| .\" Copyright (C) 1999 Andries Brouwer (aeb@cwi.nl) |
| .\" |
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| .\" Rewritten old page, 990824, aeb@cwi.nl |
| .\" 2004-12-14, mtk, added discussion of resolved_path == NULL |
| .\" |
| .TH REALPATH 3 2017-09-15 "" "Linux Programmer's Manual" |
| .SH NAME |
| realpath \- return the canonicalized absolute pathname |
| .SH SYNOPSIS |
| .nf |
| .B #include <limits.h> |
| .B #include <stdlib.h> |
| .PP |
| .BI "char *realpath(const char *" path ", char *" resolved_path ); |
| .fi |
| .PP |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .PP |
| .BR realpath (): |
| .ad l |
| .RS 4 |
| _XOPEN_SOURCE\ >=\ 500 |
| .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
| || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE |
| .RE |
| .ad |
| .SH DESCRIPTION |
| .BR realpath () |
| expands all symbolic links and resolves references |
| to |
| .IR "/./" ", " "/../" |
| and extra \(aq/\(aq |
| characters in the null-terminated string named by |
| .I path |
| to produce a canonicalized absolute pathname. |
| The resulting pathname is stored as a null-terminated string, |
| up to a maximum of |
| .B PATH_MAX |
| bytes, |
| in the buffer pointed to by |
| .IR resolved_path . |
| The resulting path will have no symbolic link, |
| .I "/./" |
| or |
| .I "/../" |
| components. |
| .PP |
| If |
| .I resolved_path |
| is specified as NULL, then |
| .BR realpath () |
| uses |
| .BR malloc (3) |
| to allocate a buffer of up to |
| .B PATH_MAX |
| bytes to hold the resolved pathname, |
| and returns a pointer to this buffer. |
| The caller should deallocate this buffer using |
| .BR free (3). |
| .\" Even if we use resolved_path == NULL, then realpath() will still |
| .\" return ENAMETOOLONG if the resolved pathname would exceed PATH_MAX |
| .\" bytes -- MTK, Dec 04 |
| .\" .SH HISTORY |
| .\" The |
| .\" .BR realpath () |
| .\" function first appeared in 4.4BSD, contributed by Jan-Simon Pendry. |
| .SH RETURN VALUE |
| If there is no error, |
| .BR realpath () |
| returns a pointer to the |
| .IR resolved_path . |
| .PP |
| Otherwise, it returns NULL, the contents |
| of the array |
| .I resolved_path |
| are undefined, and |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EACCES |
| Read or search permission was denied for a component of the path prefix. |
| .TP |
| .B EINVAL |
| .I path |
| is NULL. |
| .\" (In libc5 this would just cause a segfault.) |
| (In glibc versions before 2.3, |
| this error is also returned if |
| .IR resolved_path |
| is NULL.) |
| .TP |
| .B EIO |
| An I/O error occurred while reading from the filesystem. |
| .TP |
| .B ELOOP |
| Too many symbolic links were encountered in translating the pathname. |
| .TP |
| .B ENAMETOOLONG |
| A component of a pathname exceeded |
| .B NAME_MAX |
| characters, or an entire pathname exceeded |
| .B PATH_MAX |
| characters. |
| .TP |
| .B ENOENT |
| The named file does not exist. |
| .TP |
| .B ENOMEM |
| Out of memory. |
| .TP |
| .B ENOTDIR |
| A component of the path prefix is not a directory. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lb lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR realpath () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| 4.4BSD, POSIX.1-2001. |
| .PP |
| POSIX.1-2001 says that the behavior if |
| .I resolved_path |
| is NULL is implementation-defined. |
| POSIX.1-2008 specifies the behavior described in this page. |
| .SH NOTES |
| In 4.4BSD and Solaris, the limit on the pathname length is |
| .B MAXPATHLEN |
| (found in \fI<sys/param.h>\fP). |
| SUSv2 prescribes |
| .B PATH_MAX |
| and |
| .BR NAME_MAX , |
| as found in \fI<limits.h>\fP or provided by the |
| .BR pathconf (3) |
| function. |
| A typical source fragment would be |
| .PP |
| .in +4n |
| .EX |
| #ifdef PATH_MAX |
| path_max = PATH_MAX; |
| #else |
| path_max = pathconf(path, _PC_PATH_MAX); |
| if (path_max <= 0) |
| path_max = 4096; |
| #endif |
| .EE |
| .in |
| .PP |
| (But see the BUGS section.) |
| .PP |
| .\" 2012-05-05, According to Casper Dik, the statement about |
| .\" Solaris was not true at least as far back as 1997, and |
| .\" may never have been true. |
| .\" |
| .\" The 4.4BSD, Linux and SUSv2 versions always return an absolute |
| .\" pathname. |
| .\" Solaris may return a relative pathname when the |
| .\" .I path |
| .\" argument is relative. |
| .\" The prototype of |
| .\" .BR realpath () |
| .\" is given in \fI<unistd.h>\fP in libc4 and libc5, |
| .\" but in \fI<stdlib.h>\fP everywhere else. |
| .SS GNU extensions |
| If the call fails with either |
| .BR EACCES |
| or |
| .BR ENOENT |
| and |
| .I resolved_path |
| is not NULL, then the prefix of |
| .I path |
| that is not readable or does not exist is returned in |
| .IR resolved_path . |
| .SH 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, |
| .IR resolved_path . |
| According to POSIX.1-2001 a buffer of size |
| .B PATH_MAX |
| suffices, but |
| .B PATH_MAX |
| need not be a defined constant, and may have to be obtained using |
| .BR pathconf (3). |
| And asking |
| .BR pathconf (3) |
| does not really help, since, on the one hand POSIX warns that |
| the result of |
| .BR pathconf (3) |
| may be huge and unsuitable for mallocing memory, |
| and on the other hand |
| .BR pathconf (3) |
| may return \-1 to signify that |
| .B PATH_MAX |
| is not bounded. |
| The |
| .I "resolved_path\ ==\ NULL" |
| feature, not standardized in POSIX.1-2001, |
| but standardized in POSIX.1-2008, allows this design problem to be avoided. |
| .\" .LP |
| .\" The libc4 and libc5 implementation contained a buffer overflow |
| .\" (fixed in libc-5.4.13). |
| .\" Thus, set-user-ID programs like |
| .\" .BR mount (8) |
| .\" needed a private version. |
| .SH SEE ALSO |
| .BR realpath (1), |
| .BR readlink (2), |
| .BR canonicalize_file_name (3), |
| .BR getcwd (3), |
| .BR pathconf (3), |
| .BR sysconf (3) |
