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FileExtension

Status: Stable

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

Description

FileExtension["file"]

gives the file extension for a file name.

FileExtension["name.ext"] gives "ext".

Notes FileExtension gives the extension that appears after the last . in a file name. If there are multiple endings to a file name, separated by ., FileExtension gives only the last one. FileExtension gives "" if there is no file extension, if the file name has the form of a directory name, or ends with a . character. FileExtension ignores any directory specification. FileExtension by default assumes pathname separators and other conventions suitable for your operating system.

Examples (2)

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

Applications (2)

In[1]:= FileExtension["report.txt"]
Out[1]= "txt"

In[2]:= FileExtension["/tmp/data/report.txt"]
Out[2]= "txt"

Implementation notes

builtin_fileextension is pure string manipulation (no filesystem access). It isolates the filename component (after the last /, via filename_component) and finds the extension start with extension_offset: the offset just past the last . that is neither the first nor the last character of the component (so .bashrc and file. have no extension). It returns the substring from that offset — i.e. the suffix without the dot — as an EXPR_STRING, or "" when there is no extension. ATTR_PROTECTED.

  • Protected.
  • Pure string operation — does not touch the filesystem.
  • Returns "" when the leaf has no extension, when it ends with ., when the leaf has only a leading . (e.g. ".bashrc"), or when the path has the form of a directory (ends with /).
  • Always ignores everything up to and including the final /.

Attributes: Protected.

References

Notes & additional examples

Notes

FileExtension returns the extension (without the dot), taken after the final dot in the file name.