Finding Things

Finding files

find . -name "*.txt"            # files ending .txt, here and below
find /etc -name "*.conf"        # ...under /etc (may show "Permission denied" — normal)
find ~ -name "notes*" -type f   # files (not dirs) starting with "notes" in home

find walks the tree for real. It's thorough and slow on huge trees. For "where is this program," there's a faster tool:

which python3     # where is the python3 program?

Check: which ls prints /usr/bin/ls — the actual file that runs when you type ls.

Searching inside files

grep "error" app.log            # lines containing "error"
grep -r "hello" .               # -r: search every file under here
grep -i "error" app.log         # -i: ignore case
grep -n "error" app.log         # -n: show line numbers

grep is the single most useful text tool on Linux. Learn it before anything fancy.

Check: echo "hello linux" > t.txt && grep "hello" t.txt prints the matching line.

Asking for help

Three levels, in order:

ls --help        # quick summary of options (works for most commands)
man ls           # the full manual (arrows to scroll, q to quit)

man pages are complete but dense — written as reference, not tutorials. Read --help first; graduate to man when you need the full story. (The name is short for "manual," and yes, the joke about needing a manual for the manual is older than you.)

Not every command has --help spelled the same way (-h, -?), but most do.

A note on "Permission denied" from find

Searching under /etc or / will print Permission denied for directories you can't read. That's not an error in your command — it means those files aren't yours to see. Add 2>/dev/null to hide the noise:

find / -name "myfile.txt" 2>/dev/null

(The 2> sends error messages elsewhere; /dev/null is the void. More in Bash for Mere Mortals.)

Next: Processes