Introduction

• 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
  		motd
  		% 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
  motd
  % 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
  	motd
  	%