1.10 Help

A feature in bash that no other shell has is an online help system. The help command gives information on commands in bash . If you type help by itself, you'll get a list of the built-in shell commands along with their options.

If you provide help with a shell command name it will give you a detailed description of the command:

$ help cd
cd: cd [-PL] [dir]
 Change the current directory to DIR. The variable $HOME is the
 default DIR. The variable $CDPATH defines the search path for
 the directory containing DIR. Alternative directory names in
 CDPATH are separated by a colon (:). A null directory name is
 the same as the current directory, i.e. `.'. If DIR begins with
 a slash (/), then $CDPATH is not used. If the directory is not
 found, and the shell option `cdable_vars' is set, then try the
 word as a variable name. If that variable has a value, then cd
 to the value of that variable. The -P option says to use the
 physical directory structure instead of following symbolic links;
 the -L option forces symbolic links to be followed.

You can also provide help with a partial name, in which case it will return details on all commands matching the partial name. For example, help re will provide details on read , readonly , and return . The partial name can also include wildcards. You'll need to quote the name to ensure that the wildcard is not expanded to a filename. So the last example is equivalent to help ' re* ' , and help ' re?? ' will only return details on read .

Sometimes help will show more than a screenful of information and it will scroll the screen. You can use the more command to show one screenful at a time by typing help command | more.


Learning the Bash Shell
Learning the bash Shell: Unix Shell Programming (In a Nutshell (OReilly))
ISBN: 0596009658
EAN: 2147483647
Year: 1998
Pages: 104

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