executable

There’s no x in the example, so it’s not executable yet. (If the first character is d, it means the entry is a directory.)

4. Make the script executable

Add execute permissions for the user (the file’s owner):

chmod u+x ~/bin/zhead

Verify the change:

ls -l ~/bin/zhead

Example output:

-rwxr-xr-x 1 ubuntu ubuntu 123 Oct 19 10:00 /home/ubuntu/bin/zhead

Now the script has execute (x) permission.

5. Add ~/bin to your $PATH

Check whether ~/bin is already part of your $PATH:

echo $PATH

If you don’t see /home/ubuntu/bin or ~/bin in the list, you’ll need to add it.

Edit your .bashrc file:

nano ~/.bashrc

Add this line at the end:

export PATH="$HOME"/bin:"$PATH"

Press Ctrl+X, then Y, and Enter to save and exit.

6. Refresh your shell settings

Apply the changes without logging out:

source ~/.bashrc

7. Verify the changes

Check again:

echo $PATH

You should now see /home/ubuntu/bin (or ~/bin) at the start of your $PATH.

8. Test the script

Try running it:

zhead

You should see:

Error: No file supplied
Usage: zhead <gzipped-file>

Now test it with a gzipped file:

zhead /path/to/your/gzipped/file.gz

This should display the first 10 lines of the uncompressed file.

✅ Success! You’ve created a script and made it globally accessible through your $PATH.