174 lines
4.3 KiB
Groff
174 lines
4.3 KiB
Groff
.\" Copyright (c) 1988, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getenv.3 8.2 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd October 12, 2006
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.Dt GETENV 3
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.Os
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.Sh NAME
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.Nm getenv ,
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.Nm putenv ,
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.Nm setenv ,
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.Nm unsetenv
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.Nd environment variable functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft char *
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.Fn getenv "const char *name"
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.Ft int
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.Fn setenv "const char *name" "const char *value" "int overwrite"
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.Ft int
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.Fn putenv "const char *string"
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.Ft void
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.Fn unsetenv "const char *name"
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.Sh DESCRIPTION
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These functions set, unset and fetch environment variables from the
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host
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.Em environment list .
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For compatibility with differing environment conventions,
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the given arguments
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.Fa name
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and
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.Fa value
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may be appended and prepended,
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respectively,
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with an equal sign
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.Dq Li \&= .
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.Pp
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The
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.Fn getenv
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function obtains the current value of the environment variable,
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.Fa name .
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The application should not modify the string pointed
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to by the
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.Fn getenv
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function.
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.Pp
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The
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.Fn setenv
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function inserts or resets the environment variable
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.Fa name
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in the current environment list.
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If the variable
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.Fa name
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does not exist in the list,
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it is inserted with the given
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.Fa value .
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If the variable does exist, the argument
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.Fa overwrite
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is tested; if
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.Fa overwrite
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is zero, the
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variable is not reset, otherwise it is reset
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to the given
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.Fa value .
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.Pp
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The
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.Fn putenv
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function takes an argument of the form ``name=value'' and is
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equivalent to:
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.Bd -literal -offset indent
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setenv(name, value, 1);
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.Ed
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.Pp
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The
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.Fn unsetenv
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function
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deletes all instances of the variable name pointed to by
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.Fa name
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from the list.
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.Sh RETURN VALUES
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The
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.Fn getenv
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function returns the value of the environment variable as a
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.Dv NUL Ns
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-terminated string.
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If the variable
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.Fa name
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is not in the current environment,
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.Dv NULL
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is returned.
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.Pp
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.Rv -std setenv putenv
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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The function
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.Fn setenv
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or
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.Fn putenv
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failed because they were unable to allocate memory for the environment.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr sh 1 ,
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.Xr execve 2 ,
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.Xr environ 7
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.Sh STANDARDS
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The
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.Fn getenv
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function conforms to
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.St -isoC .
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.Sh HISTORY
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The functions
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.Fn setenv
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and
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.Fn unsetenv
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appeared in
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.At v7 .
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The
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.Fn putenv
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function appeared in
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.Bx 4.3 Reno .
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.Sh BUGS
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Successive calls to
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.Fn setenv
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or
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.Fn putenv
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assigning a differently sized
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.Fa value
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to the same
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.Fa name
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will result in a memory leak.
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The
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.Fx
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semantics for these functions
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(namely, that the contents of
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.Fa value
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are copied and that old values remain accessible indefinitely) make this
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bug unavoidable.
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Future versions may eliminate one or both of these
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semantic guarantees in order to fix the bug.
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