How do I search for text inside files in Linux?

Use grep: 'grep "pattern" file.txt' to search in one file, 'grep -r "pattern" /directory' to search recursively, 'grep -i "pattern" file' for case-insensitive search, 'grep -n "pattern" file' to show line numbers, 'grep -v "pattern" file' to show lines NOT matching. Combine with pipes: 'cat file | grep "pattern"'.

Linux Commands Cheat Sheet — Essential Bash Reference for Developers

Q: What are the most important Linux commands to know?

The most important Linux commands are: ls (list files), cd (change directory), pwd (print working directory), cp (copy), mv (move/rename), rm (remove), mkdir (make directory), grep (search text), chmod (change permissions), ps (list processes), kill (stop process), and ssh (remote login). These 12 commands cover 80% of everyday terminal usage.

Q: How do I find a file in Linux?

Use 'find / -name filename' to search the entire filesystem, or 'find . -name filename' to search from the current directory. For faster searches, use 'locate filename' (requires the locate database to be updated with 'updatedb'). To find files by content, use 'grep -r "search term" /path/to/search'.

Q: How do I check disk space in Linux?

Use 'df -h' to see disk space usage for all mounted filesystems in human-readable format. Use 'du -sh /path' to see the total size of a specific directory. Use 'du -sh *' inside a directory to see the sizes of all items in that directory.

Q: How do I kill a process in Linux?

First find the process ID with 'ps aux | grep processname' or 'pgrep processname'. Then use 'kill PID' to send SIGTERM (graceful stop) or 'kill -9 PID' to force kill. You can also use 'pkill processname' to kill by name, or 'killall processname' to kill all processes with that name.

Q: How do I change file permissions in Linux?

Use chmod to change permissions. Common patterns: 'chmod 755 file' (owner: rwx, group: rx, others: rx), 'chmod 644 file' (owner: rw, group: r, others: r), 'chmod +x file' (add execute for all), 'chmod -R 755 dir' (recursive). Permissions are read(4), write(2), execute(1) added together for owner/group/others.

Q: How do I use pipes and redirects in Linux?

Pipes (|) send output of one command to input of another: 'ls -la | grep .txt | wc -l' counts .txt files. Redirects: '>' overwrites a file (echo 'hello' > file.txt), '>>' appends to a file, ' ' redirects stderr, '2>&1' combines stderr with stdout. Example: 'command > output.txt 2>&1' saves all output including errors.

Q: What is the difference between apt, yum, and dnf?

These are package managers for different Linux distributions. apt (and apt-get) is used on Debian/Ubuntu systems. yum is used on older RHEL/CentOS systems. dnf is the modern replacement for yum, used on Fedora, RHEL 8+, and CentOS 8+. For macOS, use brew (Homebrew). The commands are similar: install, update, remove — just the package manager name differs.

Tip: Press Ctrl+K to focus search. Click any command to copy it to clipboard. Use category filters to narrow results.

⚡ Power User Tips

Chain commands with &&

Run the next command only if the previous succeeded: mkdir project && cd project && git init

Run in background with &

Add & at the end: python server.py &. Use jobs to list, fg %1 to bring to foreground.

Use !! for last command

Forgot sudo? Run sudo !! to repeat the last command with sudo. !$ gives the last argument.

Navigate history fast

Press Ctrl+R to reverse-search command history. Type part of any previous command to find it.

Create command aliases

Add to ~/.bashrc: alias ll='ls -la', alias gs='git status'. Run source ~/.bashrc to apply.

Redirect stderr too

command 2>&1 | tee output.log — captures both stdout and stderr while also showing them in the terminal.

Use curly braces for expansion

cp file.txt{,.bak} copies file.txt to file.txt.bak. mkdir -p src/{css,js,img} creates multiple dirs.

Screen / tmux for persistence

Use tmux new -s session or screen to keep processes running after SSH disconnect. Detach with Ctrl+B, D.

Frequently Asked Questions

What are the most important Linux commands to know?

The core commands every Linux user needs: ls, cd, pwd, cp, mv, rm, mkdir, grep, chmod, ps, kill, and ssh. These 12 commands cover 80% of everyday terminal usage. Learn them well before diving into more specialized tools.

How do I find a file in Linux?

Use find . -name "filename" to search from the current directory. Add -type f for files only, -type d for directories. For faster searches, use locate filename (requires running updatedb first). To find files by content, use grep -r "search term" /path.

How do I check disk space in Linux?

df -h shows disk usage for all mounted filesystems in human-readable format. du -sh /path shows the size of a specific directory. du -sh * inside a directory shows sizes of all items. du -sh * | sort -rh | head -10 shows the 10 largest items.

How do I kill a process in Linux?

First find the PID with ps aux | grep processname or pgrep processname. Then: kill PID for graceful stop (SIGTERM), kill -9 PID to force kill (SIGKILL). Shortcuts: pkill processname kills by name, killall processname kills all processes with that name.

How do I change file permissions in Linux?

Use chmod. Common patterns: chmod 755 file (executable, readable by all), chmod 644 file (readable by all, writable only by owner), chmod +x file (add execute permission), chmod -R 755 dir (recursive). Permissions: read=4, write=2, execute=1. Add them together for owner/group/others.

How do I use pipes and redirects in Linux?

Pipes (|) pass output to another command: ls -la | grep .txt | wc -l. Redirects: > writes to file (overwrites), >> appends, < reads from file. 2> redirects stderr, 2>&1 combines stderr with stdout. Example: command > out.txt 2>&1 captures everything.

How do I search for text inside files?

grep "pattern" file.txt — search one file. grep -r "pattern" /dir — recursive search. grep -i — case-insensitive. grep -n — show line numbers. grep -v — show non-matching lines. grep -l — show only filenames. Combine: grep -rn "TODO" . --include="*.py"

What is the difference between apt, yum, and dnf?

These are package managers for different Linux distros. apt / apt-get: Debian, Ubuntu, Mint. yum: older RHEL, CentOS 7. dnf: modern Fedora, RHEL 8+, CentOS 8+. pacman: Arch Linux. brew: macOS (Homebrew). The basic workflow is similar: install, update, search, remove — only the package manager name differs.