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.Dd February 2, 2020
.Dt __REALPATH 2
.Os
.Sh NAME
.Nm __realpath
.Nd resolves the canonicalized absolute pathname
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Ft "int"
.Fn __realpath "const char * restrict pathname" "char * restrict resolved_path" "size_t len"
.Sh DESCRIPTION
The
.Fn __realpath
system call is used to support the libc
.Fn realpath
library call.
It basically does the same thing but with a lower-level system-call
compatible API.
The system call differs from the libc function as follows:
It requires that the target buffer and the size of the target
buffer be supplied, it does not (obviously) allocate a target buffer if NULL
is supplied, and it returns the string length of the target buffer (not
including the terminator) or -1.
If a failure occurs, the target buffer will not be modified (whereas it is
in the libc function).
.Pp
The system call resolves all symbolic links, extra
.Dq /
characters and references to
.Pa /./
and
.Pa /../
in
.Fa pathname ,
and copies the resulting absolute pathname into
the memory pointed to by
.Fa resolved_path .
The
.Fa resolved_path
argument
.Em must
point to a buffer capable of storing at least
.Fa len
characters, and may not be
.Dv NULL .
.Pp
The
.Fn __realpath
function will resolve both absolute and relative paths
and return the absolute pathname corresponding to
.Fa pathname .
All components of
.Fa pathname
must exist when
.Fn __realpath
is called, and all but the last component must name either directories or
symlinks pointing to the directories.
.Sh "RETURN VALUES"
The
.Fn realpath
function returns
the string length of the path stored in the target buffer, not including
the terminator, or -1 on failure.
.Sh ERRORS
The function
may fail and set the external variable
.Va errno
for any of the errors specified for the library function
.Xr realpath 3 .
.Sh SEE ALSO
.Xr realpath 3
.Sh HISTORY
The
.Fn __realpath
function first appeared in
.Dx 5.7 .
.Sh CAVEATS
This is the system call version of the libc
.Fn realpath
function, but is not a replacement for the libc function due to
necessary API differences.