7.4 System Environmental Variables

In a typical operating system, several system-wide parameters are defined which tune the behaviour of the programs executed on that system. These environment variables, as they are called, can be accessed via the third argument in the main(int argc, char *argv[], char *env[]) function header. Some of the more common environment variables are:

HOSTNAME name of the computer

BASH the shell program in use

CLASSPATH a list of paths for Java classes and jar libraries

HOME the home directory of the current user

HZ the rate of basic timer interrupt

JAVA_HOME place where the Java system is stored

MANPATH  a list of paths where manual pages can be found

PS1, PS2  the primary and secondary prompt strings

TERM  the type of the Terminal in use

LD_LIBRARY_PATH  a list of paths at which various shared libraries can be found

USER  account name of the current user

UID  identification number of the current user

As you can see, a variety of information is kept in the environment variables.