man/man9/getenv.9

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.Dd October 22, 2015
.Dt GETENV 9
.Os
.Sh NAME
.Nm freeenv ,
.Nm getenv ,
.Nm getenv_int ,
.Nm getenv_long ,
.Nm getenv_string ,
.Nm getenv_quad ,
.Nm getenv_uint ,
.Nm getenv_ulong ,
.Nm setenv ,
.Nm testenv ,
.Nm unsetenv
.Nd kernel environment variable functions
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.Ft void
.Fn freeenv "char *env"
.Ft char *
.Fn getenv "const char *name"
.Ft int
.Fn getenv_int "const char *name" "int *data"
.Ft int
.Fn getenv_long "const char *name" "long *data"
.Ft int
.Fn getenv_string "const char *name" "char *data" "int size"
.Ft int
.Fn getenv_quad "const char *name" "quad_t *data"
.Ft int
.Fn getenv_uint "const char *name" "unsigned int *data"
.Ft int
.Fn getenv_ulong "const char *name" "unsigned long *data"
.Ft int
.Fn setenv "const char *name" "const char *value"
.Ft int
.Fn testenv "const char *name"
.Ft int
.Fn unsetenv "const char *name"
.Sh DESCRIPTION
These functions set, unset, fetch, and parse variables from the kernel's
environment.
.Pp
The
.Fn getenv
function obtains the current value of the kernel environment variable
.Fa name
and returns a pointer to the string value.
The caller should not modify the string pointed to by the return value.
The
.Fn getenv
function may allocate temporary storage,
so the
.Fn freeenv
function must be called to release any allocated resources when the value
returned by
.Fn getenv
is no longer needed.
.Pp
The
.Fn freeenv
function is used to release the resources allocated by a previous call to
.Fn getenv .
The
.Fa env
argument passed to
.Fn freeenv
is the pointer returned by the earlier call to
.Fn getenv .
Like
.Xr free 3 ,
the
.Fa env
argument can be
.Va NULL ,
in which case no action occurs.
.Pp
The
.Fn setenv
function inserts or resets the kernel environment variable
.Fa name
to
.Fa value .
If the variable
.Fa name
already exists,
its value is replaced.
This function can fail if an internal limit on the number of environment
variables is exceeded.
.Pp
The
.Fn unsetenv
function deletes the kernel environment variable
.Fa name .
.Pp
The
.Fn testenv
function is used to determine if a kernel environment variable exists.
It returns a non-zero value if the variable
.Fa name
exists and zero if it does not.
.Pp
The
.Fn getenv_int ,
.Fn getenv_long ,
.Fn getenv_quad ,
.Fn getenv_uint ,
and
.Fn getenv_ulong
functions look for a kernel environment variable
.Fa name
and parse it as a signed integer,
long integer,
signed 64-bit integer,
unsigned integer,
or an unsigned long integer,
respectively.
These functions fail and return zero if
.Fa name
does not exist or if any invalid characters are present in its value.
On success,
these function store the parsed value in the integer variable pointed to
by
.Fa data .
If the parsed value overflows the integer type,
a truncated value is stored in
.Fa data
and zero is returned.
If the value begins with a prefix of
.Dq 0x
it is interpreted as hexadecimal.
If it begins with a prefix of
.Dq 0
it is interpreted as octal.
Otherwise,
the value is interpreted as decimal.
The value may contain a single character suffix specifying a unit for
the value.
The interpreted value is multiplied by the unit's magnitude before being
returned.
The following unit suffixes are supported:
.Bl -column -offset indent ".Sy Unit" ".Sy Magnitude"
.It Sy Unit Ta Sy Magnitude
.It k Ta 2^10
.It m Ta 2^20
.It g Ta 2^30
.It t Ta 2^40
.El
.Pp
The
.Fn getenv_string
function stores a copy of the kernel environment variable
.Fa name
in the buffer described by
.Fa data
and
.Fa size.
If the variable does not exist,
zero is returned.
If the variable exists,
up to
.Fa size - 1
characters of its value are copied to the buffer pointed to by
.Fa data
followed by a null character and a non-zero value is returned.
.Sh RETURN VALUES
The
.Fn getenv
function returns a pointer to an environment variable's value on success or
.Dv NULL
if the variable does not exist.
.Pp
The
.Fn setenv
and
.Fn unsetenv
functions return zero on success and -1 on failure.
.Pp
The
.Fn testenv
function returns zero if the specified environment variable does not exist and
a non-zero value if it does exist.
The
.Fn getenv_int ,
.Fn getenv_long ,
.Fn getenv_string ,
.Fn getenv_quad ,
.Fn getenv_uint ,
and
.Fn getenv_ulong
functions return a non-zero value on success and zero on failure.