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I recently wanted to use FilePrint to print the contents somewhere else but in the notebook I was using. However, the obvious-seeming solution doesn't work at all:

In[137]:= temp = With[{str = OpenWrite[]},
             Block[{$Output = str},
              Print["fee fi fo fum"]];

In[138]:= FilePrint[temp]
          "fee fi fo fum"

In[139]:= With[{str=OpenWrite[]},
           Block[{$Output = str},
          "fee fi fo fum"

Since the obvious solution doesn't work, does anybody know a less obvious solution, preferably one that doesn't involve re-implementing FilePrint myself? Sure, that would be easy, but I'd prefer not to do it.

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I didn't find an easy solution ... but why don't you just use CopyFile[] ? – Dr. belisarius Mar 31 '12 at 20:22
up vote 4 down vote accepted

I can only give a partial answer. Your problem arises because FilePrint doesn't use $Output (stdout). It uses the stderr stream, so you can't capture what it writes by using Block and assigning to $Output. Unfortunately, I don't think any system variable is bound to stderr. Perhaps I'm wrong. In that case, I hope a more knowable person will be able to complete this answer.

In case anyone is interested, here is how I discovered that FilePrint was using stderr.

text = "fee fi fo fum";
output = With[{str = OpenWrite[]},
  Block[{$Output = str},
FilePrint[Print[Streams[]]; output]


"fee fi fo fum"
share|improve this answer
You shouldn't use LaTeX to do code formatting; LaTeX is there for formulas. Code formatting is done by simply indenting the code by four spaces. To code-format small snippets embedded in the text (like FilePrint or $Output), enclose the snippet in backquotes. – celtschk Oct 15 '12 at 12:27
@celtschk Thanks for the formatting tips. I've edited the post using your advice. – m_goldberg Oct 15 '12 at 12:57

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