Begining Linux Programing Chapter 1,2

1,Static Library

Use the ar program to create the archive and add your object files to it.

If you use an archive contain two functions,but there is one function in your program,then the program will just use one function.

2,Share Library

A additional advantage is the share library can be updated independently.When Linux starts an application, it can take into account the version of a library required by the

application to prevent major new versions of a library from breaking older applications.

3.Function

There are no forward declarations in the shell.

When a function is invoked ,the positional parameters to the script,$*,$@,$#,$1,$2,and so on,are replaced by the parameters to the function.

When the function finishes,they are restored to their previous values.

The function pass the rest of the line as parameters to the function.

break:

To escape from an enclosing for,while,ro until loop.

:

1,being the alias for true.

.

you can use it to incorporate variable and function definitions into a script.

eval:

a bit like an extra $: It gives you the value of the value of a variable.

exec:

1.To replace the current shell with a different program.

2.To modify the current file descriptors.

set:

The set command sets the parameter variables for  the shell.It can be a useful way of using fields in commands that output space-separated values.

shift:

The shift command moves all the parameter variables down by one.

unset:

The unset command removes variables or functions from the environment.