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# 3.4 Summary of Basic Commands

This section introduces some of the most useful basic commands on a UNIX system, including those covered in the last section.

Note that options usually begin with a ```-`'', and in most cases multiple one-letter options may be combined using a single ```-`''. For example, instead of using the command `ls -l -F`, it is adequate to use `ls -lF`.

Instead of listing all of the options available for each of these commands, we'll only talk about those which are useful or important at this time. In fact, most of these commands have a large number of options (most of which you'll never use). You can use `man` to see the manual pages for each command, which list all of the available options.

Also note that many of these commands take a list of files or directories as arguments, denoted by `` ...''. For example, the `cp` command takes as arguments a list of files to copy, followed by the destination file or directory. When copying more than one file, the destination must be a directory.

`cd`
  Change the current working directory.
  Syntax: `cd`
  is the directory to change to. (```.`'' refers to the current directory, ```..`'' the parent directory.)
  Example: `cd ../foo` sets the current directory to `../foo`.

`ls`
  Displays information about the named files and directories.
  Syntax: `ls ...`
  Where through are the filenames or directories to list. Options: There are more options than you want to think about. The most commonly used are `-F` (used to display some information about the type of the file), and `-l` (gives a ``long'' listing including file size, owner, permissions, and so on. This will be covered in detail later.)
  Example: `ls -lF /home/larry` will display the contents of the directory `/home/larry`.

`cp`
  Copies file(s) to another file or directory.
  Syntax: `cp ...`
  Where through are the files to copy, and is the destination file or directory.
  Example: `cp ../frog joe` copies the file `../frog` to the file or directory `joe`.

`mv`
  Moves file(s) to another file or directory. This command does the equivalent of a copy followed by the deletion of the original. This can be used to rename files, as in the MS-DOS command `RENAME`.
  Syntax: `mv ...`
  Where through are the files to move, and is the destination file or directory.
  Example: `mv ../frog joe` moves the file `../frog` to the file or directory `joe`.

`rm`
  Deletes files. Note that when files are deleted under UNIX, they are unrecoverable (unlike MS-DOS, where you can usually ``undelete'' the file).
  Syntax: `rm ...`
  Where through are the filenames to delete.
  Options: `-i` will prompt for confirmation before deleting the file.
  Example: `rm -i /home/larry/joe /home/larry/frog` deletes the files `joe` and `frog` in `/home/larry`.

`mkdir`
  Creates new directories.
  Syntax: `mkdir ...`
  Where through are the directories to create.
  Example: `mkdir /home/larry/test` creates the directory `test` under `/home/larry`.

`rmdir`
  This command deletes empty directories. When using `rmdir`, your current working directory must not be within the directory to be deleted.
  Syntax: `rmdir ...`
  Where through are the directories to delete.
  Example: `rmdir /home/larry/papers` deletes the directory `/home/larry/papers`, if it is empty.

`man`
  Displays the manual page for the given command or resource (that is, any system utility which isn't a command, such as a library function.) Syntax: `man`
  Where is the name of the command or resource to get help on.
  Example: `man ls` gives help on the `ls` command.

`more`
  Displays the contents of the named files, one screenful at a time.
  Syntax: `more ...`
  Where through are the files to display.
  Example: `more papers/history-final` displays the file `papers/history-final`.

`cat`
  Officially used to concatenate files, `cat` is also used to display the entire contents of a file at once.
  Syntax: `cat ...`
  Where through are the files to display.
  Example: `cat letters/from-mdw` displays the file `letters/from-mdw`.

`echo`
  Simply echoes the given arguments.
  Syntax: `echo ...`
  Where through are the arguments to echo.
  Example: `echo "Hello world"` displays the string ```Hello world`''.

`grep`
  Display all of the lines in the named file(s) matching the given pattern.
  Syntax: `grep ...`
  Where is a regular expression pattern, and through are the files to search.
  Example: `grep loomer /etc/hosts` will display all lines in the file `/etc/hosts` which contain the pattern ```loomer`''.

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