FTS(3)

FTS(3) | Library Functions Manual | FTS(3)

# NAME

`fts`, `fts_open`, `fts_read`, `fts_children`, `fts_set`, `fts_close` — traverse a file hierarchy

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <sys/types.h>`
`#include <sys/stat.h>`
`#include <fts.h>`

FTS *
`fts_open`(char * const *path_argv, int options, int (*compar)(const FTSENT **, const FTSENT **));

FTSENT *
`fts_read`(FTS *ftsp);

FTSENT *
`fts_children`(FTS *ftsp, int options);

int
`fts_set`(FTS *ftsp, FTSENT *f, int options);

int
`fts_close`(FTS *ftsp);

# DESCRIPTION

The `fts` functions are provided for traversing UNIX file hierarchies. A simple overview is that the `fts_open`() function returns a “handle” on a file hierarchy, which is then supplied to the other `fts` functions. The function `fts_read`() returns a pointer to a structure describing one of the files in the file hierarchy. The function `fts_children`() returns a pointer to a linked list of structures, each of which describes one of the files contained in a directory in the hierarchy. In general, directories are visited two distinguishable times; in pre-order (before any of their descendants are visited) and in post-order (after all of their descendants have been visited). Files are visited once. It is possible to walk the hierarchy “logically” (ignoring symbolic links) or physically (visiting symbolic links), order the walk of the hierarchy or prune and/or re-visit portions of the hierarchy.

Two structures are defined (and `typedef`'ed) in the include file `<fts.h>`. The first is FTS, the structure that represents the file hierarchy itself. The second is FTSENT, the structure that represents a file in the file hierarchy. Normally, an FTSENT structure is returned for every file in the file hierarchy. In this manual page, “file” and “FTSENT structure” are generally interchangeable. The FTSENT structure contains at least the following fields, which are described in greater detail below:

    typedef struct _ftsent {
            u_short fts_info;           /* flags for FTSENT structure */
            char *fts_accpath;          /* access path */
            char *fts_path;             /* root path */
            short fts_pathlen;          /* strlen(fts_path) */
            char *fts_name;             /* file name */
            short fts_namelen;          /* strlen(fts_name) */
            short fts_level;            /* depth (-1 to N) */
            int fts_errno;              /* file errno */
            long fts_number;            /* local numeric value */
            void *fts_pointer;          /* local address value */
            struct ftsent *fts_parent;  /* parent directory */
            struct ftsent *fts_link;    /* next file structure */
            struct ftsent *fts_cycle;   /* cycle structure */
            struct stat *fts_statp;     /* stat(2) information */
    } FTSENT;

These fields are defined as follows:

fts_info
  One of the following flags describing the returned FTSENT structure and the file it represents. With the exception of directories without errors (`FTS_D`), all of these entries are terminal, that is, they will not be revisited, nor will any of their descendants be visited.
  `FTS_D`
    A directory being visited in pre-order.
  `FTS_DC`
    A directory that causes a cycle in the tree. The fts_cycle field of the FTSENT structure will be filled in as well.
  `FTS_DEFAULT`
    Any FTSENT structure that represents a file type not explicitly described by one of the other fts_info values.
  `FTS_DNR`
    A directory which cannot be read. This is an error return, and the fts_errno field will be set to indicate what caused the error.
  `FTS_DOT`
    A file named ‘`.`’ or ‘`..`’ which was not specified as a file name to `fts_open`() (see `FTS_SEEDOT`).
  `FTS_DP`
    A directory being visited in post-order. The contents of the FTSENT structure will be unchanged from when it was returned in pre-order, i.e., with the fts_info field set to `FTS_D`.
  `FTS_ERR`
    This is an error return, and the fts_errno field will be set to indicate what caused the error.
  `FTS_F`
    A regular file.
  `FTS_NS`
    A file for which no stat(2) information was available. The contents of the fts_statp field are undefined. This is an error return, and the fts_errno field will be set to indicate what caused the error.
  `FTS_NSOK`
    A file for which no stat(2) information was requested. The contents of the fts_statp field are undefined.
  `FTS_SL`
    A symbolic link.
  `FTS_SLNONE`
    A symbolic link with a non-existent target. The contents of the fts_statp field reference the file characteristic information for the symbolic link itself.
  `FTS_W`
    A whiteout object.
fts_accpath
  A path for accessing the file from the current directory.
fts_path
  The path for the file relative to the root of the traversal. This path contains the path specified to `fts_open`() as a prefix.
fts_pathlen
  The length of the string referenced by fts_path.
fts_name
  The name of the file.
fts_namelen
  The length of the string referenced by fts_name.
fts_level
  The depth of the traversal, numbered from -1 to N, where this file was found. The FTSENT structure representing the parent of the starting point (or root) of the traversal is numbered -1, and the FTSENT structure for the root itself is numbered 0.
fts_errno
  Upon return of a FTSENT structure from the `fts_children`() or `fts_read`() functions, with its fts_info field set to `FTS_DNR`, `FTS_ERR` or `FTS_NS`, the fts_errno field contains the value of the external variable errno specifying the cause of the error. Otherwise, the contents of the fts_errno field are undefined.
fts_number
  This field is provided for the use of the application program and is not modified by the `fts` functions. It is initialized to 0.
fts_pointer
  This field is provided for the use of the application program and is not modified by the `fts` functions. It is initialized to `NULL`.
fts_parent
  A pointer to the FTSENT structure referencing the file in the hierarchy immediately above the current file, i.e., the directory of which this file is a member. A parent structure for the initial entry point is provided as well, however, only the fts_level, fts_number and fts_pointer fields are guaranteed to be initialized.
fts_link
  Upon return from the `fts_children`() function, the fts_link field points to the next structure in the `NULL`-terminated linked list of directory members. Otherwise, the contents of the fts_link field are undefined.
fts_cycle
  If a directory causes a cycle in the hierarchy (see `FTS_DC`), either because of a hard link between two directories, or a symbolic link pointing to a directory, the fts_cycle field of the structure will point to the FTSENT structure in the hierarchy that references the same file as the current FTSENT structure. Otherwise, the contents of the fts_cycle field are undefined.
fts_statp
  A pointer to stat(2) information for the file.

