资料来源 : pyDict

环境变量

资料来源 : Free On-Line Dictionary of Computing

environment variable
     
         A {variable} that is bound in
        the current environment.  When evaluating an expression in
        some environment, the evaluation of a variable consists of
        looking up its name in the environment and substituting its
        value.
     
        Most programming languages have some concept of an environment
        but in {Unix} {shell scripts} it has a specific meaning
        slightly different from other contexts.  In shell scripts,
        environment variables are one kind of {shell variable}.  They
        differ from {local variables} and {command line arguments} in
        that they are inheritted by a {child process}.  Examples are
        the PATH variable that tells the shell the {file system}
        {paths} to search to find command {executables} and the TZ
        variable which contains the local time zone.  The variable
        called "SHELL" specifies the type of shell being used.
     
        These variables are used by commands or {shell scripts} to
        discover things about the environment they are operating in.
        Environment variables can be changed or created by the {user}
        or a program.
     
        To see a list of environment variables type "setenv" at the
        {csh} or {tcsh} {prompt} or "set" at the {sh}, {bash}, {jsh}
        or {ksh} prompt.
     
        In other programming languages, e.g. {functional programming}
        languages, the environment is extended with new bindings when
        a {function}'s {parameters} are bound to its {actual
        arguments} or when new variables are declared.  In a
        {block-structured} {procedural} language, the environment
        usually consists of a {linked list} of {activation records}.
     
        (1999-01-26)