Bash

Running Scripts — bash, source, and the PATH

The difference between ./script.sh, bash script.sh, and source — and how to make your scripts available system-wide.

January 3, 20265 min read

BashScriptingPATH

There are multiple ways to run a Bash script, and the difference matters. Using the wrong method can mean your script runs in the wrong environment, or that variables and cd commands inside it don't affect your current shell.

Three Ways to Run a Script

Methods compared

Method	Subprocess?	Executable bit needed?	Notes
`./script.sh`	Yes	✅ Yes	Uses shebang interpreter
`bash script.sh`	Yes	❌ No	Forces bash, ignores shebang
`source script.sh`	No	❌ No	Runs in current shell — changes persist

./script.sh — Run in a Subshell

Running ./script.sh (or /path/to/script.sh) creates a child process (subshell). All commands run in that child process. When the script exits, the child dies — any variables it set or cd commands it ran are gone. Your current terminal is unaffected.

# demo.sh
cd /tmp
MY_VAR="hello"
echo "Inside script: $MY_VAR, PWD=$PWD"

echo "Before: PWD=$PWD"
./demo.sh
echo "After: PWD=$PWD, MY_VAR=$MY_VAR"
# PWD is unchanged, MY_VAR is empty — the subshell is gone

source — Run in the Current Shell

source script.sh (also written as . script.sh) does not create a subshell. The commands run directly in your current shell. Variables set and directories changed persist after the script finishes.

This is exactly how ~/.bashrc works — when you open a terminal, your shell sources that file to load your aliases and variables.

source demo.sh       # or equivalently:  . demo.sh
echo "After source: PWD=$PWD, MY_VAR=$MY_VAR"
# NOW: PWD=/tmp, MY_VAR=hello — changes stuck!

When to use source

Use source when a script needs to modify your current shell — like loading environment variables, activating a virtual environment, or defining functions you want to use interactively.

Don't use it for general task scripts — those should run in their own subprocess.

Making Scripts Available System-Wide

You can run a script from anywhere by placing it in a directory that's in your $PATH. ~/bin or ~/.local/bin are standard choices for personal scripts.

# Create ~/bin if it doesn't exist
mkdir -p ~/bin

# Copy or move your script there
cp hello.sh ~/bin/hello
chmod +x ~/bin/hello

# Add ~/bin to PATH in ~/.bashrc (if not already there)
echo 'export PATH="$HOME/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

# Now you can run it from anywhere
hello

Checking Syntax Without Running

bash -n script.sh    # parse and check syntax — does NOT run the script
bash -x script.sh    # run with debug output — prints each command before executing

Use -n before every commit

bash -n script.sh is a quick sanity check. It catches syntax errors like missing fi, unmatched quotes, and mis-spelled keywords before you run the script for real.

Quick Check

You write a script that sets MY_VAR='hello' and runs `cd /tmp`. After running it with `./script.sh`, what is true?