Free Knowledge Resources


Linux Manual Pages


Free Software * Books

Source Code

Free Media

Linux

realpath(3)


NAME

   realpath - return the canonicalized absolute pathname

SYNOPSIS

   #include <limits.h>
   #include <stdlib.h>

   char *realpath(const char *path, char *resolved_path);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   realpath():
       _XOPEN_SOURCE >= 500
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE

DESCRIPTION

   realpath()  expands  all symbolic links and resolves references to /./,
   /../ and extra '/' characters in the null-terminated  string  named  by
   path  to  produce  a  canonicalized  absolute  pathname.  The resulting
   pathname is stored as a null-terminated string,  up  to  a  maximum  of
   PATH_MAX  bytes,  in  the  buffer  pointed  to  by  resolved_path.  The
   resulting path will have no symbolic link, /./ or /../ components.

   If resolved_path is specified as NULL, then realpath()  uses  malloc(3)
   to  allocate  a  buffer  of  up  to PATH_MAX bytes to hold the resolved
   pathname, and returns a pointer to  this  buffer.   The  caller  should
   deallocate this buffer using free(3).

RETURN VALUE

   If   there   is   no   error,  realpath()  returns  a  pointer  to  the
   resolved_path.

   Otherwise, it returns NULL, the contents of the array resolved_path are
   undefined, and errno is set to indicate the error.

ERRORS

   EACCES Read or search permission was denied for a component of the path
          prefix.

   EINVAL path is NULL.  (In glibc versions before 2.3, this error is also
          returned if resolved_path is NULL.)

   EIO    An I/O error occurred while reading from the filesystem.

   ELOOP  Too  many  symbolic  links  were  encountered in translating the
          pathname.

   ENAMETOOLONG
          A component of a pathname exceeded NAME_MAX  characters,  or  an
          entire pathname exceeded PATH_MAX characters.

   ENOENT The named file does not exist.

   ENOMEM Out of memory.

   ENOTDIR
          A component of the path prefix is not a directory.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface   Attribute      Value   
   
   realpath()  Thread safety  MT-Safe

CONFORMING TO

   4.4BSD, POSIX.1-2001.

   POSIX.1-2001 says  that  the  behavior  if  resolved_path  is  NULL  is
   implementation-defined.   POSIX.1-2008 specifies the behavior described
   in this page.

NOTES

   In 4.4BSD and Solaris, the limit on the pathname length  is  MAXPATHLEN
   (found  in  <sys/param.h>).  SUSv2 prescribes PATH_MAX and NAME_MAX, as
   found in <limits.h> or provided by the pathconf(3) function.  A typical
   source fragment would be

       #ifdef PATH_MAX
         path_max = PATH_MAX;
       #else
         path_max = pathconf(path, _PC_PATH_MAX);
         if (path_max <= 0)
           path_max = 4096;
       #endif

   (But see the BUGS section.)

   GNU extensions
   If the call fails with either EACCES or ENOENT and resolved_path is not
   NULL, then the prefix of path that is not readable or does not exist is
   returned in resolved_path.

BUGS

   The POSIX.1-2001 standard version of this function is broken by design,
   since it is impossible to determine a  suitable  size  for  the  output
   buffer,  resolved_path.   According  to  POSIX.1-2001  a buffer of size
   PATH_MAX suffices, but PATH_MAX need not be a defined constant, and may
   have to be obtained using pathconf(3).  And asking pathconf(3) does not
   really help, since, on the one hand POSIX  warns  that  the  result  of
   pathconf(3) may be huge and unsuitable for mallocing memory, and on the
   other hand pathconf(3) may return -1 to signify that  PATH_MAX  is  not
   bounded.    The  resolved_path == NULL  feature,  not  standardized  in
   POSIX.1-2001, but standardized  in  POSIX.1-2008,  allows  this  design
   problem to be avoided.

SEE ALSO

   realpath(1),    readlink(2),    canonicalize_file_name(3),   getcwd(3),
   pathconf(3), sysconf(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/.

                              2016-10-08                       REALPATH(3)



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.


birds banner