Frequently Used Unix Commands

The Unix operating system supports many commands. To review a more complete definition of any of the commands listed below, type man command at the Unix shell prompt (%), where you have replaced command with the name of a Unix command. For example, type man exit to find out more about the exit command.

Note This document assumes you are using Unix on the ITS Login Service (host name login.itd.umich.edu). These instructions apply to many other Unix machines; however, you may notice different behavior if you are not using the ITS Login Service.

Tip The variable files refers to a list of any number of files separated by white space; in the same way; names refers to a list of file or directory names separated by white space.

General

apropos command

Locates commands by keyword lookup.

exit

Terminates your current session, or shell.

man command

Displays the Unix manual page describing a given Unix command.

File System Navigation

cd

Returns to your home directory.

cd directory

Changes directory to make directory your current directory.

file files

Determines file type.

ls

Lists the contents of the current directory.

ls names

Lists the contents of the directories; names can name files and/or directories:

ls -l

. . . in a long format, showing permissions, owner, size, and other file info.

ls -a

. . . all files, including "hidden" files (file names that begin with a dot ".").

ls -R

. . . Recursively, for all subdirectories.

ls -t

. . . in time order (when modified, newest to oldest) rather than in name order.

pwd

Displays the name of the current directory, or "print working directory."

File/Directory Manipulation

compress files

Reduces the size of a file.

uncompress files

Restores compressed files to their original form.

cp file1 file2

Copies file(s).

cp files directory

Copies file(s) into a directory.

cp -r dir1 dir2

Copies a directory and, recursively, its subdirectories.

mkdir directory

Creates, or "make" a directory.

mv file1 file2

Moves a file or, if file1 and file2 are in the same directory, rename a file.

mv files directory

Moves files into a directory.

mv dir1 dir2

If directory dir2 exists, moves dir1 into dir2; otherwise, rename dir1 as dir2.

rm files

Removes (erase) file(s).

rm -r names

Removes files, directories, and recursively, any subdirectories.

rmdir directory

Removes directory (directory must be empty).

Data Manipulation

cat files

Concatenates file(s); you can use cat to display the contents of a file (this is not advisable if the file is a binary file).

grep "pattern" files

Displays all lines in the files that match a pattern.

more files

Displays contents of files one screen at a time.

sort files

Orders the lines in a file or files alphabetically (this command does not alter the file or files -- it merely displays the sorted output to the screen):

sort -r files

. . . in reverse order.

sort -n files

. . . numerically (puts 2 before 10 instead of after).

Networking/Communications

ssh hostname

Connects to a remote host using Secure Shell.

Miscellaneous

!!

Repeats last shell command.

!string

Repeats last shell command that began with string (for example, type "!m" to repeat the last command that began with "m").

cal

Displays a calendar of the current month.

cal month year

Displays a calendar of the given month and year. Note that the year must be fully qualified, for example, "2003" and not "03."

clear

Clears terminal screen.

date

Displays the current local date and time.

who

Displays a list of users currently logged in.