A single buffer is used for all of the paths of all of the files in the file hierarchy. Therefore, the fts_path and fts_accpath fields are guaranteed to be NUL-terminated only for the file most recently returned by `fts_read`(). To use these fields to reference any files represented by other FTSENT structures will require that the path buffer be modified using the information contained in that FTSENT structure's fts_pathlen field. Any such modifications should be undone before further calls to `fts_read`() are attempted. The fts_name field is always NUL-terminated.

## FTS_OPEN

The `fts_open`() function takes a pointer to an array of character pointers naming one or more paths which make up a logical file hierarchy to be traversed. The array must be terminated by a `NULL` pointer.

There are a number of options, at least one of which (either `FTS_LOGICAL` or `FTS_PHYSICAL`) must be specified. The options are selected by or'ing the following values:

`FTS_COMFOLLOW`
  This option causes any symbolic link specified as a root path to be followed immediately whether or not `FTS_LOGICAL` is also specified.
`FTS_LOGICAL`
  This option causes the `fts` routines to return FTSENT structures for the targets of symbolic links instead of the symbolic links themselves. If this option is set, the only symbolic links for which FTSENT structures are returned to the application are those referencing non-existent files. Either `FTS_LOGICAL` or `FTS_PHYSICAL` must be provided to the `fts_open`() function.
`FTS_NOCHDIR`
  As a performance optimization, the `fts` functions change directories as they walk the file hierarchy. This has the side-effect that an application cannot rely on being in any particular directory during the traversal. The `FTS_NOCHDIR` option turns off this optimization, and the `fts` functions will not change the current directory. Note that applications should not themselves change their current directory and try to access files unless `FTS_NOCHDIR` is specified and absolute pathnames were provided as arguments to `fts_open`().
`FTS_NOSTAT`
  By default, returned FTSENT structures reference file characteristic information (the fts_statp field) for each file visited. This option relaxes that requirement as a performance optimization, allowing the `fts` functions to set the fts_info field to `FTS_NSOK` and leave the contents of the fts_statp field undefined.
`FTS_PHYSICAL`
  This option causes the `fts` routines to return FTSENT structures for symbolic links themselves instead of the target files they point to. If this option is set, FTSENT structures for all symbolic links in the hierarchy are returned to the application. Either `FTS_LOGICAL` or `FTS_PHYSICAL` must be provided to the `fts_open`() function.
`FTS_SEEDOT`
  By default, unless they are specified as path arguments to `fts_open`(), any files named ‘`.`’ or ‘`..`’ encountered in the file hierarchy are ignored. This option causes the `fts` routines to return FTSENT structures for them.
`FTS_WHITEOUT`
  Return whiteout entries, which are normally hidden.
`FTS_XDEV`
  This option prevents `fts` from descending into directories that have a different device number than the file from which the descent began.

The argument `compar`() specifies a user-defined function which may be used to order the traversal of the hierarchy. It takes two pointers to pointers to FTSENT structures as arguments and should return a negative value, zero, or a positive value to indicate if the file referenced by its first argument comes before, in any order with respect to, or after, the file referenced by its second argument. The fts_accpath, fts_path and fts_pathlen fields of the FTSENT structures may never be used in this comparison. If the fts_info field is set to `FTS_NS` or `FTS_NSOK`, the fts_statp field may not either. If the `compar`() argument is `NULL`, the directory traversal order is in the order listed in path_argv for the root paths, and in the order listed in the directory for everything else.

If an error occurs, `fts_open`() returns `NULL` and sets errno appropriately.

