CLI Commands

Commands Summary

Command	Purpose
head	Display the first few lines of a file or input
tail	Display the last few lines of a file or input
cut	Extract specific portion from each row of a file or input
grep	Filters rows having a specified pattern in a file or input
sed	Stream editor used to find, replace and delete patterns in a file
awk	Pattern search and processing language
less	A pager that displays text files with scroll
cat	Displays a file
xargs	Converts input from stdin into arguments for a command
sort	Sorts a file or input
pwd	Print current working directory
ls	list files and folders in a directory
echo	Print a message to stdout
man	Show a commands manual
history	Show command history
clear	Clear command console
netstat	Show system’s network info (routing & sockets)
ifconfig	Show system’s network interface config
wget	Download files from a URL
ping	Send a connection request to a server, used to check network connectivity
shutdown	Shutdown system
ps	List running processes
pkill	Kill a running process
systemctl	Manage system services
time	Calculate command execution time
uname	Print info of the system kernel
chmod	Change permissions of a file
chown	Change ownership of a file
cd	Change working directory
mv	Move files
cp	Copy files
rm	Delete files
mkdir	Makes a new directory
rmdir	Deletes an empty directory
touch	Creates a new file
sudo	Runs a command as a superuser
xdg-open	Open file or URL using the default application
count	Returns row count
whoami	Print current user

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Cut

ls -l | cut -d ' ' -f1-3  # prints fields 1,2 & 3 based on the space delimiter 
 
ls -l | cut -b1-2  # prints first 2 bytes of every line

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Sed

# Replace all first occurences of 'unix' with 'linux' 
# in all lines
sed 's/unix/linux/' sample.txt
 
# s - indicates substitution
# / - delimiter
 
# To replace all occurences
sed 's/unix/linux/g' sample.txt

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Awk

# Signature: awk '<Pattern> {<command>}' <file>
# start and end regex with '/'
 
# Print lines having the pattern 
awk '/option/ {print}' sample.txt 
 
# From the input stream
cat sample.txt | awk '/option/ {print}'
 
# Print 1st & 3rd column of lines with the pattern 
# with row number
awk '/option/ {print NR " - " $1 $3}' sample.txt 
 
# Print number of lines
awk 'END {print NR}' sample.txt 
 
# Number of .md files in my vault
find -name '*.md' -type f | awk 'END {print NR}'
 
# Get URLs of all image previews in a mardown file
cat file.md | awk 'match($0, /!\[\]\(([^)]+)\)/, arr) { gsub(/[()]/, "", arr[1]); print arr[1]}'

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Xargs

# Total number of lines in .md files in my vault
find -name '*.md' -type f -print0 | xargs -0 cat | awk 'END {print NR}'
 
# Get line count of each file
find -name '*.md' -type f -print0 | xargs -0 wc -l