UNIX Command Conventions


  • When you log in, UNIX starts a command interpreter for you, usually called a shell.
  • The shell is what prints the command prompt and reads what you type.
  • We will cover the simplest commands now and cover more versatile ones as the tutorial progresses.
  • The simplest form of issuing a command is one command followed by any arguments it needs on a single line.
  • UNIX gives a few ways to correct typing mistakes:
    • Backspace character will erase the character before the cursor
    • Control-U (hold down the key marked Control or Ctl and press W at the same time) will erase the whole line back to the command prompt
  • You can erase a word at a time and, depending which shell you use, other much more powerful editing may be available but that will be covered later in the sections about the specific shells.
  • What keys perform the editing functions is configurable, check with your Systems Administrator if the above doesn't work.
    • Most common difference is having the Delete character for erasing characters
  • The list of UNIX commands is long. We will cover them slowly through the rest of the tutorial.
  • Most commands take flags to alter the way they work.
  • Flags usually begin with a dash ("-").
  • One or more characters immediately follows the dash.
  • Usually each character affects the command being run.
  • Each command will have its own set of flags it understands.
  • In many cases, a given flag (e.g. the f flag) will have roughly the same meaning for different commands.
  • You can get the ls command to divulge more information about each file by issuing the l flag:

    		% ls
    		% cp /etc/motd .
    		% ls
    		% ls -l
    		total 2
    		-rw-------   1 kns          1203 Mar  3 13:12 motd

  • We will cover what that means later.
  • By tradition, UNIX utilities precede their configuration file names with a "." character. By default, ls does not show files whose names begin with ".".
  • The a flag tells ls to list these files:

    % ls
    % ls -a
    .            .Xauthority  .cshrc       .netscape    .twmrc       .xsession
    ..           .Xdefaults   .login       .newsrc      .xinitrc     motd

  • Note "." and ".." directories.
  • Most commands use "--" (two consecutive dashes) to indicate the end of the flags if for some reason you need to have a command argument begin with a dash.
    • For example, suppose you managed to create a file named "-t"
    • if you type the command rm -t the rm command thinks the -t is a flag, not a filename
  • To illustrate:

    	% ls
    	-t    motd
    	% rm -t
    	rm: illegal option -- t
    	usage: rm [-fiRr] file ...
    	% ls
    	-t    motd
    	% rm -- -t
    	% ls