463 lines
10 KiB
HTML
463 lines
10 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of GETCWD</TITLE>
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</HEAD><BODY>
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<H1>GETCWD</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2018-04-30<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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getcwd, getwd, get_current_dir_name - get current working directory
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<B>char *getcwd(char *</B><I>buf</I><B>, size_t </B><I>size</I><B>);</B>
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<B>char *getwd(char *</B><I>buf</I><B>);</B>
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<B>char *get_current_dir_name(void);</B>
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</PRE>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>get_current_dir_name</B>():
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<DL COMPACT><DT id="1"><DD>
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_GNU_SOURCE
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</DL>
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<P>
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<B>getwd</B>():
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<DL COMPACT><DT id="2"><DD>
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<DL COMPACT>
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<DT id="3">Since glibc 2.12:<DD>
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<PRE>
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(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
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|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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<DT id="4"></PRE>
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<DD>
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Before glibc 2.12:
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_BSD_SOURCE || _XOPEN_SOURCE >= 500
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</DL>
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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These functions return a null-terminated string containing an
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absolute pathname that is the current working directory of
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the calling process.
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The pathname is returned as the function result and via the argument
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<I>buf</I>,
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if present.
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<P>
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The
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<B>getcwd</B>()
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function copies an absolute pathname of the current working directory
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to the array pointed to by
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<I>buf</I>,
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which is of length
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<I>size</I>.
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<P>
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If the length of the absolute pathname of the current working directory,
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including the terminating null byte, exceeds
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<I>size</I>
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bytes, NULL is returned, and
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<I>errno</I>
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is set to
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<B>ERANGE</B>;
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an application should check for this error, and allocate a larger
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buffer if necessary.
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<P>
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As an extension to the POSIX.1-2001 standard, glibc's
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<B>getcwd</B>()
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allocates the buffer dynamically using
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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if
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<I>buf</I>
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is NULL.
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In this case, the allocated buffer has the length
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<I>size</I>
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unless
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<I>size</I>
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is zero, when
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<I>buf</I>
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is allocated as big as necessary.
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The caller should
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<B><A HREF="/cgi-bin/man/man2html?3+free">free</A></B>(3)
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the returned buffer.
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<P>
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<B>get_current_dir_name</B>()
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will
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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an array big enough to hold the absolute pathname of
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the current working directory.
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If the environment
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variable
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<B>PWD</B>
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is set, and its value is correct, then that value will be returned.
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The caller should
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<B><A HREF="/cgi-bin/man/man2html?3+free">free</A></B>(3)
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the returned buffer.
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<P>
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<B>getwd</B>()
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does not
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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any memory.
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The
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<I>buf</I>
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argument should be a pointer to an array at least
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<B>PATH_MAX</B>
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bytes long.
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If the length of the absolute pathname of the current working directory,
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including the terminating null byte, exceeds
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<B>PATH_MAX</B>
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bytes, NULL is returned, and
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<I>errno</I>
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is set to
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<B>ENAMETOOLONG</B>.
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(Note that on some systems,
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<B>PATH_MAX</B>
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may not be a compile-time constant;
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furthermore, its value may depend on the filesystem, see
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<B><A HREF="/cgi-bin/man/man2html?3+pathconf">pathconf</A></B>(3).)
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For portability and security reasons, use of
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<B>getwd</B>()
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is deprecated.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, these functions return a pointer to a string containing
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the pathname of the current working directory.
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In the case of
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<B>getcwd</B>()
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and
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<B>getwd</B>()
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this is the same value as
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<I>buf</I>.
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<P>
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On failure, these functions return NULL, and
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<I>errno</I>
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is set to indicate the error.
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The contents of the array pointed to by
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<I>buf</I>
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are undefined on error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="5"><B>EACCES</B>
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<DD>
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Permission to read or search a component of the filename was denied.
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<DT id="6"><B>EFAULT</B>
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<DD>
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<I>buf</I>
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points to a bad address.
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<DT id="7"><B>EINVAL</B>
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<DD>
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The
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<I>size</I>
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argument is zero and
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<I>buf</I>
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is not a null pointer.
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<DT id="8"><B>EINVAL</B>
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<DD>
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<B>getwd</B>():
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<I>buf</I>
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is NULL.
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<DT id="9"><B>ENAMETOOLONG</B>
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<DD>
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<B>getwd</B>():
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The size of the null-terminated absolute pathname string exceeds
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<B>PATH_MAX</B>
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bytes.
