mirror of https://github.com/mkerrisk/man-pages
391 lines
10 KiB
Groff
391 lines
10 KiB
Groff
.\" Copyright (c) 1993 Michael Haardt (michael@moria.de)
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.\" and copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
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.\" and copyright (c) 2006 Justin Pryzby <justinpryzby@users.sf.net>
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.\" and copyright (c) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, write to the Free
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.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
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.\" USA.
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.\"
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.\" Modified Sun Jul 25 11:02:22 1993 by Rik Faith (faith@cs.unc.edu)
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.\" 2006-05-24, Justin Pryzby <justinpryzby@users.sf.net>
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.\" document FTW_ACTIONRETVAL; include .SH "RETURN VALUE";
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.\" 2006-05-24, Justin Pryzby <justinpryzby@users.sf.net> and
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.\" Michael Kerrisk <mtk.manpages@gmail.com>
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.\" reorganized and rewrote much of the page
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.\" 2006-05-24, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added an example program.
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.TH FTW 3 2007-07-26 "Linux" "Linux Programmer's Manual"
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.SH NAME
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ftw, nftw \- file tree walk
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.SH SYNOPSIS
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.nf
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.B #include <ftw.h>
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.sp
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.BI "int ftw(const char *" dirpath ,
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.BI " int (*" fn ") (const char *" fpath ", const struct stat *" sb ,
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.BI " int " typeflag ),
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.BI " int " nopenfd );
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.sp
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.B #define _XOPEN_SOURCE 500
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.B #include <ftw.h>
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.sp
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.BI "int nftw(const char *" dirpath ,
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.BI " int (*" fn ") (const char *" fpath ", const struct stat *" sb ,
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.BI " int " typeflag ", struct FTW *" ftwbuf ),
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.BI " int " nopenfd ", int " flags );
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.fi
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.SH DESCRIPTION
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.BR ftw ()
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walks through the directory tree that is
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located under the directory \fIdirpath\fP,
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and calls \fIfn\fP() once for each entry in the tree.
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By default, directories are handled before the files and
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subdirectories they contain (pre-order traversal).
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To avoid using up all of the calling process's file descriptors,
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\fInopenfd\fP specifies the maximum number of directories that
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.BR ftw ()
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will hold open simultaneously.
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When
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the search depth exceeds this,
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.BR ftw ()
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will become slower because
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directories have to be closed and reopened.
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.BR ftw ()
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uses at most
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one file descriptor for each level in the directory tree.
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For each entry found in the tree,
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.BR ftw ()
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calls
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\fIfn\fP() with three arguments:
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.IR fpath ,
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.IR sb ,
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and
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.IR typeflag .
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.I fpath
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is the pathname of the entry relative to
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.IR dirpath .
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.I sb
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is a pointer to the
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.I stat
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structure returned by a call to
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.BR stat (2)
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for
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.IR fpath .
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.I typeflag
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is an integer that has one of the following values:
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.TP
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.B FTW_F
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.I fpath
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is a regular file.
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.TP
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.B FTW_D
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.I fpath
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is a directory.
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.TP
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.B FTW_DNR
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.I fpath
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is a directory which can't be read.
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.TP
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.B FTW_NS
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The
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.BR stat (2)
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call failed on
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.IR fpath ,
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which is not a symbolic link.
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.sp
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If
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.I fpath
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is a symbolic link and
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.BR stat (2)
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failed, POSIX.1-2001 states
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that it is undefined whether \fBFTW_NS\fP or \fBFTW_SL\fP (see below)
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is passed in
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.IR typeflag .
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.PP
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To stop the tree walk, \fIfn\fP() returns a non-zero value; this
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value will become the return value of
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.BR ftw ().
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As long as \fIfn\fP() returns 0,
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.BR ftw ()
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will continue either until it has traversed the entire tree,
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in which case it will return zero,
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or until it encounters an error (such as a
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.BR malloc (3)
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failure), in which case it will return \-1.
