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How to send output of Information[] command to a text file?


I am having little hard time sending output of Information[] command to a text file.


related question How to write output to an external text file in addition to the standard output stream?


I'd like to find what is the correct way to do this. I tried the following 3 things, including what is in the above link, but nothing worked for me. I am using version 8.0.4 on windows 7.


s = OpenWrite["test.txt", FormatType -> OutputForm] (*without FormatType also error*)
$Post = Write[#, s] &

Information["DSolve", LongForm -> False]
Close[s]
$Post =.

second attempt


s = OpenWrite["test.txt"]
$Output = s
Information["DSolve", LongForm -> False]
Close[s]


Third attempt (using the same solution given in the above link)


output = OpenWrite["out.txt", FormatType -> OutputForm];
$PrePrint = (Write[output, #]; #) &;
Information["DSolve", LongForm -> False]

I see the file out.txt gets created, but it is empty. Nothing is written to it. Even after I close Mathematica or the kernel, it is empty. I also get an error when I close it


Close[output]  (*Write::noopen: "Cannot open OutputStream["out.txt",19]"*)

Basically, I want to issue many commands in my notebook, in the form of Information[...] for many topics, and I want this otuput to go to a text file to process later.


What would be the right way to do this?



thanks,


edit


fyi, this is the final version. A small example, to show how it is now working: (this is part of a larger code I use to generate all the symbols in all packages in Mathematica). I was cleaning it to get ready to run it when V 9 is out.


Get["Utilities`CleanSlate`"]
SetOptions[CleanSlate, Verbose -> False];
addOnPackages = {"ANOVA", "Audio"};
output = OpenWrite["info.txt", FormatType -> OutputForm, PageWidth -> Infinity];
$Output = output;
$Urgent = output;


Do[{
packageName = addOnPackages[[i]];
Print["<", packageName];
Get[packageName <> "`"];
funs = Names[packageName <> "`*"];
Information[#, LongForm -> False] & /@ funs;
CleanSlate[Evaluate[packageName <> "`"]]
}, {i, 1, Length[addOnPackages]}
];


Close[output];

Thanks for Todd and Mike help in this.


update 12/1/2012


FYI,


Based on what I learned from the replies here, I made this little function that allows one to capture the output from ? on command into a string. (if you want ?? output, then just change the LongForm->False to LongForm->True (will update this function later to add this as an option to the call. But for now, just to give an idea)


help[fun_String] := Module[{s, file},
SetDirectory[NotebookDirectory[]];
file = OpenWrite["s.txt", FormatType -> OutputForm, PageWidth -> Infinity];
Block[{$Urgent = file},

Information[fun, LongForm -> False] ];
Close[file];
Import["s.txt"]
]

To use it


s = help["DSolve"];

and now s is a string of what would have gone to screen.



Answer




The output from Information[] gets sent to the $Urgent stream. Here is how you can capture it:


infoFile = OpenWrite["info.txt", FormatType -> OutputForm, PageWidth -> Infinity]

Block[{$Urgent = infoFile},
Information["DSolve", LongForm -> False]
]

Close[infoFile]

Note that I used PageWidth->Infinity. This results in possibly (?) cleaner formatting in the file. It depends on how you want to process it.



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