## FTS_READ

The `fts_read`() function returns a pointer to an FTSENT structure describing a file in the hierarchy. Directories (that are readable and do not cause cycles) are visited at least twice, once in pre-order and once in post-order. All other files are visited at least once. (Hard links between directories that do not cause cycles or symbolic links to symbolic links may cause files to be visited more than once, or directories more than twice).

If all the members of the hierarchy have been returned, `fts_read`() returns `NULL` and sets the external variable errno to 0. If an error unrelated to a file in the hierarchy occurs, `fts_read`() returns `NULL` and sets errno appropriately. If an error related to a returned file occurs, a pointer to an FTSENT structure is returned, and errno may or may not have been set (see fts_info).

The FTSENT structures returned by `fts_read`() may be overwritten after a call to `fts_close`() on the same file hierarchy stream, or, after a call to `fts_read`() on the same file hierarchy stream unless they represent a file of type directory, in which case they will not be overwritten until after a call to `fts_read`() after the FTSENT structure has been returned by the function `fts_read`() in post-order.

## FTS_CHILDREN

The `fts_children`() function returns a pointer to an FTSENT structure describing the first entry in a `NULL`-terminated linked list of the files in the directory represented by the FTSENT structure most recently returned by `fts_read`(). The list is linked through the fts_link field of the FTSENT structure, and is ordered by the user-specified comparison function, if any. Repeated calls to `fts_children`() will recreate this linked list.

As a special case, if `fts_read`() has not yet been called for a hierarchy, `fts_children`() will return a pointer to the files in the logical directory specified to `fts_open`(), i.e., the arguments specified to `fts_open`(). Otherwise, if the FTSENT structure most recently returned by `fts_read`() is not a directory being visited in pre-order, or the directory does not contain any files, `fts_children`() returns `NULL` and sets errno to zero. If an error occurs, `fts_children`() returns `NULL` and sets errno appropriately.

The FTSENT structures returned by `fts_children`() may be overwritten after a call to `fts_children`(), `fts_close`() or `fts_read`() on the same file hierarchy stream.

Option may be set to the following value:

`FTS_NAMEONLY`
  Only the names of the files are needed. The contents of all the fields in the returned linked list of structures are undefined with the exception of the fts_name and fts_namelen fields.

## FTS_SET

The function `fts_set`() allows the user application to determine further processing for the file f of the stream ftsp. The `fts_set`() function returns 0 on success, and -1 if an error occurs. Option must be set to one of the following values:

`FTS_AGAIN`
  Re-visit the file; any file type may be re-visited. The next call to `fts_read`() will return the referenced file. The fts_stat and fts_info fields of the structure will be reinitialized at that time, but no other fields will have been changed. This option is meaningful only for the most recently returned file from `fts_read`(). Normal use is for post-order directory visits, where it causes the directory to be re-visited (in both pre- and post-order) as well as all of its descendants.
`FTS_FOLLOW`
  The referenced file must be a symbolic link. If the referenced file is the one most recently returned by `fts_read`(), the next call to `fts_read`() returns the file with the fts_info and fts_statp fields reinitialized to reflect the target of the symbolic link instead of the symbolic link itself. If the file is one of those most recently returned by `fts_children`(), the fts_info and fts_statp fields of the structure, when returned by `fts_read`(), will reflect the target of the symbolic link instead of the symbolic link itself. In either case, if the target of the symbolic link does not exist the fields of the returned structure will be unchanged and the fts_info field will be set to `FTS_SLNONE`.

  If the target of the link is a directory, the pre-order return, followed by the return of all of its descendants, followed by a post-order return, is done.

`FTS_SKIP`
  No descendants of this file are visited. The file may be one of those most recently returned by either `fts_children`() or `fts_read`().

## FTS_CLOSE

The `fts_close`() function closes a file hierarchy stream ftsp and restores the current directory to the directory from which `fts_open`() was called to open ftsp. The `fts_close`() function returns 0 on success, and -1 if an error occurs.

# ERRORS

The function `fts_open`() may fail and set errno for any of the errors specified for the library functions open(2) and malloc(3).

The function `fts_close`() may fail and set errno for any of the errors specified for the library functions chdir(2) and close(2).

The functions `fts_read`() and `fts_children`() may fail and set errno for any of the errors specified for the library functions chdir(2), malloc(3), opendir(3), readdir(3) and stat(2).

In addition, `fts_children`(), `fts_open`() and `fts_set`() may fail and set errno as follows:

[`EINVAL`]
  The options were invalid.

# SEE ALSO

find(1), chdir(2), stat(2), qsort(3), symlink(7)

# STANDARDS

The `fts` utility was expected to be included in the IEEE Std 1003.1-1988 (“POSIX.1”) revision. But twenty years later, it still was not included in the IEEE Std 1003.1-2008 (“POSIX.1”) revision.

October 27, 2024 | NetBSD 11.0