March 31, 2004 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

```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'd) 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 ```NULL`-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 ```NULL`-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 ```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 ```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.

### 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 is expected to be included in a future IEEE Std 1003.1-1988 (``POSIX.1'') revision.