Manpages - export.1p

This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

export — set the export attribute for variables

  export name[=word]...
  export -p

The shell shall give the export attribute to the variables corresponding to the specified /name/s, 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 POSIX.1‐2017, 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:

1.

Read-only variables with values cannot be reset.

2.

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.

See the DESCRIPTION.

See the DESCRIPTION.

Not used.

None.

None.

Default.

See the DESCRIPTION.

The standard error shall be used only for diagnostic messages.

None.

None.

 0

All name operands were successfully exported.

>0

At least one name could not be exported, or the -p option was specified and an error occurred.

Default.

The following sections are informative.

Note that, unless X was previously marked readonly, the value of “$?” after:

    export X=$(false)

will be 0 (because export successfully set X to the empty string) and that execution continues, even if set -e is in effect. In order to detect command substitution failures, a user must separate the assignment from the export, as in:

    X=$(false)
    export X

Export PWD and HOME variables:

    export PWD HOME

Set and export the PATH variable:

    export PATH=/local/bin:$PATH

Save and restore all exported variables:

    export -p > temp-file
    unset a lot of variables
    ... processing
    . temp-file

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 dot script.

None.

Section 2.14, Special Built-In Utilities

The Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology – Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

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