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Top Forums UNIX for Dummies Questions & Answers help..Environment variables... Post 81923 by Unbeliever on Thursday 25th of August 2005 05:31:52 AM
Old 08-25-2005
1) An environment variable is simply a piece of information identified by a particular string that is available to one or more processes on the system. Environment variable names are by convention upper case, though this is not required.

For exmple the PATH environment variable contains a ':' deleimited list of directories to search in order to find any particular command.

2) No. There can be any number of environment variables on a system

3) set | more
 

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standards(5)							File Formats Manual						      standards(5)

NAME
standards - UNIX standards behavior on HP-UX DESCRIPTION
HP-UX conforms to various UNIX standards. In some cases, these standards conflict. This manpage describes the methods that programmers and users must follow to have an application conform and execute according to a particular UNIX standard. UNIX Standard Conformant Programmer Environment The following table lists feature test macros and environment variables that must be defined while compiling an application. Both a fea- ture test macro and an environment variable must be defined while compiling the application so that the application conforms and executes according to a particular UNIX standard. Otherwise, the behavior is undefined. Standard Feature Test Macros to be Environment variable defined during compilation to be set UNIX 95 _XOPEN_SOURCE_EXTENDED=1 UNIX95 or UNIX_STD=95 or UNIX_STD=1995 UNIX 2003 _XOPEN_SOURCE=600 UNIX_STD=2003 The compiler uses the feature test macros to obtain the appropriate namespace from the header files. The compiler uses the environment variable to link in an appropriate object file to the executable. Using the environment variable customizes libc to match UNIX standards for various functions. If an application has already been compiled for default HP-UX behavior or for one particular standard, and needs to change to a particular UNIX standard behavior, recompile the application as specified in the above table. For an HP-UX command to conform to a particular UNIX standard behavior, the application has to set the corresponding environment variable as specified in the above table before executing that command. UNIX Standard Conformant User Environment To enable a particular UNIX standard conformant user environment, set the corresponding environment variable as defined in the above table. EXAMPLES
The following examples shows an application example. To have the system be conformant to UNIX2003 behavior, set the environment variable to and define the feature test macro before compilation. The following example changes the command to have UNIX95 behavior by setting one of the environment variables to or to before executing that command. There are three ways of setting the environment variable for UNIX95: or or SEE ALSO
cc(1), stdsyms(5). standards(5)
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