Common unix commands I have used and put together for quick reference.

Navigation

Command/Flag	Explanation
cd ~	Changes the directory to the home.
cd directory-name	Changes the directory to the specified one.
cd ..	Moves up one directory.
cd -	Switched back to the previous directory.
ls	Lists the contents of the current directory.
ls -a	Lists the contents of the current directory including invisible files/directories.
ls -l	Lists the contents of the current directory vertically with file size, permissions, etc.
ls -F	Lists the contents of the current directory with "/" after sub-directories.
ls -X	Lists the contents of the current directory sorted by file extension, then alphabetically.
ls *.ext	Lists only the files with the extension ".ext", works with any extension.
mkdir name	Creates a new directory with the specified name.
vim filename	Opens a text file with the vim editor (":q!" to exit if unfamiliar with vim).
pwd	Prints the current directory path.
chmod +x filename	Adds executable permission to a file.
chmod +r filename	Adds read permission to a file.
chmod +w filename	Adds write permission to a file.
cat filename	Displays a text file in the terminal.
grep "expression"	Searches for all instances of the expression in the current directory.
head filename	Displays the first 10 lines of a file.
tail filename	Displays the last 10 lines of a file.

Moving, removing, and copying files.

Command/Flag	Explanation
mv oldname newname	Rename the old file to the new filename.
mv filename /path/to/new/location	Moves the file to the specified path.
rm filename	Removes the file.
rm *	Removes everything in the directory.
rm -r directory-name	Removes everything inside a directory, then removes the directory.
rmdir directory-name	Removes an empty directory.
cp oldfile newfile	Copies the old file into one with the new name.
cp file destination/to/go	Copies the file to the new destination.

SSH and SCP

Command/Flag	Explanation
ssh username@target-host	Connects to the target host using the secure shell.
scp username@target-host:~/path/to/file .	Copies the file from the remote server to the current directory.
scp -r username@target-host:~/path/to/directory .	Copies all the contents of the directory on the remote server to the current directory.
scp username@target1:~/path/to/source/file username@target2:~/path/to/copy/location	Copies the file from target 1 to the directory in target 2.

Git

Command/Flag	Explanation
git init project-name	Initializes a directory with a .git folder inside it.
git init --bare project-name	Initializes a bare repository with the project name.
git clone link-to-repository	Creates a git repository copy from a remote source.
git status	Shows the status of the local copy of the repository.
git diff	Shows the changes that have not been added to the index, i.e. not staged.
git add/stage filename	Adds the file changes to your index.
git add/stage *	Adds all file changes to your index.
git commit -m "Message"	Commits the changes in the index with the message given.
git commit --amend	Adds the current staged changes to the last commit for the repository.
git stash	Saves the local changes while reverting the working tree back to the HEAD.
git stash apply	Restores the changes from the last stash, without removing them from the stash list.
git stash pop	Restores the changes from the last stash, removing them from the stash list.
git stash clear	Deletes all current stashes.
git reset	Unstages files after they have been added/staged.
git reset HEAD~	Cancels the last commit, but keeps the changes in the working tree so your work is not lost.
git clean	Removes all untracked files and cleans the working tree.
git push	Pushes the latest commit to the remote repository.
git pull	Gets changes from the remote repository.
git log	Shows the list of commits on the branch.
git checkout newbranch	Checks out a new branch.
git merge new-version	Merges branches into your current version.

C Programming

Command/Flag	Explanation
gcc main.c	Compiles main.c to make an executable, default name is a.out .
gcc main.c -o name	Compiles main.c to make an executable with the given name.
gcc -E main.c -o main.i	Preprocessess main.c to main.i .
gcc -S main.c -o main.s	Compiles main.c to assembly instructions in main.s .
gcc -c main.c -o main.o	Assembles main.c into machine code, creating an object file, main.o .
gcc main.o -o main.out	Links the object file main.o into an executable.
-Wall	Flag used to show major warnings when compiling.
-Wextra	Flag used to show minor warnings when compiling.
-std=c99	Flag used to specify the C99 standards.
-pedantic	Flag that is picky about syntax in source files.
valgrind --leak-check=full ./program	Runs valgrind to analyze memory usage, good for finding memory leaks.

C++ Programming

Command/Flag	Explanation
g++ main.cpp	Compiles main.cpp to make an executable, default name is a.out .
g++ main.cpp -o main.out	Compiles main.cpp to make an executable named main.out .
g++ -E main.cpp -o main.i	Preprocesses main.c to main.i .
g++ -S main.cpp -o main.s	Compiles main.c to assembly instructions in main.s .
g++ -c main.cpp -o main.o	Assembles main.cpp into machine code, creating an object file, main.o .
g++ main.o -o main.out	Links the object file main.o into an executable.

Java Programming

Command/Flag	Explanation
javac file.java	Compiles file.java to file.class .
java file	Runs file.class through the jvm.
javac -sourcepath src src/file.java -d out	Compiles file.java in the src directory into file.class in the out directory.
java -cp out file	Runs file.class, which is in the out/ directory, through the jvm.
jar cvfm MyJarFile.jar Manifest.txt *.class	Makes a .jar executable file which combines all the .class files in the directory.
jar xvf MyJarFile.jar	Expands the jar file to all the individual files it contained.
java -jar MyJarFile.jar	Runs the .jar executable using the jvm.

Gradle Commands

Command/Flag	Explanation
<gradle> is equivalent to <./gradlew> and <gradlew.bat>	If gradle is installed you may use the command "gradle", if not use "./gradlew" on Linux and OSX or "gradlew" to run the gradlew.bat file on Windows.
gradle build	Compiles the .java files into .class files, creates a .jar if enabled, and runs all junit tests that are written.
gradle classes	Compiles the .java files into .class files.
gradle clean	Removes .class, .jar, and any build files that can be re-generated.
gradle run	Compiles the java files and runs the program.
gradle test	Runs the unit tests for the project.

Python Programming

Command/Flag	Explanation
python file.py	Runs file.py using the default version of python.
python2 file.py	Runs file.py using the version of python 2 installed.
python3 file.py	Runs file.py using the version of python 3 installed.
pip install [package-name]	Installs a python package using pip.

Miscellaneous

Command/Flag	Explanation
unzip file.zip	Extracts the zip file in the current directory.
zip new.zip file1 file2 directory1	Creates a zip file by compressing all the files and directories named.
tar -cvf file.tar file1 file2 file3	Creates a tarball of the 3 files.
tar -xvf file.tar	Expands the tarball in the current directory.
tar -zcvf archive.tar.gz directory	Creates a compressed tarball of the directory specified.
tar -zxvf archive.tar.gz	Extracts and expands the compressed tarball.
sh script.sh	Runs the shell script in the terminal.
wc -w filename	Counts the number of words in a file.
wc -l filename	Counts the number of lines in a file.
ln -s target-file-path link-name	Creates a symlink to a file.
du -sh directory/*	Displays the disk space used by all the files and sub-directories of the file/directory specified.
top	Displays information about CPU and memory usage.
free	Displays information about used and unused memory in kilobytes.
free -m	Displays information about used and unused memory in megabytes.
free -g	Displays information about used and unused memory in gigabytes.
watch free	Displays information about used and unused memory and updates the display every two seconds.
sensible-browser	Opens a new window in the default web browser.
sensible-browser filename.html	Opens the local html file in a new tab in the default web browser.
time some-command	Runs a command and displays the time it took to run.