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.PP
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Because
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.BR ftw ()
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uses dynamic data structures, the only safe way to
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exit out of a tree walk is to return a non-zero value from \fIfn\fP().
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To allow a signal to terminate the walk without causing a memory leak,
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have the handler set a global flag that is checked by \fIfn\fP().
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\fIDon't\fP use
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.BR longjmp (3)
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unless the program is going to terminate.
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.SS nftw()
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The function
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.BR nftw ()
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is the same as
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.BR ftw (),
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except that it has one additional argument, \fIflags\fP,
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and calls \fIfn\fP() with one more argument, \fIftwbuf\fP.
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This \fIflags\fP argument is formed by ORing zero or more of the
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following flags:
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.TP
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.BR FTW_ACTIONRETVAL " (since glibc 2.3.3)"
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If this glibc-specific flag is set, then
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.BR nftw ()
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handles the return value from
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.IR fn ()
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differently.
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.IR fn ()
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should return one of the following values:
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.RS
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.TP
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.B FTW_CONTINUE
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Instructs
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.BR nftw ()
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to continue normally.
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.TP
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.B FTW_SKIP_SIBLINGS
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If \fIfn\fP() returns this value, then
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siblings of the current entry will be skipped,
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and processing continues in the parent.
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.\" If \fBFTW_DEPTH\fP
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.\" is set, the entry's parent directory is processed next (with
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.\" \fIflag\fP set to \fBFTW_DP\fP).
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.TP
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.B FTW_SKIP_SUBTREE
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If \fIfn\fP() is called with an entry that is a directory
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(\fItypeflag\fP is \fBFTW_D\fP), this return
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value will prevent objects within that directory from being passed as
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arguments to \fIfn\fP().
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.BR nftw ()
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continues processing with the next sibling of the directory.
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.TP
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.B FTW_STOP
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Causes
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.BR nftw ()
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to return immediately with the return value
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\fBFTW_STOP\fP.
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.PP
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Other return values could be associated with new actions in the future;
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\fIfn\fP() should not return values other than those listed above.
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The feature test macro
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.B _GNU_SOURCE
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must be defined in order to
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obtain the definition of \fBFTW_ACTIONRETVAL\fP from \fI<ftw.h>\fP.
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.RE
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.TP
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.B FTW_CHDIR
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If set, do a
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.BR chdir (2)
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to each directory before handling its contents.
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This is useful if the program needs to perform some action
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in the directory in which \fIfpath\fP resides.
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.TP
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.B FTW_DEPTH
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If set, do a post-order traversal, that is, call \fIfn\fP() for
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the directory itself \fIafter\fP handling the contents of the directory
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and its subdirectories.
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(By default, each directory is handled \fIbefore\fP its contents.)
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.TP
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.B FTW_MOUNT
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If set, stay within the same file system
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(i.e., do not cross mount points).
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.TP
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.B FTW_PHYS
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If set, do not follow symbolic links.
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(This is what you want.)
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If not set, symbolic links are followed, but no file is reported twice.
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.sp
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If \fBFTW_PHYS\fP is not set, but \fBFTW_DEPTH\fP is set,
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then the function
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.IR fn ()
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is never called for a directory that would be a descendant of itself.
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.LP
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For each entry in the directory tree,
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.BR nftw ()
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calls
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.IR fn ()
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with four arguments.
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.I fpath
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and
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.I sb
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are as for
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.BR ftw ().
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.I typeflag
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may receive any of the same values as with
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.BR ftw (),
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or any of the following values:
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.TP
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.B FTW_DP
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.I fpath
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is a directory, and \fBFTW_DEPTH\fP was specified in \fIflags\fP.
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All of the files
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and subdirectories within \fIfpath\fP have been processed.
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.TP
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.B FTW_SL
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.I fpath
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is a symbolic link, and \fBFTW_PHYS\fP was set in \fIflags\fP.
