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putenv(3p) — Linux manual page

PUTENV(3P)              POSIX Programmer's ManualPUTENV(3P)

PROLOG        top

       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.

NAME        top

       putenv — change or add a value to an environment

SYNOPSIS        top

       #include <stdlib.h>       int putenv(char *string);

DESCRIPTION        top

       Theputenv() function shall use thestring argument to set       environment variable values. Thestring argument should point to a       string of the form "name=value".  Theputenv() function shall make       the value of the environment variablename equal tovalue by       altering an existing variable or creating a new one. In either       case, the string pointed to bystring shall become part of the       environment, so altering the string shall change the environment.       Theputenv() function need not be thread-safe.

RETURN VALUE        top

       Upon successful completion,putenv() shall return 0; otherwise, it       shall return a non-zero value and seterrno to indicate the error.

ERRORS        top

       Theputenv() function may fail if:ENOMEMInsufficient memory was available.The following sections are informative.

EXAMPLES        top

Changing the Value of an Environment Variable       The following example changes the value of theHOME environment       variable to the value/usr/home.           #include <stdlib.h>           ...           static char *var = "HOME=/usr/home";           int ret;           ret = putenv(var);

APPLICATION USAGE        top

       Theputenv() function manipulates the environment pointed to byenviron, and can be used in conjunction withgetenv().       Seeexec() for restrictions on changing the environment in multi-       threaded applications.       This routine may usemalloc() to enlarge the environment.       A potential error is to callputenv() with an automatic variable       as the argument, then return from the calling function whilestring is still part of the environment.       Although the space used bystring is no longer used once a new       string which definesname is passed toputenv(), if any thread in       the application has usedgetenv() to retrieve a pointer to this       variable, it should not be freed by callingfree().  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 toputenv() for the same       variable.       Thesetenv() function is preferred over this function. One reason       is thatputenv() is optional and therefore less portable. Another       is that usingputenv() can slow down environment searches, as       explained in the RATIONALE section forgetenv(3p).

RATIONALE        top

       Refer to the RATIONALE section insetenv(3p).

FUTURE DIRECTIONS        top

       None.

SEE ALSO        top

exec(1p),free(3p),getenv(3p),malloc(3p),setenv(3p)       The Base Definitions volume of POSIX.1‐2017,stdlib.h(0p)

COPYRIGHT        top

       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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017PUTENV(3P)

Pages that refer to this page:stdlib.h(0p), exec(3p), getenv(3p), setenv(3p)

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