UNIX & OS X COMMANDS REFERENCE

UNIX Getting Started Manual

File Management Commands

cat

Join files or display them
Read one or more files and print them on the screen (or standard output).
You can then use the > operator to combine several files into a new filee.

Examples:

cat hello.txt	Displays the file hello.txt
cat hello.txt world.txt > helloworld.txt	Combines files hello.txt and world.txt into one file called helloworld.txt

Change working directory

Examples:

cd	Changes working directory to user's home directory.
cd dir1	Changes working directory to dir1.
cd ..	Changes working directory one level up.

chmod

Change access modes on files
Only the owner of a file or a priviledged user may change its mode.
Syntax: chmod [option] mode files
Options: -R Recursively descend through directory setting modes to files
Mode: Composed of who, opcode and permission.

Who	u	User
	g	Group
	o	Other
	a	All (default)
Opcode	+	Add permission
	-	Remove permission
	=	Assign permission (and remove permission of the unspecified fields)

Permission	r	Read	OR*	4	Read
	w	Write		2	Write
	x	Execute		1	Execute

*Permissions may also be specified by a 3 digit sequence. The first digit designates owner permission; the second, group permission; and the third, others permission. Permissions are calculated by adding the values in the table.

Examples:

chmod u+x file	Adds execute-by-user permission to file
chmod 571 file	Both these examples assign read-write-execute permission by owner (7), read-write permission by group (5), and execute-only permission by others (1) to file.
chmod u=rwx, g=rx, o=x file

Copy files
Syntax: cp [options] file1 file2
cp [options] files directory

Examples

cp file1 file2	Copies file1 into file2.
cp file1 file2 file3 dir1	Copies file1, file2, and file3 to directory dir1, preserving the files' names.
cp -r dir1 dir2	Recursive copy directory dir1, its files and subdirectories to a destination directory dir2 (duplicating the tree structure).

head

Show the first few lines of a file

Examples:

head -20	Displays the first 20 lines of file1
file1

List of files or directories
Syntax ls [options][names]
If no names are given, list the files into the current directory. With one or more names, list files contained in a directory name or that match a file name.

Some Options:

-a	List all files, including the normally hidden files
-c	List files by creation/modification time
-l	Long format listing (includes permissions, owner, size, modification time, etc.)

mkdir

Create a directory
Syntax: ls [options][names]
If no names are given, list the files in the current directory. With one or more names, list files contained in a directory name or that match a file name.

Some Options:

mkdir dir1	Creates a directory named dir1.
mkdir dir1 dir2 dir3	Creates directories named dir1, dir2 and dir3.

Display files by screenful
Syntax: more file
Display the named files on a terminal, one screenful at a time. After each screen is displayed, press RETURN to display the next line or press the spacebar to display the next screenful.

pwd

Print your working directory

Remove files

rmdir

Remove directories

tail

Show the last few lines of a file

Count lines, words, and characters

Miscellaneous Commands

Precision calculator
Input can be taken from files or read from the standard input. To exit, type "quite" or "EOF".
For more information type "man bc".

cal

Display calendar
With no arguments, cal prints the calendar for the current month. Otherwise, print either a 12-month calendar (beginning with January) for the given year or a one-month calendar of the given month and year.

Examples:

cal 10 2003	Displays one-month calendar for October, 2003.
cal 2005	Displays 12-month calendar for 2005

clear

Clear the screen

man

Display information form the on-line reference manuals.
Syntax: man[command]

Example:

man mkdir

Display manual pages from command "mkdir".

tar

Tape archiver
Syntax: tar[options][files] Copy files to or restore files from tape. If any files are directories, tar acts on the entire subtree.

Options	-zcvf arch	Create a new tape arch.
	-ztvf arch	Print names of files in arch.
	-zrvf arch	Append files to tape arch.
	-zxvf arch	Extract files tape arch.

Visual text editor
Syntax: vi [file] If file exists, open file for editing. Otherwise, create file and open for editing. If no file is specified, vi opens with an empty buffer.

Some vi commands:

a	Append afer the cursor.
A	Append at end of line.
i	Insert before cursor.
I	Insert at beginning of line.
o	Open a line below current line.
O	Open a line above current line.
dd	Delete current line.
:w	Write to file. (use :w! to force write)
:q	Quit vi. (use :q! to force quit)
h	Move one character to the left.
j	Move one line down
k	Move one line up.
l	Move one character to the right.

System Status Commands

chgrp

Change file group
Syntax: chgrp [options] newgroup files
Change the ownership of one or more files to newgroup. You must own the file or be a priviledged user to succeed this command.

Example:

chgrp hello.txt group1	Changes the group for file hello.txt to group1
chgrp -R dir1 group1	Recursively descends through directory dir1, including subdirectories, setting group to group1

chown

Change file owner
Syntax: chown [options] newowner files
Change the ownership of one or more files to newowner.

Example:

chown user1 file1 file2	Changes the owner of file1 and file2 to user1.
chown -R user1 dir1	Recursively descends through directory dir1, including subdirectories, setting the owner to user1.

date

Display the current date and time. Priviledged users may also set a date and time.

finger

Point out information about users.
Syntax: finger [options] users
Displays data about one or more users.

hostname

Print the name of the host machine.

Report on active process
Syntax: ps [options]

Options	-A	List all processes.
Options	-u users	List processes only for usernames in users.

For more options type man ps.

who

List the names of users currently logged into the system.

whoami

Print the effective username.