stdlib/FreeBSD/getenv.3

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  36 .\"     @(#)getenv.3    8.2 (Berkeley) 12/11/93
  37 .\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.13 2002/12/18 13:33:03 ru Exp $
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  39 .Dd December 11, 1993
  40 .Dt GETENV 3
  41 .Os
  42 .Sh NAME
  43 .Nm getenv ,
  44 .Nm putenv ,
  45 .Nm setenv ,
  46 .Nm unsetenv
  47 .Nd environment variable functions
  48 .Sh LIBRARY
  49 .Lb libc
  50 .Sh SYNOPSIS
  51 .In stdlib.h
  52 .Ft char *
  53 .Fn getenv "const char *name"
  54 .Ft int
  55 .Fn setenv "const char *name" "const char *value" "int overwrite"
  56 .Ft int
  57 .Fn putenv "const char *string"
  58 .Ft void
  59 .Fn unsetenv "const char *name"
  60 .Sh DESCRIPTION
  61 These functions set, unset and fetch environment variables from the
  62 host
  63 .Em environment list .
  64 For compatibility with differing environment conventions,
  65 the given arguments
  66 .Fa name
  67 and
  68 .Fa value
  69 may be appended and prepended,
  70 respectively,
  71 with an equal sign
  72 .Dq Li \&= .
  73 .Pp
  74 The
  75 .Fn getenv
  76 function obtains the current value of the environment variable,
  77 .Fa name .
  78 If the variable
  79 .Fa name
  80 is not in the current environment,
  81 a null pointer is returned.
  82 .Pp
  83 The
  84 .Fn setenv
  85 function inserts or resets the environment variable
  86 .Fa name
  87 in the current environment list.
  88 If the variable
  89 .Fa name
  90 does not exist in the list,
  91 it is inserted with the given
  92 .Fa value .
  93 If the variable does exist, the argument
  94 .Fa overwrite
  95 is tested; if
  96 .Fa overwrite
  97 is
  98 zero, the
  99 variable is not reset, otherwise it is reset
 100 to the given
 101 .Fa value .
 102 .Pp
 103 The
 104 .Fn putenv
 105 function takes an argument of the form ``name=value'' and is
 106 equivalent to:
 107 .Bd -literal -offset indent
 108 setenv(name, value, 1);
 109 .Ed
 110 .Pp
 111 The
 112 .Fn unsetenv
 113 function
 114 deletes all instances of the variable name pointed to by
 115 .Fa name
 116 from the list.
 117 .Sh RETURN VALUES
 118 .Rv -std setenv putenv
 119 .Sh ERRORS
 120 .Bl -tag -width Er
 121 .It Bq Er ENOMEM
 122 The function
 123 .Fn setenv
 124 or
 125 .Fn putenv
 126 failed because they were unable to allocate memory for the environment.
 127 .El
 128 .Sh SEE ALSO
 129 .Xr csh 1 ,
 130 .Xr sh 1 ,
 131 .Xr execve 2 ,
 132 .Xr environ 7
 133 .Sh STANDARDS
 134 The
 135 .Fn getenv
 136 function conforms to
 137 .St -isoC .
 138 .Sh BUGS
 139 Successive calls to
 140 .Fn setenv
 141 or
 142 .Fn putenv
 143 assigning a differently sized
 144 .Fa value
 145 to the same
 146 .Fa name
 147 will result in a memory leak.  The
 148 .Fx
 149 semantics for these functions
 150 (namely, that the contents of
 151 .Fa value
 152 are copied and that old values remain accessible indefinitely) make this
 153 bug unavoidable.  Future versions may eliminate one or both of these
 154 semantic guarantees in order to fix the bug.
 155 .Sh HISTORY
 156 The functions
 157 .Fn setenv
 158 and
 159 .Fn unsetenv
 160 appeared in
 161 .At v7 .
 162 The
 163 .Fn putenv
 164 function appeared in
 165 .Bx 4.3 Reno .