FileNameSplit

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

FileNameSplit["name"]

splits a file name into a list of parts.

FileNameSplit[..., OperatingSystem->"os"]

uses the conventions of the specified operating system; possible choices are "Windows", "MacOSX", and "Unix".

Notes

FileNameSplit by default uses pathname separators and other conventions suitable for your operating system. Absolute file names that begin with a pathname separator yield a list of parts that starts with "". Under Windows, the drive or share name is treated as the first part of the file name. FileNameSplit just operates on names of files; it does not actually search for the file specified.

Examples (8)

Every input below was run against the current Mathilda build and its output recorded.

Basic Examples (4)

Leading "" marks an absolute path

In[1]:= FileNameSplit["/home/user/data.csv"]
Out[1]= {"", "home", "user", "data.csv"}

Duplicate and trailing separators are dropped

In[2]:= FileNameSplit["a//b/c/"]
Out[2]= {"a", "b", "c"}

Join inverts Split

In[3]:= FileNameJoin[FileNameSplit["/usr/local/bin"]]
Out[3]= "/usr/local/bin"

A drive is an ordinary first part

In[4]:= FileNameSplit["C:\\path\\file.txt", OperatingSystem -> "Windows"]
Out[4]= {"C:", "path", "file.txt"}

Applications (4)

Leading "" marks an absolute path

In[5]:= FileNameSplit["/home/user/data.csv"]
Out[5]= {"", "home", "user", "data.csv"}

Duplicate and trailing separators are dropped

In[6]:= FileNameSplit["a//b/c/"]
Out[6]= {"a", "b", "c"}

Join inverts Split

In[7]:= FileNameJoin[FileNameSplit["/usr/local/bin"]]
Out[7]= "/usr/local/bin"

A drive is an ordinary first part

In[8]:= FileNameSplit["C:\\path\\file.txt", OperatingSystem -> "Windows"]
Out[8]= {"C:", "path", "file.txt"}

Implementation notes

Algorithm. builtin_filenamesplit is the structural inverse of FileNameJoin and, like it, is a pure string operation that never touches the filesystem. It decodes the same trailing OperatingSystem -> "..." option into a windows flag (sharing fnj_is_sep and the absolute/UNC rules), requires a single string spec, and calls fns_split_build.

fns_split_build handles the leading context first: under Windows a \\host\share UNC prefix is captured as one part; otherwise a leading separator (an absolute path) emits a leading "" part. It then consumes the rest as maximal non-separator runs, dropping empty runs from trailing and duplicated separators — so "a//b/c/" splits to {"a","b","c"}. The parts are assembled into a List[...]; a non-string argument or an unknown OS leaves the call unevaluated, and FileNameSplit[] prints FileNameSplit::argx.

Data structures. A char** of freshly-malloc'd part strings (fns_dup copies each substring; an upper bound of strlen(path)+2 parts is allocated once), converted to expr_new_string elements that expr_new_function adopts into the List. A Windows drive like C: contains no separator and so falls out naturally as an ordinary first part.

Complexity / limits. O(path length), single pass. FileNameJoin[FileNameSplit[name]] reconstructs a canonicalized name. ATTR_PROTECTED.

• Protected.
• Pure string operation — does not touch the filesystem.
• A leading pathname separator marks an absolute path and yields a leading "" part; trailing and duplicate separators are dropped ("a//b/" → {"a", "b"}).
• "Windows" treats a leading \\server\share UNC prefix as a single part and a drive like C: as an ordinary first part; "MacOSX"/"Unix" split on /. The default is the host operating system's separator.
• Options[FileNameSplit] reports the OperatingSystem default.
• FileNameJoin[FileNameSplit[name]] reconstructs a canonicalized name.
• FileNameSplit[] prints FileNameSplit::argx and stays unevaluated; a non-string argument or an unknown OS leaves the call unevaluated.

Attributes: Protected.

References

See also: List, FileNameJoin

• Source: src/files.c
• Specification: docs/spec/builtins/file-io.md
• Tests: tests/test_files.c

Notes & additional examples

Notes

FileNameSplit["name"] is the structural inverse of FileNameJoin: it returns the list of path components. It is a pure string operation and never touches the filesystem. A leading separator makes the path absolute and yields a leading "" part; trailing and duplicate separators are dropped.

The separator defaults to the host operating system's; OperatingSystem -> "Windows" | "MacOSX" | "Unix" selects it. On "Windows" a leading UNC \\server\share prefix is kept as a single part and a drive like C: falls out as an ordinary first part. A non-string argument or an unknown OS leaves the call unevaluated.