Equivalent of __FILE__?

Question

Many languages define a special identifier whose value is the path to the source file currently being processed. (For example, in C, this is done through the __FILE__ preprocessor macro.)

Does Mathematica have anything like this (at least for *.m files)?

(I could not find a tag that adequately represents the topic of this question (namely, something like "source file processing"); suggestions welcome.)

Answer 1

Just to get an answer on record.

As bobknight stated in the comments $InputFileName is bound to a string giving the full path name of the file being read when code loading operations initiated by Get, (<<), or Needs are in the process of loading. The file being loaded can make use this information, but the notebook requesting the load cannot (think of it as if $InputFileName were bound to the path-name inside a Block, which may actually be the case).

$Input is a system variable that works similarly to $InputFileName but only gives the file name.

Correction

$Inputis a system variable that works similarly to $InputFileName, but is bound to name of the stream from which the loading file is being read. See my additional answer for more detail.

Answer 2

Some additional details on $Input. The Mathematica documentation states that $Input is bound to the name of the stream from which the loading file is being read. But what is that stream name? It appears to be whatever string Get, (<<), or Needs receive as their first argument.

To test this hypothesis, I made a .m file with the following contents and placed in on my system's desktop.

---

Print[Streams[]]
Print[Row[{"$Input: ", $Input}]]
Print[Row[{"$InputFileNamw: ", $InputFileName}]]

---

I then evaluated the following expressions from an open notebook:

Get[SystemDialogInput["FileOpen", "*.m"]]

{OutputStream[stdout, 1], OutputStream[stderr, 2], InputStream[/Users/oldmg/Desktop/TestPkg.m, 86]}
\$Input: /Users/oldmg/Desktop/TestPkg.m
\$InputFileName: /Users/oldmg/Desktop/TestPkg.m

SetDirectory[FileNameJoin[{HomeDirectory[], "Desktop"}]];
Get["TestPkg.m"]

{OutputStream[stdout, 1], OutputStream[stderr, 2], InputStream[TestPkg.m, 118]}
\$Input: TestPkg.m
\$InputFileName: /Users/oldmg/Desktop/TestPkg.m

Note in the first case, $Input and $InputFileName are bound to the same string. This is because SystemDialogInput returns a full path name. In the second case, however, $Input is bound to a string giving only the file name because that is all that was passed to it.