# fts

## 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_**,**
                         **typeof(int (const FTSENT **, const FTSENT **))**
                             ***_Nullable** _compar_**);**
    
           **FTSENT *fts_read(FTS ***_ftsp_**);**
    
           **FTSENT *fts_children(FTS ***_ftsp_**, int** _instr_**);**
    
           **int fts_set(FTS ***_ftsp_**, FTSENT ***_f_**, int** _instr_**);**
    
           **int fts_close(FTS ***_ftsp_**);**
    


## DESCRIPTION



           The fts functions are provided for traversing file hierarchies.  A
           simple overview is that the **fts_open**() function returns a "handle"
           (of type _FTS *_) that refers to a file hierarchy "stream".  This
           handle 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
           preorder (before any of their descendants are visited) and in
           postorder (after all of their descendants have been visited).
           Files are visited once.  It is possible to walk the hierarchy
           "logically" (visiting the files that symbolic links point to) or
           physically (visiting the symbolic links themselves), order the
           walk of the hierarchy or prune and/or revisit portions of the
           hierarchy.
    
           Two structures (and associated types) are defined in the include
           file _< fts.h>_.  The first type is _FTS_ , the structure that
           represents the file hierarchy itself.  The second type 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 fields describing a file.  The
           structure contains at least the following fields (there are
           additional fields that should be considered private to the
           implementation):
    
               typedef struct _ftsent {
                   unsigned short  fts_info;     /* flags for FTSENT structure */
                   char           *fts_accpath;  /* access path */
                   char           *fts_path;     /* root path */
                   short           fts_pathlen;  /* strlen(fts_path) +
                                                    strlen(fts_name) */
                   char           *fts_name;     /* filename */
                   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;    /* [l]stat(2) information */
               } FTSENT;
    
           These fields are defined as follows:
    
           _fts_info_
                  One of the following values 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 preorder.
    
                  **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 filename to **fts_open**() (see **FTS_SEEDOT**).
    
                  **FTS_DP** A directory being visited in postorder.  The
                         contents of the _FTSENT_ structure will be unchanged
                         from when it was returned in preorder, that is, 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 [**l**]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 [**l**]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 nonexistent target.  The
                         contents of the _fts_statp_ field reference the file
                         characteristic information for the symbolic link
                         itself.
    
           _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 sum of the lengths of the strings referenced by
                  _fts_path_ and _fts_name_.
    
           _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_
                  If **fts_children**() or **fts_read**() returns an _FTSENT_ structure
                  whose _fts_info_ field is set to **FTS_DNR** , **FTS_ERR** , or **FTS_NS** ,
                  the _fts_errno_ field contains the error number (i.e., the
                  _errno_ value) specifying 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, that is,
                  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 [**l**]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 ORing the following values:
    
           **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 nonexistent files:
                  the _fts_statp_ field is obtained via stat(2) with a fallback
                  to lstat(2).
    
           **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: the _fts_statp_ field is
                  obtained via lstat(2).
    
           **FTS_COMFOLLOW**
                  This option causes any symbolic link specified as a root
                  path to be followed immediately, as if via **FTS_LOGICAL** ,
                  regardless of the primary mode.
    
           **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.  This 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_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_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 preorder and once in postorder.  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 _errno_ to 0.  If an error unrelated to a file
           in the hierarchy occurs, **fts_read**() returns NULL and sets _errno_ to
           indicate the error.  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
           postorder.
    
       **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 re-create 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**(), that is, the
           arguments specified to **fts_open**().  Otherwise, if the _FTSENT_
           structure most recently returned by **fts_read**() is not a directory
           being visited in preorder, 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_ to
           indicate the error.
    
           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.
    
           The _instr_ argument is either zero or 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.
    
           The _instr_ argument is either 0 (meaning "do nothing") or one of
           the following values:
    
           **FTS_AGAIN**
                  Revisit the file; any file type may be revisited.  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
                  postorder directory visits, where it causes the directory
                  to be revisited (in both preorder and postorder) 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 preorder
                  return, followed by the return of all of its descendants,
                  followed by a postorder 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 the file hierarchy stream referred
           to by _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 open(2) and malloc(3).
    
           In addition, **fts_open**() may fail and set _errno_ as follows:
    
           **ENOENT** Any element of _path_argv_ was an empty string.
    
           The function **fts_close**() may fail and set _errno_ for any of the
           errors specified for chdir(2) and close(2).
    
           The functions **fts_read**() and **fts_children**() may fail and set _errno_
           for any of the errors specified for chdir(2), malloc(3),
           opendir(3), readdir(3), and [**l**]stat(2).
    
           In addition, **fts_children**(), **fts_open**(), and **fts_set**() may fail
           and set _errno_ as follows:
    
           **EINVAL** _options_ or _instr_ was invalid.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌────────────────────────────────────┬───────────────┬───────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├────────────────────────────────────┼───────────────┼───────────┤
           │ **fts_open**(), **fts_set**(), **fts_close**() │ Thread safety │ MT-Safe   │
           ├────────────────────────────────────┼───────────────┼───────────┤
           │ **fts_read**(), **fts_children**()         │ Thread safety │ MT-Unsafe │
           └────────────────────────────────────┴───────────────┴───────────┘
    


## STANDARDS



           None.
    


## BUGS



           Before glibc 2.23, all of the APIs described in this man page are
           not safe when compiling a program using the LFS APIs (e.g., when
           compiling with _-D_FILE_OFFSET_BITS=64_).
    


* * *