PUTENV(3POSIX)

💖 PUTENV(3POSIX) — the POSIX Programmer's Manual one 💖

okay bestie, this page lives in the POSIX Programmer's Manual, so quick lil heads up before we even start:

⚠️ The Linux implementation of this interface may differ (so go peek at the corresponding Linux manual page for details on Linux behavior), or honestly the interface may not even be implemented on Linux. vibe check: don't assume, go check.

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✨ PROLOG ✨

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.

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🌸 NAME 🌸

putenv — change or add a value to an environment 🫶

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🎀 SYNOPSIS 🎀

#include <stdlib.h>

int putenv(char *string);

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🦋 DESCRIPTION 🦋

So like, the putenv() function shall use the string argument to set environment variable values. The string argument should point to a string of the form "name=value". The putenv() function shall make the value of the environment variable name equal to value by altering an existing variable or creating a new one. Either way, the string pointed to by string shall become part of the environment, so altering that string shall change the environment. yes really, it's holding onto your string, it's obsessed with it 💅

The putenv() function need not be thread-safe. 😭 (so like, don't be messy with it across threads, k?)

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⭐ RETURN VALUE ⭐

Upon successful completion, putenv() shall return 0; otherwise, it shall return a non-zero value and set errno to indicate the error. slay when it's zero, not slay when it isn't 💀

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🔥 ERRORS 🔥

The putenv() function may fail if:

• ENOMEM — Insufficient memory was available. 😭 the malloc said no.

The following sections are informative.

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🌈 EXAMPLES 🌈

💜 Changing the Value of an Environment Variable 💜

The following example changes the value of the HOME environment variable to the value /usr/home. iconic behavior fr fr:

#include <stdlib.h>
...
static char *var = "HOME=/usr/home";
int ret;

ret = putenv(var);

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🍓 APPLICATION USAGE 🍓

The putenv() function manipulates the environment pointed to by environ, and can be used in conjunction with getenv(). dynamic duo energy 🫶

See exec() for restrictions on changing the environment in multi-threaded applications. (yes go read it, iykyk)

This routine may use malloc() to enlarge the environment. so like, it's not free, it's doing math behind the scenes 🧚

A potential error is to call putenv() with an automatic variable as the argument, then return from the calling function while string is still part of the environment. 🚨 do NOT do this, this is the classic oopsie, your stack memory is now haunted.

Although the space used by string is no longer used once a new string which defines name is passed to putenv(), if any thread in the application has used getenv() to retrieve a pointer to this variable, it should not be freed by calling free(). If the changed environment variable is one known by the system (such as the locale environment variables) the application should never free the buffer used by earlier calls to putenv() for the same variable. basically: hands off the free(), bestie.

The setenv() function is preferred over this function. One reason is that putenv() is optional and therefore less portable. Another is that using putenv() can slow down environment searches, as explained in the RATIONALE section for getenv(). 💅 setenv() is the main character here, ngl.

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👑 RATIONALE 👑

Refer to the RATIONALE section in setenv(). that's it, that's the whole section, go read the other one 💀

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🧚 FUTURE DIRECTIONS 🧚

None. nothing. zero. nada. the future is a blank canvas ✨

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🎀 SEE ALSO 🎀

• exec
• free()
• getenv()
• malloc()
• setenv()

The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

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📜 COPYRIGHT 📜

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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay that's the whole page bestie, we ate and left no crumbs 💅✨

this lil masterpiece came to you courtesy of IEEE/The Open Group, 2017, from the PUTENV(3POSIX) page 🫶🎀