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.Dd August 31, 2023
.Dt SCANDIR 3
.Os
.Sh NAME
.Nm scandir ,
.Nm scandirat ,
.Nm scandir_b ,
.Nm alphasort ,
.Nm versionsort
.Nd scan a directory
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In dirent.h
.Ft int
.Fo scandir
.Fa "const char *dirname"
.Fa "struct dirent ***namelist"
.Fa "int \*(lp*select\*(rp\*(lpconst struct dirent *\*(rp"
.Fa "int \*(lp*compar\*(rp\*(lpconst struct dirent **, const struct dirent **\*(rp"
.Fc
.Ft int
.Fo scandirat
.Fa "int dirfd"
.Fa "const char *dirname"
.Fa "struct dirent ***namelist"
.Fa "int \*(lp*select\*(rp\*(lpconst struct dirent *\*(rp"
.Fa "int \*(lp*compar\*(rp\*(lpconst struct dirent **, const struct dirent **\*(rp"
.Fc
.Ft int
.Fo scandir_b
.Fa "const char *dirname"
.Fa "struct dirent ***namelist"
.Fa "int \*(lp^select\*(rp\*(lpconst struct dirent *\*(rp"
.Fa "int \*(lp^compar\*(rp\*(lpconst struct dirent **, const struct dirent **\*(rp"
.Fc
.Ft int
.Fn alphasort "const struct dirent **d1" "const struct dirent **d2"
.Ft int
.Fn versionsort "const struct dirent **d1" "const struct dirent **d2"
.Sh DESCRIPTION
The
.Fn scandir
function
reads the directory
.Fa dirname
and builds an array of pointers to directory
entries using
.Xr malloc 3 .
It returns the number of entries in the array.
A pointer to the array of directory entries is stored in the location
referenced by
.Fa namelist .
.Pp
The
.Fa select
argument is a pointer to a user supplied subroutine which is called by
.Fn scandir
to select which entries are to be included in the array.
The select routine is passed a
pointer to a directory entry and should return a non-zero
value if the directory entry is to be included in the array.
If
.Fa select
is null, then all the directory entries will be included.
.Pp
The
.Fa compar
argument is a pointer to a user supplied subroutine which is passed to
.Xr qsort 3
to sort the completed array.
If this pointer is null, the array is not sorted.
.Pp
The
.Fn alphasort
function
is a routine which can be used for the
.Fa compar
argument to sort the array alphabetically using
.Xr strcoll 3 .
.Pp
The
.Fn versionsort
function is a routine which can be used for the
.Fa compar
argument to sort the array naturally using
.Xr strverscmp 3 .
.Pp
The memory allocated for the array can be deallocated with
.Xr free 3 ,
by freeing each pointer in the array and then the array itself.
.Pp
The
.Fn scandirat
function is similar to
.Fn scandir ,
but takes an additional
.Fa dirfd
argument.
If the supplied
.Fa dirname
is absolute, the function's behavior is identical to that of
.Fn scandir ,
the
.Fa dirfd
argument is unused.
If
.Fa dirname
is relative,
.Fa dirfd
must be a valid file descriptor referencing a directory, in
which case the
.Fa dirname
lookup is performed relative to the directory referenced by
.Fa dirfd .
If
.Fa dirfd
has the special value
.Va AT_FDCWD ,
then the current process directory is used as the base for
relative lookups.
See
.Xr openat 2
for additional details.
.Pp
The
.Fn scandir_b
function behaves in the same way as
.Fn scandir ,
but takes blocks as arguments instead of function pointers and calls
.Fn qsort_b
rather than
.Fn qsort .
.Sh DIAGNOSTICS
Returns \-1 if the directory cannot be opened for reading or if
.Xr malloc 3
cannot allocate enough memory to hold all the data structures.
.Sh SEE ALSO
.Xr openat 2 ,
.Xr directory 3 ,
.Xr malloc 3 ,
.Xr qsort 3 ,
.Xr strcoll 3 ,
.Xr strverscmp 3 ,
.Xr dir 5
.Sh STANDARDS
The
.Fn versionsort
function is a GNU extension and conforms to no standard.
.Sh HISTORY
The
.Fn scandir
and
.Fn alphasort
functions appeared in
.Bx 4.2 .
The
.Fn scandirat
and
.Fn versionsort
functions were added in
.Fx 13.2 .