libc/gen/ftw.3

.\"	$OpenBSD: ftw.3,v 1.5 2004/01/25 14:48:32 jmc Exp $
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.\" Copyright (c) 2003 Todd C. Miller <Todd.Miller@courtesan.com>
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.Dd March 12, 2020
.Dt FTW 3
.Os
.Sh NAME
.Nm ftw , nftw
.Nd traverse (walk) a file tree
.Sh SYNOPSIS
.In ftw.h
.Ft int
.Fo ftw
.Fa "const char *path"
.Fa "int \*[lp]*fn\*[rp]\*[lp]const char *, const struct stat *, int\*[rp]"
.Fa "int maxfds"
.Fc
.Ft int
.Fo nftw
.Fa "const char *path"
.Fa "int \*[lp]*fn\*[rp]\*[lp]const char *, const struct stat *, int, struct FTW *\*[rp]"
.Fa "int maxfds"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
The
.Fn ftw
and
.Fn nftw
functions traverse (walk) the directory hierarchy rooted in
.Fa path .
For each object in the hierarchy, these functions call the function
pointed to by
.Fa fn .
The
.Fn ftw
function passes this function a pointer to a
.Dv NUL Ns
-terminated string containing
the name of the object, a pointer to a
.Vt stat
structure corresponding to the
object, and an integer flag.
The
.Fn nftw
function passes the aforementioned arguments plus a pointer to a
.Vt FTW
structure as defined by
.In ftw.h
(shown below):
.Bd -literal
struct FTW {
    int base;	/* offset of basename into pathname */
    int level;	/* directory depth relative to starting point */
};
.Ed
.Pp
Possible values for the flag passed to
.Fa fn
are:
.Bl -tag -width ".Dv FTW_DNR"
.It Dv FTW_F
A regular file.
.It Dv FTW_D
A directory being visited in pre-order.
.It Dv FTW_DNR
A directory which cannot be read.
The directory will not be descended into.
.It Dv FTW_DP
A directory being visited in post-order
.Po Fn nftw
only
.Pc .
.It Dv FTW_NS
A file for which no
.Xr stat 2
information was available.
The contents of the
.Vt stat
structure are undefined.
.It Dv FTW_SL
A symbolic link.
.It Dv FTW_SLN
A symbolic link with a non-existent target
.Po Fn nftw
only
.Pc .
.El
.Pp
The
.Fn ftw
function traverses the tree in pre-order.
That is, it processes the directory before the directory's contents.
.Pp
The
.Fa maxfds
argument specifies the maximum number of file descriptors
to keep open while traversing the tree.
It has no effect in this implementation.
.Pp
The
.Fn nftw
function has an additional
.Fa flags
argument with the following possible values:
.Bl -tag -width ".Dv FTW_MOUNT"
.It Dv FTW_PHYS
Physical walk, do not follow symbolic links.
.It Dv FTW_MOUNT
The walk will not cross a mount point.
.It FTW_DEPTH
Process directories in post-order.
Contents of a directory are visited before the directory itself.
By default,
.Fn nftw
traverses the tree in pre-order.
.It FTW_CHDIR
Change to a directory before reading it.
By default,
.Fn nftw
will change its starting directory.
The current working directory will be restored to its original value before
.Fn nftw
returns.
.El
.Sh RETURN VALUES
If the tree was traversed successfully, the
.Fn ftw
and
.Fn nftw
functions return 0.
If the function pointed to by
.Fa fn
returns a non-zero value,
.Fn ftw
and
.Fn nftw
will stop processing the tree and return the value from
.Fa fn .
Both functions return \-1 if an error is detected.
.Sh EXAMPLES
Following there is an example that shows how
.Nm nftw
can be used.
It traverses the file tree starting at the directory pointed
by the only program argument and shows the complete path and a brief
indicator about the file type.
.Bd -literal -offset 2n
#include <ftw.h>
#include <stdio.h>
#include <sysexits.h>

int
nftw_callback(const char *path, const struct stat *sb, int typeflag, struct FTW *ftw)
{
	char type;

	switch(typeflag) {
	case FTW_F:
		type = 'F';
		break;
	case FTW_D:
		type = 'D';
		break;
	case FTW_DNR:
		type = '-';
		break;
	case FTW_DP:
		type = 'd';
		break;
	case FTW_NS:
		type = 'X';
		break;
	case FTW_SL:
		type = 'S';
		break;
	case FTW_SLN:
		type = 's';
		break;
	default:
		type = '?';
		break;
	}

	printf("[%c] %s\\n", type, path);

	return (0);
}

int
main(int argc, char **argv)
{

	if (argc != 2) {
		printf("Usage %s <directory>\\n", argv[0]);
		return (EX_USAGE);
	} else
		return (nftw(argv[1], nftw_callback, /* UNUSED */ 1, 0));
}
.Ed
.Sh ERRORS
The
.Fn ftw
and
.Fn nftw
functions may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr close 2 ,
.Xr open 2 ,
.Xr stat 2 ,
.Xr malloc 3 ,
.Xr opendir 3
and
.Xr readdir 3 .
If the
.Dv FTW_CHDIR
flag is set, the
.Fn nftw
function may fail and set
.Va errno
for any of the errors specified for
.Xr chdir 2 .
In addition, either function may fail and set
.Va errno
as follows:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa maxfds
argument is less than 1.
.El
.Sh SEE ALSO
.Xr chdir 2 ,
.Xr close 2 ,
.Xr open 2 ,
.Xr stat 2 ,
.Xr fts 3 ,
.Xr malloc 3 ,
.Xr opendir 3 ,
.Xr readdir 3
.Sh STANDARDS
The
.Fn ftw
and
.Fn nftw
functions conform to
.St -p1003.1-2001 .
.Sh HISTORY
These functions first appeared in
.At V.3 .
Their first
.Fx
appearance was in
.Fx 5.3 .
.Sh BUGS
The
.Fa maxfds
argument is currently ignored.