Unix 101: Basic Unix

Directories are special files that hold the names of other files or other directories. In this way, the Unix file system looks like a hierarchical tree, similar to DOS. Note that directories are separated by a forward slash ( / ) not a backslash ( \ ) as in DOS.

How much disk space are you allowed to use? See ACCC Online Disk Space Policy.

file name

A file name is a string of characters. Unix does not give special relevance to periods or other characters, although some programs expect specific types of filenames.

full path

The full path of a file specifies all directories, such as /usr/local/bin/foo.bar. The filename foo.bar can be used for this file when /usr/local/bin is the current directory.

file permissions

Each file has an associated owner and group. The owner is a logon account, and the group is a possibly empty group of logon accounts. The read, write, and execute permissions (which can be set by the owner) can be different for the owner, group, and public (other). Permissions apply to directories as well as files.

 drwx------ 2 bobg comp  512 Jun  7 09:49 mydir
 -rwxr-xr-x 1 bobg comp  321 May 30 14:36 myscript

The first character of the permissions tells what kind of "file" it is; d for directory, hyphen (-) for regular file. The remaining nine characters are three triplets. The triplets give the read, write, and execute permissions for that file or directory for that file for, respectively, the file's owner, its group owner, and for the public (other). The r (read), w (write), and x (execute), indicate the presence of read, write and execute permissions; the hyphen (-) indicates their absence. For directories: r permission allows you to list the files in the directory, w permission allows you to create or remove files from the directory, and x permission allows you to cd to the directory.

Thus, in this example, both files are owned by bobg and have the group comp as group owner. mydir is a subdirectory in which only bobg can read, write, and execute; and myscript is a file in which bobg can read, write, execute, and everyone else, including those in group comp, can read and execute but not write.

The chmod command changes file permissions. For example chmod u+x file adds execute permission to file for the owner (user); use u-x to remove execute permission for the owner. u indicates the file's owner (user), g the owner's group, o the public (other), or a for all three; and r is read permission, w is write permission, and x is execute permission.

who am i

To do the obvious; just who lists everyone who is logged on; likewise hostname tells you the name of the machine you're using.
(tigger (AIX) man page; icarus (Solaris) man page)

pwd

To display current directory

mkdir foo

To make a new directory called foo.

cd

To change to your home directory from anywhere.

cd bin

To change to the bin directory under the current directory.

cd /usr/local/bin

To change to the /usr/local/bin directory, regardless of what your current directory is; much of the public software is stored in the subdirectories of the usr directory

ls -l -a -R | more

To get a list of all files in a directory. -l to get a long listing, with permissions; -a to include files with filenames beginning with a period (.); and -R (note the R is uppercase) to also list the files in all subdirectories of the current directory. And since this is likely to be a long listing, it's "piped" into more so the display pauses at the end of each screen.

ls -l a*.c

To get a long listing of all files with filenames starting with a and ending in .c.

more .profile

To display your .profile file, when your current directory is your home directory.
(See Using Unix: Customizing Korn Shell for more information about .profile and .env files.

more ~/.profile

To display your .profile file when your current directory is not your home directory.

cp ../foobar .

To copy the file foobar from the parent of the current directory into the current directory.

rm -i ??

To remove (erase) all files in the current directory with exactly 2 characters in the filename, verifying each erase with a y or n .

mv foobar ../newdir/fubar

To rename the file foobar to fubar and place it in the directory newdir, that is a child of the parent directory of your current directory.

chmod u+x foobar

To make the file foobar executable by its owner.

chmod -R a+r *

To make all files the current directory and all files in all subdirectories (-R) readable by everyone.

man ls

To get information on the command ls and its flags.

ps -e | more

To get a list all processes piped into more; without the -e only the processes associated with your session are listed

nohup cmd < foo.in >> foo.out &

To run the command cmd, taking input from foo.in, appending output to foo.out, and run the command in the background so that you can log off and have the command continue to run. (Without the >>, nohup puts output in the file nohup.out.)

grep double *.c

To search all the C source files for the string "double".

ls -l | grep ^d | wc -l

To find the number of subdirectories in the current directory.

find ~ -name foobar -print

To search for all files named foobar in your home directory tree.

uncompress foo.Z

To uncompress the compressed file foo.Z in the current directory.
(tigger (AIX) man page; icarus (Solaris) man page)

tar -xf foo.tar

To extract the contents of the file foo.tar in the current directory.

diff foobar fubar > diffbar

To find the differences between foobar and fubar and record the differences in a file called diffbar.

pine consult@uic.edu

To send a note to consult@uic.edu; enter just: pine for a complete mail management menu.
(tigger (AIX) man page; icarus (Solaris) man page)