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.\" To obtain the definition of this constant from
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.\" .IR <ftw.h> ,
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.\" either
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.\" .B _BSD_SOURCE
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.\" must be defined, or
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.\" .BR _XOPEN_SOURCE
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.\" must be defined with a value of 500 or more.
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.TP
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.B FTW_SLN
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.I fpath
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is a symbolic link pointing to a nonexistent file.
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(This occurs only if \fBFTW_PHYS\fP is not set.)
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.LP
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The fourth argument that
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.BR nftw ()
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supplies when calling
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\fIfn\fP()
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is a structure of type \fIFTW\fP:
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.in +4n
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.nf
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struct FTW {
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int base;
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int level;
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};
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.fi
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.in
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.I base
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is the offset of the filename (i.e., basename component)
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in the pathname given in
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.IR fpath .
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.I level
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is the depth of
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.I fpath
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in the directory tree, relative to the root of the tree
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.RI ( dirpath ,
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which has depth 0).
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.SH "RETURN VALUE"
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These functions return 0 on success, and \-1 if an error occurs.
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If \fIfn\fP() returns non-zero,
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then the tree walk is terminated and the value returned by \fIfn\fP()
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is returned as the result of
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.BR ftw ()
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or
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.BR nftw ().
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If
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.BR nftw ()
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is called with the \fBFTW_ACTIONRETVAL\fP flag,
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then the only non-zero value that should be used by \fIfn\fP()
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to terminate the tree walk is \fBFTW_STOP\fP,
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and that value is returned as the result of
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.BR nftw ().
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.SH "CONFORMING TO"
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POSIX.1-2001, SVr4, SUSv1.
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.\" FIXME . Mar 08: The next POSIX.1 revisions marks ftw() obsolete.
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.SH NOTES
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The function
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.BR nftw ()
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and the use of \fBFTW_SL\fP with
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.BR ftw ()
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were introduced in SUSv1.
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.LP
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On some systems
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.BR ftw ()
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will never use \fBFTW_SL\fP, on other systems \fBFTW_SL\fP occurs only
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for symbolic links that do not point to an existing file,
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and again on other systems
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.BR ftw ()
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will use \fBFTW_SL\fP for each symbolic link.
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For predictable control, use
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.BR nftw ().
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.LP
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Under Linux, libc4 and libc5 and glibc 2.0.6 will
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use \fBFTW_F\fP for all objects (files, symbolic links, FIFOs, etc.)
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that can be stat'ed but are not a directory.
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The function
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.BR nftw ()
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is available since glibc 2.1.
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\fBFTW_ACTIONRETVAL\fP is glibc-specific.
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.SH EXAMPLE
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The following program traverses the directory tree under the path named
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in its first command-line argument, or under the current directory
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if no argument is supplied.
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It displays various information about each file.
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The second command-line argument can be used to specify characters that
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control the value assigned to the \fIflags\fP
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argument when calling
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.BR nftw ().
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.nf
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#define _XOPEN_SOURCE 500
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#include <ftw.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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static int
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display_info(const char *fpath, const struct stat *sb,
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int tflag, struct FTW *ftwbuf)
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{
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printf("%\-3s %2d %7jd %\-40s %d %s\\n",
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(tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
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(tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
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(tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
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(tflag == FTW_SLN) ? "sln" : "???",
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ftwbuf\->level, (intmax_t) sb\->st_size,
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fpath, ftwbuf\->base, fpath + ftwbuf\->base);
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return 0; /* To tell nftw() to continue */
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}
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int
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main(int argc, char *argv[])
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{
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int flags = 0;
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if (argc > 2 && strchr(argv[2], \(aqd\(aq) != NULL)
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flags |= FTW_DEPTH;
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if (argc > 2 && strchr(argv[2], \(aqp\(aq) != NULL)
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flags |= FTW_PHYS;
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if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags)
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== \-1) {
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perror("nftw");
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exit(EXIT_FAILURE);
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}
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH "SEE ALSO"
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.BR stat (2),
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.BR fts (3),
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.BR readdir (3),
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.BR feature_test_macros (7)
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