General Commands

General Commands

These commands are good to keep in mind when doing any sort of work on a UNIX computer.

^C

Usually kills whatever you are doing and signals the shell to accept the next command. Use ^C only if you are stuck, since work you did during the killed command may be lost.

^Z

Usually typed by accident, this control code temporarily suspends a command, whereupon the shell can accept the next command. Use fg (foreground) to get the suspended process running again; type jobs to see if you have any suspended or background processes. Do not use ^Z unless you really intend to, particularly when editing files or reading mail, since you can easily get inconsistent versions or lose mail if you execute the command a second time without finishing the first one.

crypt input output

Encrypt or decrypt a file (it knows which way to go). It will ask you for a key. The algorithm is not sufficiently strong for national security issues.

date

Displays the current date and time.

finger name

Looks up the loginID of name.

e.g. finger Gilfong will give you the loginID (and full name) of everyone named Gilfong. Be prepared for a lot of output with common names. You can also specify the loginID to find the person's full name.

gunzip file

The inverse of gzip: restores the original file.

gzip file

Compresses file. The full-size file is removed and the compressed file has the same name with an extension of ".gz" added. You can get 4 to 1 compression on low-entropy data.

hostname

Gives the name of the computer on which you are currently working.

kill pid

Cancel the process with identification pid

pkill process

Cancel the named process - e.g. pkill firefox-bin will kill your firefox session. This is useful as firefox often refuses to die and you will not be able to start up a new session without killing the old one.

logout

Ends your session. NOTE: you must logout every time you are finished at the terminal or other userss will be able to change your files. On office machines please do not leave idle sessions active overnight, both because of the security hazard and because the unused programs use up system resources. An alternative command is exit.

lpr filename

Prints filename to the default printer. You can change your default printer by typing setenv PRINTER N, where N is the number of the desired floor. To print filename to floor N, type lpr -PN filename. Save trees by viewing documents onscreen, and mind your paper quota.

lprm pid

Cancels the print job pid.

Also, lprm -PN pid cancels job pid on floor N.

lpq

Checks on status of print jobs on your default printer. lpq -PNchecks print jobs on printer N. lprm -PN jobid will remove jobid from printer N.

locate file

gives the location of file.

mail

Starts an email program that doesn't work well. Use the email program pine instead.

man command

Gives information from the UNIX manual about command.

Also, man -k word will list manual pages whose titles contain the keyword word.

nice -prior job

Gives job job processing priority value prior (1 being the highest priority level and 19 the lowest) which tells the computer how to process tasks.

e.g. nice -19 ./a.out & runs the program a.out in the background at the lowest priority.

passwd

Changes your password. You will be asked to type the old password first, and then the new password twice. None of this is visible on the screen.

command1 | command2

Called the “pipe” command. Takes the output of command command1 and uses it as the input for command2.

e.g. ls | lpr prints the names of the files listed in the cuurent directory.

uptime

Shows the load on the computer you are currently using.

who

Lists all users on the computer in which you are currently working.

whoami

Tells who is currently logged on a specific terminal