mirror of https://github.com/mkerrisk/man-pages
139 lines
4.4 KiB
Plaintext
139 lines
4.4 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "READLINK" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" readlink
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.SH NAME
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readlink \- read the contents of a symbolic link
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.SH SYNOPSIS
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.LP
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\fB#include <unistd.h>
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.br
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.sp
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ssize_t readlink(const char *restrict\fP \fIpath\fP\fB, char *restrict\fP
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\fIbuf\fP\fB,
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.br
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\ \ \ \ \ \ size_t\fP \fIbufsize\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIreadlink\fP() function shall place the contents of the symbolic
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link referred to by \fIpath\fP in the buffer \fIbuf\fP
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which has size \fIbufsize\fP. If the number of bytes in the symbolic
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link is less than \fIbufsize\fP, the contents of the
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remainder of \fIbuf\fP are unspecified. If the \fIbuf\fP argument
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is not large enough to contain the link content, the first
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\fIbufsize\fP bytes shall be placed in \fIbuf\fP.
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.LP
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If the value of \fIbufsize\fP is greater than {SSIZE_MAX}, the result
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is implementation-defined.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIreadlink\fP() shall return the count
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of bytes placed in the buffer. Otherwise, it shall return a
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value of -1, leave the buffer unchanged, and set \fIerrno\fP to indicate
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the error.
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.SH ERRORS
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.LP
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The \fIreadlink\fP() function shall fail if:
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.TP 7
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.B EACCES
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Search permission is denied for a component of the path prefix of
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\fIpath\fP.
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.TP 7
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.B EINVAL
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The \fIpath\fP argument names a file that is not a symbolic link.
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.TP 7
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.B EIO
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An I/O error occurred while reading from the file system.
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.TP 7
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.B ELOOP
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A loop exists in symbolic links encountered during resolution of the
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\fIpath\fP argument.
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.TP 7
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.B ENAMETOOLONG
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The length of the \fIpath\fP argument exceeds {PATH_MAX} or a pathname
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component is longer than {NAME_MAX}.
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.TP 7
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.B ENOENT
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A component of \fIpath\fP does not name an existing file or \fIpath\fP
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is an empty string.
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.TP 7
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.B ENOTDIR
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A component of the path prefix is not a directory.
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.sp
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.LP
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The \fIreadlink\fP() function may fail if:
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.TP 7
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.B EACCES
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Read permission is denied for the directory.
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.TP 7
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.B ELOOP
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More than {SYMLOOP_MAX} symbolic links were encountered during resolution
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of the \fIpath\fP argument.
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.TP 7
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.B ENAMETOOLONG
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As a result of encountering a symbolic link in resolution of the \fIpath\fP
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argument, the length of the substituted pathname
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string exceeded {PATH_MAX}.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Reading the Name of a Symbolic Link
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.LP
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The following example shows how to read the name of a symbolic link
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named \fB/modules/pass1\fP.
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.sp
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.RS
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.nf
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\fB#include <unistd.h>
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.sp
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char buf[1024];
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ssizet_t len;
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\&...
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if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
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buf[len] = '\\0';
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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Conforming applications should not assume that the returned contents
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of the symbolic link are null-terminated.
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.SH RATIONALE
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.LP
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Since IEEE\ Std\ 1003.1-2001 does not require any association of file
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times with symbolic links, there is no requirement
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that file times be updated by \fIreadlink\fP(). The type associated
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with \fIbufsiz\fP is a \fBsize_t\fP in order to be
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consistent with both the ISO\ C standard and the definition of \fIread\fP().
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The behavior
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specified for \fIreadlink\fP() when \fIbufsiz\fP is zero represents
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historical practice. For this case, the standard developers
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considered a change whereby \fIreadlink\fP() would return the number
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of non-null bytes contained in the symbolic link with the
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buffer \fIbuf\fP remaining unchanged; however, since the \fBstat\fP
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structure member \fIst_size\fP value can be used to
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determine the size of buffer necessary to contain the contents of
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the symbolic link as returned by \fIreadlink\fP(), this proposal
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was rejected, and the historical practice retained.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIlstat\fP() , \fIstat\fP() , \fIsymlink\fP() ,
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the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<unistd.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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