UNIX and OS X Commands Reference

Some Very Cool Unix Commands that might be real helpful for an interview or for anything while working with Unix or OS X.

cd (change directory)
cd myfolder	Changes the current working directory to “myfolder”
cd ..	Go up one level to the current working directory.
cd ../..	Go up two levels to the current working directory.
cd /	Changes the current working directory to the root directory.
cd ~	Changes the current working directory to your home directory.

mkdir (Make directory)
mkdir freshershome	Create a new folder called “freshershome” in the current directory.
mkdir /freshershome	Create a new folder called “freshershome” in the root directory.
mkdir ~/freshershome	Create a new folder called “freshershome” in your home directory.

ls (list)
ls	list the file names in the current working directory.
ls -l	list the file names with “long” description/information (size, privilages, etc)
ls -a	list “all” file names in the current working directory including the hidden files.
ls -l *.jpg	list the file names ending in “.jpg” and display it in “long” description format(-l)

cp (copy)
cp letter.txt newletter.txt	Copy the file called “letter.txt” and name it “newletter.txt” in the current directory
cp my.cnf /etc/my.cnf	Copy the file “my.cnf” and put it inside the root -> etc folder.
cp tax05.db ~/Taxes	Copy the file name “tax05.db” and put it inside my home directory -> Taxes folder
cp “.jpg ~/freshershome	Copy all the files with “.jpg” extention and put them inside my home directory -> freshershome folder
cp -R ~/Docs /backups/’Docs Backup’	Copy the entire “Docs” directory from my home page and put it inside the root -> backups and call it “Docs backup” (use quotes if you use folder names with space. example: ‘Docs Backup’ (-R stands for “Recursive”)
sudo cp -Rp /Users /UsersBackup	Copy the entire “Users” folder including subfolders and files, preserve owner, group, permissions, and timestamps and save the new folder in the root -> UsersBackup location. “-Rp” stands for Recursive Preserve: Recursive: Copy include subfolders and files. Preserve: Preserve owner, group, permissions, and timestamps information. (use “sudo” to get root access temporarily.)

mv (Move or Rename)
mv /letter.txt ~/letter.txt	Move the file “letter.txt” from the root directory to the home directory.
mv badletter.txt niceletter.txt	Rename the file “badletter.txt” to “niceletter.txt” in the current directory.
mv Pictures freshershome	Rename the folder “Pictures” to “freshershome” in the current directory.
mv *.jpg ~/freshershome	Move all the files with “.jpg” extention and put them inside my home directory -> freshershome folder

rm (Remove)
rm letter.txt	Delete the file “letter.txt” from the current directory.
rm ~/Badfreshershome/*.jpg	Delete all the files with the ‘.jpg’ extention inside your home directory -> “Badfreshershome” folder.
rm -R Temp	Delete the “Temp” directory and all of its contents in the current directory (-R stands for “Recursive”)
rm -fr Temp	Delete the “Temp” directory and all of its contents including write-protected files without prompting in the current directory (-f stands for “force” -r stands for “recursive”)

find (files and folders)
find ~ -name myletter.doc -print	Search for the file names “myletter.doc” inside my home directory and print the result to the screen
sudo find / -name mysql -print	Search for the file and folder names “mysql*” starting from the root directory and everywhere within it and print the result to the screen. (use “sudo” to get root access temporarily.)
find . -name myletter.doc -print	Search for the file names “myletter.doc” inside the current directory and print the result to the screen
find . -name ‘myletter*’ -print	Search for the file names starting “myletter” inside the current directory and print the result to the screen

locate (similar to find)
locate ~ -name myletter.doc	Search for the file names “myletter.doc” inside my home directory and print the result to the screen

pwd (print working directory)
pwd	Displays the pathname of the current working directory.

who (who logged in)
who	Displays who is logged into the system.
who am i	Displays my user name.
who -uH	Displays who is logged into the system including heading “H” and idle time information.

su (set user) – type exit to switch back to your own identity
su	Temporarily become the root user. (this will give you root access privilages and the most control over the OS) – it will prompt you for the administrator password.
su username	Temporarily become another user called “username” (replace “username” with the user that you wish to use as your new identity – this will give you access privilages for the “username”) – it will prompt you for the that user’s password.

sudo (set user and do . . . . . . ) – similar to su except ‘su’ will give you prompt but ‘sudo’ you can start typing commands right after the ‘sudo’ command.
sudo find / -name mysql -print	Temporarily changes your identity to the root user so you can search for all the files including the once that require root access privilage. It prompts you for administrator/root password
sudo Bobuser rm /Users/Bobuser/freshershome/myphoto.jpg	Temporarily changes your identity to the “Bobuser” identity so you can delete a photo named “myphoto.jpg” from the home directory -> freshershome folder belonging to Bobuser – It prompts you for “Bobuser”‘s password.

ps (running processes)
ps -ax	List all running processes
ps -aux	List detailed information on all running processes.

top (CPU-intensive processes currently running) – press the “q” key to quit the “top” utility
top	List all running processes sorted by process id – descending and updating every second – don’t forget to press the “q” key to quit, otherwise it will run continuously.
top -us10	List all running processes sorted by CPU usage – descending and updating every 10 seconds – don’t forget to press the “q” key to quit, otherwise it will run continuously.

kill
kill 160	Tell the process ID #160 to terminate.
kill -9 160	Terminate the process ID # 160 at once without any hesitation.