Finding Commands (which, type)

Sometimes you need to know where a command is located or what type of command it is. which and type help you find this information.

which - Find Command Location

which shows the path to an executable:

which ls
which python
which bash

type - Command Classification

type tells you what kind of command something is:

type cd
type ls
type echo

Types of Commands

Type	Description	Example
Built-in	Part of the shell	cd, echo, pwd
Executable	Binary program	ls, grep, cat
Alias	Shortcut	ll -> ls -la
Function	Shell function	Custom functions
Keyword	Shell keyword	if, for, while

Why Does This Matter?

Understanding command types helps you:

• Debug issues with commands
• Know where programs are installed
• Understand shell behavior
• Write better scripts

which vs type

Feature	which	type
Shows path	Yes	Sometimes
Shows type	No	Yes
Built-ins	Not found	Found
Aliases	Not found	Found

Notice: which cd might say "not found" because cd is a shell built-in, not an executable.

Exercise: Find Command Type

Determine what type of command 'cd' is:

type Options

type -t ls              # Just the type word
type -a echo            # All locations
type -p ls              # Path only (like which)

Finding Multiple Commands

which ls cat grep       # Multiple at once
type ls cat grep        # Types of multiple commands

Checking if Command Exists

Useful in scripts:

# Check if command exists
if type python3 &> /dev/null; then
    echo "Python 3 is installed"
fi

whereis - Extended Search

whereis finds binaries, source, and man pages:

whereis ls
# ls: /bin/ls /usr/share/man/man1/ls.1.gz

Real-World Uses

Find Python Version

which python
which python3

Check Available Shells

which bash zsh fish

Verify Installation

which node       # Is Node.js installed?
which docker     # Is Docker installed?

Key Takeaways

• which finds the location of executables
• type shows what kind of command something is
• Built-in commands won't show in which
• Use type -a to see all definitions
• Essential for debugging and scripting