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Linux shell
How do I inspect and change system state through commands?
Shell vocabulary, paths, standard command patterns and safe observation in Linux.
- Last verified
- 2026-09-20
- Review interval
- 180 days
- Status
- In review
01 / Overview
How do I inspect and change system state through commands?
A shell reads commands, expands their syntax and starts programs or built-in operations. Learning the current directory, paths, arguments and observable output creates the foundation for later administration and security work.
03 / Concepts
Concepts
- Current directoryshell-current-directory
- The directory used as the starting point for relative paths.
- Pathshell-path
- A location expressed as a sequence of filesystem names.
- Output and resultshell-output
- Displayed text is one observation; exit status and changed state are separate evidence.
04 / Commands
Commands
| Environment | Command | Purpose | Lab |
|---|---|---|---|
| linux | pwd | Print the current directory. | Available in Command Lab |
| linux | ls | List directory entries. | Available in Command Lab |
| linux | cd notes | Change the current directory. | Available in Command Lab |
| linux | cat notes/dns.txt | Read the simulated text file in Command Lab. | Available in Command Lab |
05 / Labs
Labs
- Command LabOpen safe simulator →
Deterministic browser simulator for CMD, Linux shell and PowerShell practice with virtual state.
deterministic simulator
07 / Security
Security
- Read the command, options, arguments, working directory and expected effect before execution; copied commands are untrusted input.
08 / Troubleshooting
Troubleshooting
- When a path fails, inspect the current directory and distinguish relative from absolute paths before changing permissions.
09 / Quick checks
Quick checks
- Which command tells you the starting point for a relative path?
10 / GRAPH
Related concepts
- Windows CMD
- PowerShell →
- Process
- DNS →
Used in certifications
These links reuse canonical knowledge; the certification page does not own or duplicate the topic.
12 / Sources and freshness
Sources and freshness
- Last verified
- 2026-09-20
- Review interval
- 180 days
- Source version
- GNU Bash manual · GNU Coreutils manual · Command Lab grammar v1