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Diffstat (limited to 'man/man3/getenv.3')
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diff --git a/man/man3/getenv.3 b/man/man3/getenv.3 new file mode 100644 index 000000000..65bc3c81e --- /dev/null +++ b/man/man3/getenv.3 @@ -0,0 +1,141 @@ +'\" t +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" and Copyright (C) 2007, 2012 Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" References consulted: +.\" Linux libc source code +.\" Lewine's "POSIX Programmer's Guide" (O'Reilly & Associates, 1991) +.\" 386BSD man pages +.\" Modified Sat Jul 24 19:30:29 1993 by Rik Faith (faith@cs.unc.edu) +.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl) +.\" +.TH getenv 3 (date) "Linux man-pages (unreleased)" +.SH NAME +getenv, secure_getenv \- get an environment variable +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <stdlib.h> +.P +.BI "char *getenv(const char *" name ); +.BI "char *secure_getenv(const char *" name ); +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR secure_getenv (): +.nf + _GNU_SOURCE +.fi +.SH DESCRIPTION +The +.BR getenv () +function searches the environment list to find the +environment variable +.IR name , +and returns a pointer to the corresponding +.I value +string. +.P +The GNU-specific +.BR secure_getenv () +function is just like +.BR getenv () +except that it returns NULL in cases where "secure execution" is required. +Secure execution is required if one of the following conditions +was true when the program run by the calling process was loaded: +.IP \[bu] 3 +the process's effective user ID did not match its real user ID or +the process's effective group ID did not match its real group ID +(typically this is the result of executing a set-user-ID or +set-group-ID program); +.IP \[bu] +the effective capability bit was set on the executable file; or +.IP \[bu] +the process has a nonempty permitted capability set. +.P +Secure execution may also be required if triggered +by some Linux security modules. +.P +The +.BR secure_getenv () +function is intended for use in general-purpose libraries +to avoid vulnerabilities that could occur if +set-user-ID or set-group-ID programs accidentally +trusted the environment. +.SH RETURN VALUE +The +.BR getenv () +function returns a pointer to the value in the +environment, or NULL if there is no match. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR getenv (), +.BR secure_getenv () +T} Thread safety MT-Safe env +.TE +.SH STANDARDS +.TP +.BR getenv () +C11, POSIX.1-2008. +.TP +.BR secure_getenv () +GNU. +.SH HISTORY +.TP +.BR getenv () +POSIX.1-2001, C89, C99, SVr4, 4.3BSD. +.TP +.BR secure_getenv () +glibc 2.17. +.SH NOTES +The strings in the environment list are of the form \fIname=value\fP. +.P +As typically implemented, +.BR getenv () +returns a pointer to a string within the environment list. +The caller must take care not to modify this string, +since that would change the environment of the process. +.P +The implementation of +.BR getenv () +is not required to be reentrant. +The string pointed to by the return value of +.BR getenv () +may be statically allocated, +and can be modified by a subsequent call to +.BR getenv (), +.BR putenv (3), +.BR setenv (3), +or +.BR unsetenv (3). +.P +The "secure execution" mode of +.BR secure_getenv () +is controlled by the +.B AT_SECURE +flag contained in the auxiliary vector passed from the kernel to user space. +.SH SEE ALSO +.BR clearenv (3), +.BR getauxval (3), +.BR putenv (3), +.BR setenv (3), +.BR unsetenv (3), +.BR capabilities (7), +.BR environ (7) |