Manpage of REALPATH
REALPATHSection: Linux Programmer's Manual (3)
NAMErealpath - return the canonicalized absolute pathname
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- _XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
DESCRIPTIONrealpath() expands all symbolic links and resolves references to /./, /../and extra aq/aq characters in the null-terminated string named by pathto produce a canonicalized absolute pathname. The resulting pathname is stored as a null-terminated string, up to a maximum of PATH_MAXbytes, in the buffer pointed to by resolved_path. The resulting path will have no symbolic link, /./or /../components.
If resolved_pathis specified as NULL, then realpath() uses malloc(3) to allocate a buffer of up to PATH_MAXbytes to hold the resolved pathname, and returns a pointer to this buffer. The caller should deallocate this buffer using free(3).
RETURN VALUEIf there is no error, realpath() returns a pointer to the resolved_path.
- Read or search permission was denied for a component of the path prefix.
- pathis NULL. (In glibc versions before 2.3, this error is also returned if resolved_pathis NULL.)
- An I/O error occurred while reading from the filesystem.
- Too many symbolic links were encountered in translating the pathname.
- A component of a pathname exceeded NAME_MAXcharacters, or an entire pathname exceeded PATH_MAXcharacters.
- Out of memory.
- The named file does not exist.
- A component of the path prefix is not a directory.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TO4.4BSD, POSIX.1-2001.
NOTESIn 4.4BSD and Solaris, the limit on the pathname length is MAXPATHLEN(found in <sys/param.h>). SUSv2 prescribes PATH_MAXand 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 extensionsIf the call fails with either EACCESor ENOENTand resolved_pathis not NULL, then the prefix of paththat is not readable or does not exist is returned in resolved_path.
BUGSThe 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_MAXsuffices, but PATH_MAXneed 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_MAXis not bounded. The resolved_path == NULLfeature, not standardized in POSIX.1-2001, but standardized in POSIX.1-2008, allows this design problem to be avoided.
SEE ALSOrealpath(1), readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3), sysconf(3)
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