alphasort(3)
NAME
scandir, scandirat, alphasort, versionsort - scan a directory for matching entries
SYNOPSIS
#include <dirent.h>
int scandir(const char *dirp, struct dirent ***namelist,
int (*filter)(const struct dirent *),
int (*compar)(const struct dirent **, const struct dirent **));
int alphasort(const struct dirent **a, const struct dirent **b);
int versionsort(const struct dirent **a, const struct dirent **b);
#include <fcntl.h> /* Definition of AT_* constants */
#include <dirent.h>
int scandirat(int dirfd, const char *dirp, struct dirent ***namelist,
int (*filter)(const struct dirent *),
int (*compar)(const struct dirent **, const struct dirent **));
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
scandir(), alphasort():
/* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
versionsort(): _GNU_SOURCE
scandirat(): _GNU_SOURCE
DESCRIPTION
The scandir() function scans the directory dirp, calling filter() on each directory entry. Entries for which filter() returns nonzero are stored in strings allocated via malloc(3), sorted using qsort(3) with the comparison function compar(), and collected in array namelist which is allocated via malloc(3). If filter is NULL, all entries are selected. The alphasort() and versionsort() functions can be used as the comparison function compar(). The former sorts directory entries using strcoll(3), the latter using strverscmp(3) on the strings (*a)->d_name and (*b)->d_name. scandirat() The scandirat() function operates in exactly the same way as scandir(), except for the differences described here. If the pathname given in dirp is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by scandir() for a relative pathname). If dirp is relative and dirfd is the special value AT_FDCWD, then dirp is interpreted relative to the current working directory of the calling process (like scandir()). If dirp is absolute, then dirfd is ignored. See openat(2) for an explanation of the need for scandirat().
RETURN VALUE
The scandir() function returns the number of directory entries selected. On error, -1 is returned, with errno set to indicate the cause of the error. The alphasort() and 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.
ERRORS
ENOENT The path in dirp does not exist.
ENOMEM Insufficient memory to complete the operation.
ENOTDIR
The path in dirp is not a directory.
The following additional errors can occur for scandirat():
EBADF dirfd is not a valid file descriptor.
ENOTDIR
dirp is a relative path and dirfd is a file descriptor referring
to a file other than a directory.
VERSIONS
versionsort() was added to glibc in version 2.1. scandirat() was added to glibc in version 2.15.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). Interface Attribute Value scandir(), scandirat() Thread safety MT-Safe alphasort(), versionsort() Thread safety MT-Safe locale
CONFORMING TO
alphasort(), scandir(): 4.3BSD, POSIX.1-2008. versionsort() and scandirat() are GNU extensions.
NOTES
Since glibc 2.1, alphasort() calls strcoll(3); earlier it used strcmp(3). Before glibc 2.10, the two arguments of alphasort() and versionsort() were typed as const void *. When alphasort() was standardized in POSIX.1-2008, the argument type was specified as the type-safe const struct dirent **, and glibc 2.10 changed the definition of alphasort() (and the nonstandard versionsort()) to match the standard.
EXAMPLE
#define _DEFAULT_SOURCE
/* print files in current directory in reverse order */
#include <dirent.h>
int
main(void)
{
struct dirent **namelist;
int n;
n = scandir(".", &namelist, NULL, alphasort);
if (n < 0)
perror("scandir");
else {
while (n--) {
printf("%s\n", namelist[n]->d_name);
free(namelist[n]);
}
free(namelist);
}
}
SEE ALSO
closedir(3), fnmatch(3), opendir(3), readdir(3), rewinddir(3), seekdir(3), strcmp(3), strcoll(3), strverscmp(3), telldir(3)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
