Basic Unix Commands

Basic Unix commands

COMMAND	COMMENTS
`cat filename`	Copies the named file (or files) to the output.
`cd`	Changes your working directory to be your login directory.
`cd ..`	Change directories by moving up one level.
`cd dir_name`	Changes directory to the directory named.
`chmod u+rwx filename`	Changes the protection on a file. u = user (the file owner), +rwx = "on" for read, write, and execute. Also can use - for "off", e.g., go-x means "off" for "group" and "other" (i.e., everyone else).
`clear`	Clears the terminal screen.
`cp filename1 filename2`	Copies file filename1 to filename2.
`date`	Displays date and time.
`diff filename1 filename2`	Compares file filename1 to filename2.
`echo anything`	Simply write the arguments to the standard output.
`emacs filename`	Edits the named file using the emacs editor.
`exit`	Exit from the current shell. (If this is your login shell, it will log you out.)
`grep pattern filename`	Displays lines from the named file which match the pattern.
`head filename`	Look at the start of the named file. Also head -20 for first 20 lines (etc.)
`kill process_id`	Kill one of your processes. If it doesn't work, use `kill -9 process_id`
`less filename`	Displays file, one page at a time, with prompting.
`lp filename`	Prints the named file.
`ls`	Brief listing of your files (brief).
`ls -a`	Gives listing that includes files starting with a "dot".
`ls -al`	Gives detailed listing of your files.
`man command_name`	Find out more about the command specified.
`mkdir dir_name`	Create (make) a subdirectory named dir_name.
`mv filename1 filename2`	Renames file fname1 to fname2 (also moves file, if directory path is included).
`ps -x`	Show what processes you are running.
`rm filename`	Deletes the specified file.
`rmdir dir_name`	Removes (deletes) the specified subdirectory (which must be empty).
`tail filename`	Look at the end of the named file. Also tail -20 for last 20 lines (etc.)
`tin newsgroup`	Read a newsgroup.
`vi filename`	Edit the named file using the vi editor. [Also see emacs (above).] Emergency exit: type ESCAPE then :q!

Other basic Unix things

All Unix processes have three i/o streams by default:

stdin (standard input) is the main source of input to the process. By default it corresponds to your keyboard.
stdout (standard output) is the main destination of normal output. By default it corresponds to the window the process is running in.
stderr (standard error) is the main destination of error messages. By default it corresponds to the window the process is running in.

The default assignment of the three streams can be changed when the process is run:

program <infile >outfile
This runs the program with stdin assigned to the file infile and stdout assigned to the file outfile. stderr is still assigned to your window (so you will still see error messages).
program <infile >&outfile
This runs the program with stdin assigned to the file infile and both stdout and stderr assigned to the file outfile. In this case, normal output and error messages will appear mixed together in the output file.
>> and >>& are like > and >& except that they append to the output instead of overwriting it.
program1 | program2
This construct is called a pipe. Both programs are run, with the standard output of program1 connected to the standard input of program2. Any number of programs can be connected together in this way.

When specifying filenames, some wildcards are permitted:

A question mark "?" matches any single character.
An asterisk "*" matchs zero or more characters.
A set of characters in square brackets "[ ]" matches a single character that is in the set. The set can include ranges of characters, such as a-z.
A list of things in curly braces "{ }" matches any of the things in the list. (This is not available in all Unix shells.)
A tilde and slash "~/" at the start of a filename matches the name of your home directory.

Examples:
joe? matches joe0 and joex but not joe or joe37.
jane*.html matches jane.html or jane-b.html.
s[oui]n matches only son, sun or sin.
mark[0-9].txt matches mark3.txt but not mark37.txt or markb.txt.
~/*.{htm,html} matches anything in your home directory that ends with .htm or .html.