Phase 0: Command Line & OS Literacy · ~35 minutes · Terminal · chmod · PATH

Permissions, Processes, and Environment Variables

"command not found" almost never means it didn't install. It usually means it installed somewhere your shell isn't looking.

Hiring signal: Diagnoses 'command not found' and 'permission denied' by checking the actual cause, not by reinstalling or chmod-ing blindly

What you will learn

Read and set file permissions with chmod, in both symbolic and octal notation
Explain $PATH as the ordered list of places the shell looks for commands
Diagnose 'installed but not on PATH' as distinct from 'not actually installed'
Predict who can read/write/execute a file from its permission string

Introduction

Type: Learn Languages: Bash / Zsh Prerequisites: Lesson 02 (Reading, Filtering, and Combining Text) Time: ~35 minutes

Objective

Learning objectives

Read and set file permissions with chmod, in both symbolic and octal notation
Explain $PATH as the ordered list of places the shell looks for commands
Diagnose "installed but not on PATH" as distinct from "not actually installed"
Predict who can read/write/execute a file from its permission string

What you're building

A script greet.sh that prints a short greeting:

Create it, confirm with ls -l that it initially lacks execute permission, and confirm running it directly fails with Permission denied
Fix it with chmod +x, confirmed by both ls -l and successfully running ./greet.sh
Move it to a directory that is not currently on your $PATH (create one if needed), confirm running it by bare name (greet.sh) fails with command not found even though it exists and is executable
Add that directory to $PATH for your current session and confirm greet.sh now runs by bare name
Record every command and its real output in path_notes.txt, plus one sentence distinguishing what problem each of the two errors actually indicated

A file's permission string is -rwxr-x---. Who can execute this file?

Reading the three groups: owner is rwx (full access, including execute), group is r-x (read and execute, no write), other is --- (nothing at all). Execute permission (the x) is present for owner and group, absent for everyone else — so the owner and the file's group can run it, but no one outside that group can, matching a common real setting for a team-shared script that shouldn't be world-runnable.

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