7.0 Commands

7.1 Control Characters

On most computer systems, typing an alphanumeric key while holding down the Control key will produce a new keystroke, called a control character. Control characters are often given special functions, since they can be entered while all alphanumeric keys are being interpreted by a running utility. In this document, control characters are represented by c^X, where X may be any alphanumeric key. For example, if you see c^C, you should hold down the Control key while pressing the "c" key. Some of the functions that control characters represent are system interrupts (which must be interpreted by the operating system despite any applications or programs that are running) and special input/output characters beyond the standard keyboard range (e.g., a character that causes a terminal to beep when it is printed, but that cannot be seen as a character during output). Some of the more important control characters to remember are c^C, which quits most programs, and c^Z, which susupends operation of the program until you reactivate it.

7.2 General Commands

Previous sections of this document have given simple command examples to illustrate the formats that a command may take, and some sections have described several file-handling commands in depth. The following is a list of several general-purpose UNIX commands. Most are used without flags or arguments (for instructions on issuing commands, see Section 1.3, "Typing Commands").
This will terminate the current login session, similar to the logout command (see Section 1.4, "Logging Out"). Its behavior differs slightly when exiting from remote or secondary shells. For more information about exit, read the man page. (See Section 8.0, "Getting Help.")
Clears the terminal screen. It is occasionally useful to reset the terminal, or to determine if the terminal type is set correctly. (See the man page for stty.)
Used to identify a file type. Typing file filename and pressing RETURN will tell whether a file is ASCII text, a command, a C program, a shell script, etc. The file program has some bugs and does not always yield correct results.
Used by typing login loginName. This will open a new login session (see Section 1.2, "Logging In") for the user loginName on the current computer system. The previous session (from which the login command was called) will close automatically when the new session (in the account loginName) is exited.
users, w, or who
These commands list the users of the current computer system in various formats (similar to the finger command). For descriptions of their differences, read the appropriate on-line manual pages.
Used to find the account name that the current session is using. It is useful when making use of several different accounts.
For a comprehensive list of UNIX commands, see the handout UNIX Commands.

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