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.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:26:16 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Thu Apr 11 17:11:33 1996 by Andries Brouwer (aeb@cwi.nl):
.\"     Corrected type of compar routines, as suggested by
.\"     Miguel Barreiro (enano@avalon.yaix.es).  Added example.
.\" Modified Sun Sep 24 20:15:46 2000 by aeb, following Petter Reinholdtsen.
.\" Modified 2001-12-26 by aeb, following Joey. Added versionsort.
.\"
.\" The pieces on scandirat(3) were copyright and licensed as follows.
.\"
.\" Copyright (c) 2012, Mark R. Bannister <cambridge@users.sourceforge.net>
.\"        based on text in mkfifoat.3 Copyright (c) 2006, Michael Kerrisk
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH SCANDIR 3  2021-08-27 "Linux man-pages (unreleased)"
.SH NAME
scandir, scandirat, alphasort, versionsort \- scan
a directory for matching entries
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <dirent.h>
.PP
.BI "int scandir(const char *restrict " dirp ,
.BI "            struct dirent ***restrict " namelist ,
.BI "            int (*" filter ")(const struct dirent *),"
.BI "            int (*" compar ")(const struct dirent **,"
.B "                          const struct dirent **));"
.PP
.BI "int alphasort(const struct dirent **" a ", const struct dirent **" b );
.BI "int versionsort(const struct dirent **" a ", const struct dirent **" b );
.PP
.BR "#include <fcntl.h>" "          /* Definition of AT_* constants */"
.B #include <dirent.h>
.PP
.BI "int scandirat(int " dirfd ", const char *restrict " dirp ,
.BI "            struct dirent ***restrict " namelist ,
.BI "            int (*" filter ")(const struct dirent *),"
.BI "            int (*" compar ")(const struct dirent **,"
.B "                          const struct dirent **));"
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR scandir (),
.BR alphasort ():
.nf
    /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
        || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.PP
.BR versionsort ():
.nf
    _GNU_SOURCE
.fi
.PP
.BR scandirat ():
.nf
    _GNU_SOURCE
.fi
.SH DESCRIPTION
The
.BR scandir ()
function scans the directory \fIdirp\fP, calling
\fIfilter\fP() on each directory entry.
Entries for which
\fIfilter\fP() returns nonzero are stored in strings allocated via
.BR malloc (3),
sorted using
.BR qsort (3)
with the comparison
function \fIcompar\fP(), and collected in array \fInamelist\fP
which is allocated via
.BR malloc (3).
If \fIfilter\fP is NULL, all entries are selected.
.PP
The
.BR alphasort ()
and
.BR versionsort ()
functions can be used as the comparison function
.IR compar ().
The former sorts directory entries using
.BR strcoll (3),
the latter using
.BR strverscmp (3)
on the strings \fI(*a)\->d_name\fP and \fI(*b)\->d_name\fP.
.SS scandirat()
The
.BR scandirat ()
function operates in exactly the same way as
.BR scandir (),
except for the differences described here.
.PP
If the pathname given in
.I dirp
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR scandir ()
for a relative pathname).
.PP
If
.I dirp
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I dirp
is interpreted relative to the current working
directory of the calling process (like
.BR scandir ()).
.PP
If
.I dirp
is absolute, then
.I dirfd
is ignored.
.PP
See
.BR openat (2)
for an explanation of the need for
.BR scandirat ().
.SH RETURN VALUE
The
.BR scandir ()
function returns the number of directory entries
selected.
On error, \-1 is returned, with
.I errno
set to indicate the error.
.PP
The
.BR alphasort ()
and
.BR versionsort ()
functions return an integer less than, equal to,
or greater than zero if the first argument is considered to be
respectively less than, equal to, or greater than the second.
.SH ERRORS
.TP
.B EBADF
.RB ( scandirat ())
.I dirp
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B ENOENT
The path in \fIdirp\fR does not exist.
.TP
.B ENOMEM
Insufficient memory to complete the operation.
.TP
.B ENOTDIR
The path in \fIdirp\fR is not a directory.
.TP
.B ENOTDIR
.RB ( scandirat ())
.I dirp
is a relative pathname and
.I dirfd
is a file descriptor referring to a file other than a directory.
.SH VERSIONS
.BR versionsort ()
was added to glibc in version 2.1.
.PP
.BR scandirat ()
was added to glibc in version 2.15.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR scandir (),
.BR scandirat ()
T}	Thread safety	MT-Safe
T{
.BR alphasort (),
.BR versionsort ()
T}	Thread safety	MT-Safe locale
.TE
.hy
.ad
.sp 1
.SH STANDARDS
.BR alphasort (),
.BR scandir ():
4.3BSD, POSIX.1-2008.
.PP
.BR versionsort ()
and
.BR scandirat ()
are GNU extensions.
.\" .LP
.\" The functions
.\" .BR scandir ()
.\" and
.\" .BR alphasort ()
.\" are from 4.3BSD, and have been available under Linux since libc4.
.\" Libc4 and libc5 use the more precise prototype
.\" .sp
.\" .nf
.\"    int alphasort(const struct dirent ** a,
.\"                  const struct dirent **b);
.\" .fi
.\" .sp
.\" but glibc 2.0 returns to the imprecise BSD prototype.
.SH NOTES
Since glibc 2.1,
.BR alphasort ()
calls
.BR strcoll (3);
earlier it used
.BR strcmp (3).
.PP
Before glibc 2.10, the two arguments of
.BR alphasort ()
and
.BR versionsort ()
were typed as
.IR "const void\ *" .
When
.BR alphasort ()
was standardized in POSIX.1-2008,
the argument type was specified as the type-safe
.IR "const struct dirent\ **",
and glibc 2.10 changed the definition of
.BR alphasort ()
(and the nonstandard
.BR versionsort ())
to match the standard.
.SH EXAMPLES
The program below prints a list of the files in the current directory
in reverse order.
.\"
.SS Program source
\&
.EX
#define _DEFAULT_SOURCE
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
    struct dirent **namelist;
    int n;

    n = scandir(".", &namelist, NULL, alphasort);
    if (n == \-1) {
        perror("scandir");
        exit(EXIT_FAILURE);
    }

    while (n\-\-) {
        printf("%s\en", namelist[n]\->d_name);
        free(namelist[n]);
    }
    free(namelist);

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR closedir (3),
.BR fnmatch (3),
.BR opendir (3),
.BR readdir (3),
.BR rewinddir (3),
.BR seekdir (3),
.BR strcmp (3),
.BR strcoll (3),
.BR strverscmp (3),
.BR telldir (3)