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(libc.info)Environment Variables

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Environment Variables
=====================

   When a program is executed, it receives information about the
context in which it was invoked in two ways.  The first mechanism uses
the ARGV and ARGC arguments to its `main' function, and is discussed in
Note: Program Arguments.  The second mechanism uses "environment
variables" and is discussed in this section.

   The ARGV mechanism is typically used to pass command-line arguments
specific to the particular program being invoked.  The environment, on
the other hand, keeps track of information that is shared by many
programs, changes infrequently, and that is less frequently used.

   The environment variables discussed in this section are the same
environment variables that you set using assignments and the `export'
command in the shell.  Programs executed from the shell inherit all of
the environment variables from the shell.

   Standard environment variables are used for information about the
user's home directory, terminal type, current locale, and so on; you
can define additional variables for other purposes.  The set of all
environment variables that have values is collectively known as the
"environment".

   Names of environment variables are case-sensitive and must not
contain the character `='.  System-defined environment variables are
invariably uppercase.

   The values of environment variables can be anything that can be
represented as a string.  A value must not contain an embedded null
character, since this is assumed to terminate the string.

Environment Access

How to get and set the values of

environment variables.

Standard Environment

These environment variables have

standard interpretations.