Linux environment variable operations

Linux environment variable operations-general Linux technology-Linux programming and kernel information. The following is a detailed description. The main environment variables include the PATH system PATH, the HOME system root directory, and the number of records that History commands are stored in HISTSIZE. LOGNAME: HOSTNAME: The Host Name of the current user logon. SHELL: The SHELL name used by the current host, LANG/LANGUAGE environment variable, MAIL directory

Command: echo $ PATH

Export welcome = "hh :"

Env show all, env | grep welcome found

Set displays all locally defined

Unset $ welcome Delete Environment Variables

Readonly $ welcome cannot be modified or deleted.

You can use C to access environment variables: several functions are used:

Getenv () is used to access an environment variable. The input parameter is the name of the variable to be accessed, and the return value is a string. If the accessed environment variable does not exist, NULL is returned.

Setenv () is a function used to set an environment variable in a program.

Unsetenv () is a function used to clear a specific environment variable.

In addition, the pointer variable environ points to a list containing all environment variables. The following program can print all the environment variables in the current running environment:

# I nclude
Extern char ** environ;
Int main ()
{
Char ** var;
For (var = environ; * var! = NULL; ++ var)
Printf ("% s \ n", * var );
Return 0;
}