I can not figure out why the code below doesn't work?

aaa >> FileNameJoin[{Directory[],"input"}]

error message came out saying

OpenWrite::noopen: Cannot open FileNameJoin[{Directory[],"input"}].

If I evaluate


directly, then I can get


And the code below always works

aaa >> "C:\\Users\\m&p\\AppData\\Local\\Temp\\input"
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    $\begingroup$ did you type this in a notebook? what is aaa >> ? Did you check to see if you have a file called ` FileNameJoin[{Directory[],"input"}]` ? i.e. evaluate ` FileNameJoin[{Directory[],"input"}]` and see what it says, then go see if that file exist. btw, you code says "input" but the message you show says "input2" $\endgroup$ – Nasser Nov 10 '13 at 5:38
  • $\begingroup$ @Nasser I've edited my question. aaa can be anything just for convenience. If I didn't define aaa, the aaa>>file will put 3 "a" characters into file . $\endgroup$ – matheorem Nov 10 '13 at 7:00
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    $\begingroup$ @Nasser and it shouldn't be a matter if there is already a file with the name "input" exit? Put always write, I think $\endgroup$ – matheorem Nov 10 '13 at 7:02
  • $\begingroup$ It works fine for me, "test" >> FileNameJoin[{Directory[], "input"}] no errors, and the file is created fine as C:\Users\me\Documents\input and I opened the file with text editor and it has "test" in it. Windows 7, M V 9.01. It might be the space you have there in the folder path? what is that & you show there in the name? $\endgroup$ – Nasser Nov 10 '13 at 7:11
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    $\begingroup$ This question is almost a duplicate of "Infix form of PutAppend ( >>> ) does not work with variable" and a duplicate of "Using a variable in Get." $\endgroup$ – Alexey Popkov Nov 10 '13 at 8:17

Mathematica 9.0, WinXP

Apparently both forms of Put[] (ie Put[] and >>) don't operate with the same criteria on the file name treatment. Please take a look at the syntax coloring in the following example:

Mathematica graphics

While the standard Put[] waits for an expression to be interpreted, the >> form waits for a String (with or without apostrophes).

So, when you enter

aaa >> FileNameJoin[{Directory[],"input"}]

it tries to write to a file whose name is literally "FileNameJoi ..." etc. and fails.

It can be circumvented by entering

aaa >> (FileNameJoin[{Directory[], "input"}])

-- Very curious, BTW.

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    $\begingroup$ I would call it "a bug by design" $\endgroup$ – Dr. belisarius Nov 10 '13 at 7:26
  • $\begingroup$ WOW! That is the point! I just noticed the important small space before I came back and look at your answer. This is absolutely a "bug" I think $\endgroup$ – matheorem Nov 10 '13 at 7:32
  • $\begingroup$ But it works on my system without (): !Mathematica graphics no errors. $\endgroup$ – Nasser Nov 10 '13 at 7:33
  • $\begingroup$ @Nasser the small space is the key. between "," and "input". (,"input") will be wrong, (, "input") will be right $\endgroup$ – matheorem Nov 10 '13 at 7:33
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    $\begingroup$ Reminds me of this question $\endgroup$ – cormullion Nov 10 '13 at 8:01

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