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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
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NAME
realpath — resolve a pathname
SYNOPSIS
#include <stdlib.h>
char *realpath(const char *restrict file_name,
char *restrict resolved_name);
DESCRIPTION
The realpath() function shall derive, from the pathname pointed to by file_name, an
absolute pathname that resolves to the same directory entry, whose resolution does not
involve '.', '..', or symbolic links. If resolved_name is a null pointer, the generated
pathname shall be stored as a null-terminated string in a buffer allocated as if by a call
to malloc(). Otherwise, if {PATH_MAX} is defined as a constant in the <limits.h> header,
then the generated pathname shall be stored as a null-terminated string, up to a maximum
of {PATH_MAX} bytes, in the buffer pointed to by resolved_name.
If resolved_name is not a null pointer and {PATH_MAX} is not defined as a constant in the
<limits.h> header, the behavior is undefined.
RETURN VALUE
Upon successful completion, realpath() shall return a pointer to the buffer containing the
resolved name. Otherwise, realpath() shall return a null pointer and set errno to
indicate the error.
If the resolved_name argument is a null pointer, the pointer returned by realpath() can be
passed to free().
If the resolved_name argument is not a null pointer and the realpath() function fails, the
contents of the buffer pointed to by resolved_name are undefined.
ERRORS
The realpath() function shall fail if:
EACCES Search permission was denied for a component of the path prefix of file_name.
EINVAL The file_name argument is a null pointer.
EIO An error occurred while reading from the file system.
ELOOP A loop exists in symbolic links encountered during resolution of the file_name
argument.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT A component of file_name does not name an existing file or file_name points to an
empty string.
ENOTDIR
A component of the path prefix names an existing file that is neither a directory
nor a symbolic link to a directory, or the file_name argument contains at least one
non-<slash> character and ends with one or more trailing <slash> characters and the
last pathname component names an existing file that is neither a directory nor a
symbolic link to a directory.
The realpath() function may fail if:
EACCES The file_name argument does not begin with a <slash> and none of the symbolic links
(if any) processed during pathname resolution of file_name had contents that began
with a <slash>, and either search permission was denied for the current directory
or read or search permission was denied for a directory above the current directory
in the file hierarchy.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the
file_name argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic
link produced an intermediate result with a length that exceeds {PATH_MAX}.
ENOMEM Insufficient storage space is available.
The following sections are informative.
EXAMPLES
Generating an Absolute Pathname
The following example generates an absolute pathname for the file identified by the
symlinkpath argument. The generated pathname is stored in the buffer pointed to by
actualpath.
#include <stdlib.h>
...
char *symlinkpath = "/tmp/symlink/file";
char *actualpath;
actualpath = realpath(symlinkpath, NULL);
if (actualpath != NULL)
{
... use actualpath ...
free(actualpath);
}
else
{
... handle error ...
}
APPLICATION USAGE
For functions that allocate memory as if by malloc(), the application should release such
memory when it is no longer required by a call to free(). For realpath(), this is the
return value.
RATIONALE
Since realpath() has no length argument, if {PATH_MAX} is not defined as a constant in
<limits.h>, applications have no way of determining how large a buffer they need to
allocate for it to be safe to pass to realpath(). A {PATH_MAX} value obtained from a
prior pathconf() call is out-of-date by the time realpath() is called. Hence the only
reliable way to use realpath() when {PATH_MAX} is not defined in <limits.h> is to pass a
null pointer for resolved_name so that realpath() will allocate a buffer of the necessary
size.
FUTURE DIRECTIONS
None.
SEE ALSO
fpathconf(), free(), getcwd(), sysconf()
The Base Definitions volume of POSIX.1‐2017, <limits.h>, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .