The shell shall give the export attribute to the variables corresponding
to the specified names, which shall cause them to be in the environment
of subsequently executed commands. If the name of a variable is followed by =
word, then the value of that variable shall be set to word.
The export special built-in shall support the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
When -p is specified, export shall write to the standard output
the names and values of all exported variables, in the following format:
"export %s=%s\n", <name>, <value>
if name is set, and:
"export %s\n", <name>
if name is unset.
The shell shall format the output, including the proper use of quoting, so that
it is suitable for reinput to the shell as commands that achieve the same
exporting results, except:
Read-only variables with values cannot be reset.
Variables that were unset at the time they were output need
not be reset to the unset state if a value is assigned to the variable
between the time the state was saved and the time at which the saved
output is reinput to the shell.
When no arguments are given, the results are unspecified.
Some historical shells use the no-argument case as the functional equivalent of
what is required here with -p. This feature was left unspecified
because it is not historical practice in all shells, and some scripts may rely
on the now-unspecified results on their implementations. Attempts to specify
the -p output as the default case were unsuccessful in achieving
consensus. The -p option was added to allow portable access to the
values that can be saved and then later restored using; for example, a
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html