# Files and Text

## Basic file operations

- `touch <file>` — create an empty file (or update its timestamp if it exists)
- `mkdir <dir>` — create a directory (`-p` creates any missing parent directories too)
- `cp <src> <dst>` — copy a file
- `mv <src> <dst>` — move OR rename a file (Linux treats renaming as "moving to a new name in
  the same place")
- `rm <file>` — delete a file (`-r` for a directory, `-f` to skip confirmation — dangerous
  combined: `rm -rf` deletes without asking, permanently)

## Reading text

- `cat <file>` — print the whole file at once
- `less <file>` — page through a file interactively (press `q` to quit) — the right tool for
  anything too long to read in one screen
- `head <file>` / `tail <file>` — the first/last 10 lines by default (`-n 20` for a different
  count); `tail -f` follows a file live as new lines are appended — exactly how you'd watch a
  log file update in real time

## Searching text: `grep`

`grep PATTERN file` prints only the lines matching PATTERN. This is one of the most-used
commands in real operations work — "find the lines that matter" beats "read everything."

## Pipes and redirection: composing commands

- **A pipe (`|`)** sends one command's output as the next command's input:
  `cat app.log | grep ERROR` — read the file, then filter it.
- **Redirection (`>`)** sends a command's output into a file instead of the screen (overwriting
  it): `grep ERROR app.log > errors.txt`. `>>` appends instead of overwriting.

## stdout vs. stderr

A command actually has TWO separate output streams: **stdout** (normal output) and **stderr**
(error messages), even though both print to your screen by default. This is why
`command 2>/dev/null` (redirecting stream `2`, stderr, to nowhere) can suppress error noise
while still showing normal output — you'll use exactly this pattern in later Labs.

## Instructor Notes

**Lesson goal:** Build real fluency composing small commands together — this is the single
highest-leverage Linux skill for troubleshooting work later in ROOT_.

**Approximate timing:** 15 minutes read; 10 minutes live.

**Common misconception to watch for:** students often don't realize stdout/stderr are separate
streams until they see `2>/dev/null` change what's suppressed — worth demonstrating live.

**Demo idea:** run a command that produces both real output and an error in the same call
(e.g. `ls /etc /nonexistent`) and show how `2>/dev/null` changes what appears.