pwd - show the current (or "working") directory. Stands for "print working directory"
ls - show the files and folders in the working directory. I think of it as standing for "list stuff," but it's probably just short for "list."
cd - move to a directory, i.e. cd Desktop will move to the "Desktop" folder. Some special cases:
cd ..- go to the directory abovecd ~go to your "home" directory, i.e. /Users/cd(by itself) also goes to the home directorycd -go to the last directory you were in before the currentcd ../..travel two directories upcd Documents/thesis-draftsmove two directories, from the home folder to "thesis-drafts," skipping "Documents"
touch <filename> - Create an empty text file named in your current directory.
echo "Hello from the command line" - Print out any text you give it, in this case "Hello from the command line"
cat <filename> - Print the contents of a file to the screen, in this case the contents of <filename>
> - Redirects printed output to a text file, as in echo "this is some text" > hello.txt
rev - Reverses the text you give it, i.e. echo "Hello there" | rev
| - Pipe symbol. Takes output from one command and uses it as input for another command.
less <filename> - Print out the contents of a file in a paginated form. Use <Control-v> and <Alt-v> (or <Command-v and <Option-v>) to move up and down. Press q to quit.
head <filename> - Print the first section of a file
tail <filename> - Print the last section of a file
wc -l - Takes input and returns the number of lines in that input, as in cat <filename> | wc -l
uniq - Remove duplicate lines from input, as in cat <filename> | uniq. To show the duplicate files, use uniq -d.
mv - Move or rename a file. For example, mv file1 file2 will rename file to file2. You can also specify another destination, so that mv file1 ~ will move file1 to the home folder without renaming it.
Also check out other useful commands