The command line feels intimidating until you realize most real work uses a tiny core of commands, glued together. Master these categories and you can operate any Unix-like system:

• Look around: ls, pwd, cat, less, head, tail
• Find things: find, grep, which
• Move data: cp, mv, rm, mkdir
• Inspect the system: ps, top, df, free
• Combine commands: the pipe | and redirection >

The real superpower is composition: small tools that each do one thing, piped together to answer a question. cat access.log | grep 404 | wc -l counts your 404 errors — three simple tools forming an answer.

Say a service is misbehaving and you want to see what’s eating memory and find recent errors:

# Top 5 memory-hungry processes
ps aux --sort=-%mem | head -n 6

# How much disk is free?
df -h

# Find ERROR lines from today's app log and show the last 20
grep -i error /var/log/myapp.log | tail -n 20

# Count how many times each IP hit the server (classic one-liner)
awk '{print $1}' access.log | sort | uniq -c | sort -rn | head

Notice the pattern: generate a stream of text, filter it, then summarize. That shape solves a huge fraction of day-to-day ops problems.

1. Use history | grep cd to find every cd command you’ve run this session.
2. Create a file with three lines, then show only the middle line using a combination of head and tail.
3. Use grep -rn "TODO" . to find every TODO comment in a project folder, with file names and line numbers.
4. Pipe ls -l into wc -l to count how many items are in a directory.

• ↗ Bash Reference Manual
• ↗ explainshell (decode any command)