A Bash cheat sheet for various tasks on Ubuntu-based distros.

cheat.sh

# Add a string to the beginning of each line in a file:
awk '{ print "prefix" $0 }' PATH-TO-FILE

# Append a directory to the PATH environment variable:
PATH="${PATH:+${PATH}:}/path/to/directory"

# Change author for last N Git commits:
git rebase -i HEAD~N -x "git commit --amend --author 'Author Name <author.name@mail.com>' --no-edit"

# Change the password of a Linux user account:
[sudo] passwd [USERNAME]

# Clean all files not tracked by Git, including those present on ignore lists:
git clean -dfx

# Compress a PDF file:
ps2pdf -dPDFSETTINGS=/ebook PATH-TO-INPUT.pdf PATH-TO-OUTPUT.pdf

# Create a PEM file from a PPK file:
[sudo] apt-get update && [sudo] apt-get install putty-tools
puttygen INPUT-FILE.ppk -O private-openssh -o OUTPUT-FILE.pem

# Create a symbolic link to a given file:
[sudo] ln -s PATH-TO-FILE PATH-TO-LINK

# Delete a directory and all of its contents:
[sudo] rm -rf PATH-TO-DIRECTORY

# Delete all subdirectories with a specific name:
find PARENT-DIRECTORY -type d -name "SUBDIRECTORY" -exec rm -rf {} +

# Delete KDE icons cache:
rm ~/.cache/icon-cache.kcache

# Disable a service from starting on boot:
[sudo] systemctl disable SERVICE-NAME

# Display current system time, date, and timezone:
## If your system was booted using systemd, use:
timedatectl

## Otherwise, use:
date

# Download all PDF files from a web page:
wget -r -A.pdf WEB-PAGE-URL

# Export GPG private key:
gpg --export-secret-key KEY-ID > KEY-FILE

# Export GPG public key:
gpg --export KEY-ID > KEY-FILE

# Fast-copy files/directories:
[sudo] rsync --info=progress2 -auvz PATH-TO-SOURCE PATH-TO-DESTINATION

# Find common lines between 2 text files:
grep -iFxf PATH-TO-FIRST-FILE PATH-TO-SECOND-FILE

# Find running processes matching a specific pattern:
psgrep -la PROCESS-PATTERN

# Get the SHA256 fingerprint of an SSH key:
ssh-keygen -lf PATH-TO-SSH-KEY

# Import GPG public/private key:
gpg --import KEY-FILE

# List all enabled software repositories:
grep ^deb /etc/apt/sources.list /etc/apt/sources.list.d/*

# List all environment variables:
printenv

# List all Git branches containing a specific commit:
git branch --contains COMMIT_HASH

# List all TCP connections from a specific IP address
netstat -t | grep IP-ADDRESS

# List available memory hardware:
[sudo] lshw -c memory

# List local Git tags:
git tag -n

# List installed packages:
apt list --installed

# List network interfaces:
ip link show

# List OS version details:
cat /etc/os-release

# Parse a CSV file using GNU awk:
gawk -vFPAT='[^,]*|"[^"]*"' '{ print $1 }'

# Remove all quotes from a string using awk:
awk '{ gsub(/"/, "", $0); print $0 }'

# Skip the first line in a file when using awk:
awk 'NR>1 { print $0 }'

# Test whether a port on a remote machine is reachable:
nc -v HOSTNAME|IP-ADDRESS PORT

# Truncate a specific file:
[sudo] cat /dev/null > PATH-TO-FILE

# Update all snap packages:
[sudo] snap refresh

# Verify the GPG signature of a Git commit:
git verify-commit COMMIT-HASH