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<DT id="10"><B>ENOENT</B>
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<DD>
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The current working directory has been unlinked.
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<DT id="11"><B>ENOMEM</B>
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<DD>
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Out of memory.
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<DT id="12"><B>ERANGE</B>
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<DD>
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The
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<I>size</I>
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argument is less than the length of the absolute pathname of the
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working directory, including the terminating null byte.
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You need to allocate a bigger array and try again.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>getcwd</B>(),
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<B>getwd</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>get_current_dir_name</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe env<BR></TD></TR>
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</TABLE>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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<B>getcwd</B>()
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conforms to POSIX.1-2001.
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Note however that POSIX.1-2001 leaves the behavior of
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<B>getcwd</B>()
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unspecified if
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<I>buf</I>
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is NULL.
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<P>
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<B>getwd</B>()
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is present in POSIX.1-2001, but marked LEGACY.
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POSIX.1-2008 removes the specification of
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<B>getwd</B>().
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Use
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<B>getcwd</B>()
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instead.
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POSIX.1-2001
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does not define any errors for
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<B>getwd</B>().
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<P>
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<B>get_current_dir_name</B>()
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is a GNU extension.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Under Linux, these functions make use of the
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<B>getcwd</B>()
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system call (available since Linux 2.1.92).
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On older systems they would query
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<I>/proc/self/cwd</I>.
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If both system call and proc filesystem are missing, a
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generic implementation is called.
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Only in that case can
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these calls fail under Linux with
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<B>EACCES</B>.
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<P>
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These functions are often used to save the location of the current working
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directory for the purpose of returning to it later.
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Opening the current
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directory (".") and calling
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<B><A HREF="/cgi-bin/man/man2html?2+fchdir">fchdir</A></B>(2)
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to return is usually a faster and more reliable alternative when sufficiently
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many file descriptors are available, especially on platforms other than Linux.
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<A NAME="lbAJ"> </A>
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<H3>C library/kernel differences</H3>
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On Linux, the kernel provides a
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<B>getcwd</B>()
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system call, which the functions described in this page will use if possible.
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The system call takes the same arguments as the library function
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of the same name, but is limited to returning at most
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<B>PATH_MAX</B>
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bytes.
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(Before Linux 3.12,
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the limit on the size of the returned pathname was the system page size.
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On many architectures,
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<B>PATH_MAX</B>
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and the system page size are both 4096 bytes,
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but a few architectures have a larger page size.)
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If the length of the pathname of the current working directory
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exceeds this limit, then the system call fails with the error
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<B>ENAMETOOLONG</B>.
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In this case, the library functions fall back to
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a (slower) alternative implementation that returns the full pathname.
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<P>
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Following a change in Linux 2.6.36,
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the pathname returned by the
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<B>getcwd</B>()
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system call will be prefixed with the string "(unreachable)"
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if the current directory is not below the root directory of the current
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process (e.g., because the process set a new filesystem root using
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<B><A HREF="/cgi-bin/man/man2html?2+chroot">chroot</A></B>(2)
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without changing its current directory into the new root).
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Such behavior can also be caused by an unprivileged user by changing
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the current directory into another mount namespace.
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When dealing with pathname from untrusted sources, callers of the
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functions described in this page
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should consider checking whether the returned pathname starts
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with '/' or '(' to avoid misinterpreting an unreachable path
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as a relative pathname.
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<A NAME="lbAK"> </A>
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<H2>BUGS</H2>
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Since the Linux 2.6.36 change that added "(unreachable)" in the
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circumstances described above, the glibc implementation of
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<B>getcwd</B>()
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has failed to conform to POSIX and returned a relative pathname when the API
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contract requires an absolute pathname.
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With glibc 2.27 onwards this is corrected;
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calling
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<B>getcwd</B>()
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from such a pathname will now result in failure with
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<B>ENOENT</B>.
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+pwd">pwd</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+chdir">chdir</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+fchdir">fchdir</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+open">open</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+unlink">unlink</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+free">free</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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<A NAME="lbAM"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="13"><A HREF="#lbAB">NAME</A><DD>
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<DT id="14"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="15"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="16"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="17"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="18"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="19"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="20"><A HREF="#lbAI">NOTES</A><DD>
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<DL>
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<DT id="21"><A HREF="#lbAJ">C library/kernel differences</A><DD>
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</DL>
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<DT id="22"><A HREF="#lbAK">BUGS</A><DD>
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<DT id="23"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="24"><A HREF="#lbAM">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:44 GMT, March 31, 2021
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</BODY>
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</HTML>
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