What is the difference between grep -v and grep -i?

-v inverts the match (shows lines that do NOT contain the pattern), while -i makes the match case-insensitive. You can combine them: grep -vi 'error' log.txt shows lines without 'error' regardless of case.

How do I find files modified in the last 24 hours?

Use find with the -mtime option: find /path -mtime -1 finds files modified within the last 24 hours. Use -mtime -7 for the last week. The minus sign means 'less than N days ago'.

What is the difference between > and >> for output redirection?

> overwrites the file with new content (creating it if it doesn't exist), while >> appends to the end of the file. For example, echo 'line' > file.txt replaces the file, echo 'line' >> file.txt adds a line.

How do I run a command in the background and keep it running after logout?

Use nohup with & at the end: nohup python server.py > output.log 2>&1 &. The nohup prevents the process from being killed when you log out, and > output.log 2>&1 redirects both stdout and stderr to a log file.

What is the difference between kill and pkill?

kill requires the process ID (PID): kill -9 1234. pkill matches by process name: pkill nginx kills all nginx processes. pkill -f matches against the full command line, useful for scripts or Python processes.

Linux Commands Reference

Searchable Linux CLI command reference with categories, examples, and one-click copy.

File & Directory

Command	Syntax	Description	Example
ls	ls [options] [path]	List directory contents	ls -la /home
cd	cd [dir]	Change directory	cd /var/log
pwd	pwd	Print working directory	pwd
mkdir	mkdir [-p] dir	Create directory (use -p for nested)	mkdir -p a/b/c
rm	rm [-rf] path	Remove files/directories	rm -rf old_dir
cp	cp [-r] src dst	Copy files/directories	cp -r src/ dst/
mv	mv src dst	Move or rename files	mv old.txt new.txt
find	find path -name pattern	Find files by name/attribute	find . -name '*.log'
ln	ln [-s] src link	Create hard/soft link	ln -s /opt/app app
chmod	chmod mode file	Change file permissions	chmod 755 script.sh
chown	chown user:group file	Change file ownership	chown www-data:www-data index.html

Text Processing

Command	Syntax	Description	Example
cat	cat [file]	Concatenate and print file content	cat /etc/hosts
grep	grep [options] pattern file	Search for patterns in files	grep -rn 'error' /var/log
sed	sed 's/old/new/g' file	Stream editor — find and replace	sed -i 's/foo/bar/g' config.txt
awk	awk '{print $1}' file	Pattern scanning and processing	awk -F: '{print $1}' /etc/passwd
sort	sort [options] file	Sort lines in a file	sort -k2 -n data.txt
uniq	uniq [options] file	Remove duplicate lines	sort file \| uniq -c
wc	wc [-l\|-w\|-c] file	Word, line, and char count	wc -l access.log
head	head [-n N] file	Print first N lines	head -20 app.log
tail	tail [-n N] [-f] file	Print last N lines; -f to follow	tail -f /var/log/syslog
cut	cut -d'sep' -f n file	Extract fields from lines	cut -d',' -f1 data.csv

Process Management

Command	Syntax	Description	Example
ps	ps [aux]	List running processes	ps aux \| grep nginx
top	top	Interactive process viewer	top
htop	htop	Enhanced interactive process viewer	htop
kill	kill [-9] PID	Send signal to process (9=force kill)	kill -9 1234
pkill	pkill name	Kill processes by name	pkill -f gunicorn
jobs	jobs	List background jobs in current shell	jobs -l
bg	bg [%n]	Resume job in background	bg %1
fg	fg [%n]	Bring job to foreground	fg %1
nohup	nohup cmd &	Run command immune to hangups	nohup python server.py &
systemctl	systemctl [start\|stop\|status] svc	Manage systemd services	systemctl restart nginx

Networking

Command	Syntax	Description	Example
ping	ping [-c n] host	Send ICMP echo requests	ping -c 4 google.com
curl	curl [options] url	Transfer data from/to server	curl -I https://example.com
wget	wget url	Download files from web	wget https://example.com/file.tar.gz
ssh	ssh user@host	Secure remote shell login	ssh user@192.168.1.10
scp	scp src user@host:dst	Secure copy over SSH	scp file.txt user@host:/tmp/
rsync	rsync -avz src dst	Sync files locally or over SSH	rsync -avz src/ user@host:/backup/
netstat	netstat -tuln	List network connections/ports	netstat -tuln \| grep :80
ss	ss -tuln	Socket statistics (modern netstat)	ss -tlnp
ip	ip addr / ip route	Manage network interfaces/routes	ip addr show eth0
dig	dig [type] domain	DNS lookup	dig MX example.com

Archiving

Command	Syntax	Description	Example
tar	tar [-czf\|-xzf] archive files	Create/extract tar archives	tar -czf backup.tar.gz /data
zip	zip archive files	Create ZIP archive	zip -r site.zip public/
unzip	unzip archive	Extract ZIP archive	unzip archive.zip -d output/
gzip	gzip file	Compress file with gzip	gzip large.log
gunzip	gunzip file.gz	Decompress gzip file	gunzip large.log.gz

Disk & Memory

Command	Syntax	Description	Example
df	df -h	Disk space usage of filesystems	df -h /
du	du -sh path	Disk usage of directory	du -sh /var/log
free	free -h	Show free and used memory	free -h
lsblk	lsblk	List block devices	lsblk -f
mount	mount dev mountpoint	Mount filesystem	mount /dev/sdb1 /mnt/data

About this tool

The Linux Commands Reference is a comprehensive searchable database of command-line tools and utilities for Unix-like systems. Whether you're a system administrator, DevOps engineer, or developer working in a terminal-heavy environment, this tool provides instant access to command syntax, options, and real-world examples without leaving your browser.

Simply search for a command by name or browse through categories like file management, system administration, networking, and development tools. Each entry displays the command syntax, common flags and options, practical usage examples, and descriptions of what each parameter does. The one-click copy feature lets you instantly copy any command or example to your clipboard for immediate use in your terminal.

Frequently Asked Questions

Code Implementation

import subprocess
import os

# Run a shell command and capture output
result = subprocess.run(
    ["ls", "-la", "/home"],
    capture_output=True,
    text=True
)
print(result.stdout)

# Search for files (equivalent to find)
import pathlib
# Find all .log files modified in last 24h
import time
now = time.time()
for path in pathlib.Path("/var/log").rglob("*.log"):
    if now - path.stat().st_mtime < 86400:
        print(path)

# Grep equivalent
import re
with open("/etc/hosts") as f:
    for line in f:
        if re.search(r"127\.\d+\.\d+\.\d+", line):
            print(line.strip())

# Process management
import psutil
for proc in psutil.process_iter(['pid', 'name', 'cpu_percent']):
    try:
        if proc.info['cpu_percent'] > 10:
            print(f"PID {proc.info['pid']}: {proc.info['name']}")
    except psutil.NoSuchProcess:
        pass

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