Pathpath

PATH variable explained #

The $PATH variable #

  • lists directories to search fro executables
  • only contains the directory paths where executables live
  • itself never contains any executables (like “python”)

See all directories in your PATH #

echo $PATH | tr ':' '\n'

We see directories like:

/usr/local/bin
/usr/bin
/opt/homebrew/bin
/bin

Executables INSIDE those directories: ls /usr/local/bin | grep python ls /opt/homebrew/bin | grep python ls /usr/bin | grep python

This shows the first python3 found in PATH #

which python3 – /usr/local/bin/python3

This shows ALL python3 executables in PATH #

which -a python3 – /usr/local/bin/python3 – /usr/bin/python3

How it works? #

When we type python3, our shell:

  • Looks in /usr/local/bin/ for a file called python3
  • If found, executes it
  • If not found, moves to next directory (/usr/bin/)

What’s actually in /usr/local/bin/ #

ls -l /usr/local/bin/python*

You’ll see symlinks (shortcuts):

python3 -> ../../../Library/Frameworks/Python.framework/Versions/3.11/bin/python3
python3.11 -> ../../../Library/Frameworks/Python.framework/Versions/3.11/bin/python3.11

You type: python3
    ↓
Shell finds: /usr/local/bin/python3 (symlink)
    ↓
Symlink points to: /Library/Frameworks/Python.framework/Versions/3.11/bin/python3
    ↓
This is the actual Python executable

ls -l /usr/local/bin/python*

Follow the chain #

readlink /usr/local/bin/python3

See the actual executable #

realpath /usr/local/bin/python3

Where is the default Python version set? #

There’s no single configuration file - it’s determined by which symlink exists first in the PATH:

Edit directories order #

export PATH="/usr/local/bin:$PATH"

This puts /usr/local/bin FIRST, so it’s searched before /usr/bin

How to change your default Python? #

Modify your PATH order # 

export PATH="/opt/homebrew/bin:$PATH"
source ~/.zshrc
# Now python3 will find Homebrew's version first

Use version-specific commands #

python3 python3.11 python3.12

Why directories order may be confusing # 

cho $PATH | tr ':' '\n' | nl

     1  /.nvm/versions/node/v23.6.1/bin
     2  /.rd/bin
     3  /google-cloud-sdk/bin
     4  /opt/homebrew/bin
     5  /opt/homebrew/sbin
     6  /usr/local/bin
     7  /System/Cryptexes/App/usr/bin
     8  /usr/bin
     9  /bin
    10  /usr/sbin
    11  /sbin

Homebrew Python may not be your default even though /opt/homebrew/bin comes first.

The key issue: What’s IN those directories

Check what’s in /opt/homebrew/bin #

ls -la /opt/homebrew/bin/python*

Check what’s in /usr/local/bin #

ls -la /usr/local/bin/python*

Results #

/opt/homebrew/bin/ may have:

  • python3.12 ✅
  • python3.13 ✅
  • NO python3 ❌

/usr/local/bin/ may have:

  • python3 ✅ (symlink to python.org 3.11)
  • python3.11 ✅

What happens when you type python3 #

Shell searches in PATH order for a file named “python3”:

  1. /opt/homebrew/bin/python3 → NOT FOUND (only python3.12, python3.13)
  2. /usr/local/bin/python3 → FOUND! (stops here)

Switch python version #

From .zshrc

# Switch to 3.9.6
export PATH="/usr/bin:$PATH"
source ~/.zshrc
python3 --version  # 3.9.6

# Switch to 3.12
export PATH="/opt/homebrew/opt/python@3.12/libexec/bin:$PATH"
source ~/.zshrc
python3 --version  # 3.12.x
Jan 18, 2026