realpath.3p (6138B)
- '\" et
- .TH REALPATH "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- realpath
- \(em resolve a pathname
- .SH SYNOPSIS
- .LP
- .nf
- #include <stdlib.h>
- .P
- char *realpath(const char *restrict \fIfile_name\fP,
- char *restrict \fIresolved_name\fP);
- .fi
- .SH DESCRIPTION
- The
- \fIrealpath\fR()
- function shall derive, from the pathname pointed to by
- .IR file_name ,
- an absolute pathname that resolves to the same directory entry, whose
- resolution does not involve
- .BR '.' ,
- .BR '..' ,
- or symbolic links. If
- .IR 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
- \fImalloc\fR().
- Otherwise, if
- {PATH_MAX}
- is defined as a constant in the
- .IR <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
- .IR resolved_name .
- .P
- If
- .IR resolved_name
- is not a null pointer and
- {PATH_MAX}
- is not defined as a constant in the
- .IR <limits.h>
- header, the behavior is undefined.
- .SH "RETURN VALUE"
- Upon successful completion,
- \fIrealpath\fR()
- shall return a pointer to the buffer containing the resolved name.
- Otherwise,
- \fIrealpath\fR()
- shall return a null pointer and set
- .IR errno
- to indicate the error.
- .P
- If the
- .IR resolved_name
- argument is a null pointer, the pointer returned by
- \fIrealpath\fR()
- can be passed to
- \fIfree\fR().
- .P
- If the
- .IR resolved_name
- argument is not a null pointer and the
- \fIrealpath\fR()
- function fails, the contents of the buffer pointed to by
- .IR resolved_name
- are undefined.
- .SH ERRORS
- The
- \fIrealpath\fR()
- function shall fail if:
- .TP
- .BR EACCES
- Search permission was denied for a component of the path prefix of
- .IR file_name .
- .TP
- .BR EINVAL
- The
- .IR file_name
- argument is a null pointer.
- .TP
- .BR EIO
- An error occurred while reading from the file system.
- .TP
- .BR ELOOP
- A loop exists in symbolic links encountered during resolution of the
- .IR file_name
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of a component of a pathname is longer than
- {NAME_MAX}.
- .TP
- .BR ENOENT
- A component of
- .IR file_name
- does not name an existing file or
- .IR file_name
- points to an empty string.
- .TP
- .BR 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
- .IR file_name
- argument contains at least one non-\c
- <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.
- .br
- .P
- The
- \fIrealpath\fR()
- function may fail if:
- .TP
- .BR EACCES
- The
- .IR file_name
- argument does not begin with a
- <slash>
- and none of the symbolic links (if any) processed during pathname
- resolution of
- .IR 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.
- .TP
- .BR ELOOP
- More than
- {SYMLOOP_MAX}
- symbolic links were encountered during resolution of the
- .IR file_name
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- 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}.
- .TP
- .BR ENOMEM
- Insufficient storage space is available.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- .SS "Generating an Absolute Pathname"
- .P
- The following example generates an absolute pathname for the file
- identified by the
- .IR symlinkpath
- argument. The generated pathname is stored in the buffer pointed to by
- .IR actualpath .
- .sp
- .RS 4
- .nf
- #include <stdlib.h>
- \&...
- char *symlinkpath = "/tmp/symlink/file";
- char *actualpath;
- .P
- actualpath = realpath(symlinkpath, NULL);
- if (actualpath != NULL)
- {
- ... use actualpath ...
- .P
- free(actualpath);
- }
- else
- {
- ... handle error ...
- }
- .fi
- .P
- .RE
- .SH "APPLICATION USAGE"
- For functions that allocate memory as if by
- \fImalloc\fR(),
- the application should release such memory when it is no longer
- required by a call to
- \fIfree\fR().
- For
- \fIrealpath\fR(),
- this is the return value.
- .SH RATIONALE
- Since
- \fIrealpath\fR()
- has no
- .IR length
- argument, if
- {PATH_MAX}
- is not defined as a constant in
- .IR <limits.h> ,
- applications have no way of determining how large a buffer they need
- to allocate for it to be safe to pass to
- \fIrealpath\fR().
- A
- {PATH_MAX}
- value obtained from a prior
- \fIpathconf\fR()
- call is out-of-date by the time
- \fIrealpath\fR()
- is called. Hence the only reliable way to use
- \fIrealpath\fR()
- when
- {PATH_MAX}
- is not defined in
- .IR <limits.h>
- is to pass a null pointer for
- .IR resolved_name
- so that
- \fIrealpath\fR()
- will allocate a buffer of the necessary size.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIfpathconf\fR\^(\|)",
- .IR "\fIfree\fR\^(\|)",
- .IR "\fIgetcwd\fR\^(\|)",
- .IR "\fIsysconf\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<limits.h>\fP",
- .IR "\fB<stdlib.h>\fP"
- .\"
- .SH 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 .
- .PP
- 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 .