Useful Linux tools

Search and extract

Command	Use	Example
awk	Complex text processing, often used for structured data	awk
grep	Search for specific data, can use Regex	grep -i "fail" /var/log/auth.log
cut	Trim and extract parts of a document, such as sections of columns	cut -d':' -f1 /etc/passwd

Modify and replace

Command	Use	Example
sed	Modify and replace text in files	sed "s/hello/hi/g" ./my_textfile.txt
tr	Translate or delete characters in text	tr 'A-Z' 'a-z' < input.txt > output.txt

Sort and count

Command	Use	Example
wc	Counts lines, words, chars	wc -l /var/log/syslog
sort	Arranges in logical order	sort -t: -k,3 -n -r /etc/passwd
uniq	Filters duplicates	sort /var/log/auth.log | uniq -c
xargs	Builds and executes further commands, used to process output from other commands in bulk	find /home/logs | xargs -I {} -n 1 -p -t cp {} /backup/logs

View and navigate

Command	Use	Example
head	Displays the beginning of a file	head -n 50 /etc/apache2/httpd.conf
tail	Show the end of a file, often to monitor in real time	tail -n 20 -f /var/log/syslog
more	View a long file one page at a time	cat /var/log/syslog | more
less	Like more but includes a few other options	cat /etc/passwd | less

Output and redirect

Command	Use	Example
echo	Displays whatever is specified as output or to a file	echo "$(date):System update completed >> /var/log/update.log
cat	Reads and merges files	cat log1.txt log2.txt log3.txt > full_log.txt
tee	Takes input and writes it a file and displays output to screem	ping -c 4 google.com | tee -a network_log.txt

Math and format

Command	Use	Example
printf	Print formatted; allows for format specifiers	printf "var1: %s\tvar2: %s\n" "$VAR1" "$VAR2"
bc	Basic calculator, particularly good for floating point	echo '5 / 3' | bc

System and scripts

Command	Use	Example
uname	Used to retrieve system information	echo "System Info: $(uname -a)" >> /var/log/update.log
source	Used to execute scripts in the current shell session	source /path/to/file