"command not found" for Your Own Scripts - PATH and chmod

2026-06-06 Reading time: About 10 min Difficulty: Intermediate

What You'll Learn

• Why only your own script says command not found
• How to tell command not found from Permission denied
• How to work through ./, chmod +x, PATH, and hash -r in order

Why does only my own script say command not found?

Conclusion: bash looks for a bare command name only in the directories listed in PATH. The current directory is not on PATH by default, so typing script.sh finds nothing.

When you type script.sh, bash resolves it in this order:

1. Shell functions, aliases, and builtins
2. Paths already cached in hash
3. The directories listed in the PATH environment variable (front to back)

If script.sh is in none of the PATH directories, you get command not found even when the file sits right in front of you.

$ ls
script.sh

$ script.sh
bash: script.sh: command not found

Leaving the current directory (.) off PATH is a deliberate safety default. If . were at the front of PATH, an attacker could drop a malicious file named like a real command (ls) into a directory you cd into, and you would run it by accident. So a script "right here" must be named explicitly.

How is command not found different from Permission denied?

Conclusion: command not found means "not located"; Permission denied means "located, but no execute permission." The message tells you which way to look.

These two have different causes and different fixes.

# The path is right, but there is no execute permission
$ ./script.sh
bash: ./script.sh: Permission denied

If adding ./ changes the error to Permission denied, the PATH problem is solved and the next issue is permissions. If you see bad interpreter, the shebang or line endings are at fault, so read Fixing "bad interpreter".

Run it with ./ first

Conclusion: Run a script in the current directory with ./script.sh. The ./ is an explicit path that skips the PATH search entirely.

# NG: only PATH is searched, so it is not found
$ script.sh
bash: script.sh: command not found

# OK: name the file in the current directory directly
$ ./script.sh
Hello

If it lives elsewhere, use an absolute or relative path instead.

$ /home/alice/tools/script.sh
$ ~/tools/script.sh
$ bash script.sh        # passing it to bash works even without the execute bit

What happens without execute permission?

Conclusion: Without the execute bit, ./script.sh stops with Permission denied. Grant it with chmod +x.

Newly created, downloaded, or copied scripts often lose their execute permission.

$ ls -l script.sh
-rw-r--r-- 1 alice alice 42 Jun  6 10:00 script.sh

$ ./script.sh
bash: ./script.sh: Permission denied

-rw-r--r-- has no x (execute bit). Add it.

$ chmod +x script.sh
$ ls -l script.sh
-rwxr-xr-x 1 alice alice 42 Jun  6 10:00 script.sh

$ ./script.sh
Hello

How do I add my own directory to PATH?

Conclusion: To avoid typing ./ every time, add your script directory to PATH. Put export PATH in ~/.bashrc to make it permanent.

First, check the current PATH.

$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin

Add the directory where you keep scripts (for example ~/bin).

# For this session only (current shell)
$ export PATH="$HOME/bin:$PATH"

To make it permanent, append it to ~/.bashrc (or ~/.profile for login shells).

# Add to the end of ~/.bashrc
export PATH="$HOME/bin:$PATH"

# Reload it into the current shell
$ source ~/.bashrc

$ which script.sh
/home/alice/bin/script.sh

$ script.sh        # runs without ./
Hello

Still not found, or grabbing the old binary?

Conclusion: bash caches the path of a command once it finds it (hash). Right after you move or replace a script, it may grab the old path. Clear the cache with hash -r.

When PATH and permissions look right but behavior is wrong, use type to see what bash actually intends to run and from where.

$ type -a script.sh
script.sh is /home/alice/bin/script.sh

If type points at an old location, or a command you deleted still runs, the cache is stale.

# Clear the cached command paths
$ hash -r

# Check again
$ type -a script.sh