Shell Scripting: Environment Variables & Bash

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Master environment variables, variable assignment, and conditional logic in Bash. Learn how shells work, what PATH does, how to customize your prompt, and the critical dollar sign rule for variables. Commands are programs, PATH is everything, and the $ sign rule trips everyone up at first!

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At-a-glance checklist

• [ ] Use Bash specifically for all labs and coursework (different shells have different outputs)
• [ ] Understand environment variables store system-wide configuration (e.g., PATH)
• [ ] Use export to make variables available to child processes
• [ ] Learn PATH is a colon-separated list of directories for finding executables
• [ ] Customize your prompt with PS1 variable (u=user, h=host, w=directory)
• [ ] Recognize commands like ls are compiled programs, not built-in commands
• [ ] Variable assignment: NO spaces around = sign (name="value")
• [ ] Command substitution: variable=$(command) captures output
• [ ] Critical rule: NO $ when writing to variable, USE $ when reading from variable
• [ ] Use if [ condition ]; then for conditionals (spaces matter!)
• [ ] Connect to ECS servers via SSH for remote work

Key takeaways

The dollar sign rule: Think of $ as "get the value" - you write without $, you read with $. This trips up everyone initially!

Commands are programs: ls, grep, cat aren't magic - they're compiled executables stored in PATH directories. You could write your own!

PATH is everything: Shell searches PATH directories left-to-right to find commands. First match wins.

Bash for assessments: Different shells (zsh, fish, csh) have different syntax. Stick to Bash for consistency.