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Within a custom command, I'm doing the following to write to a file:

\newcommand\mycommand[1]{ \newwrite\file \immediate\openout\file=foobar.tex \immediate\write\file{ foo bar #1 blarg } \immediate\closeout\file }

Of course when I invoke it as \mycommand{baz}, I get the following contents in foobar.tex:

foo bar baz blarg

with all new lines turned into spaces by LaTeX. My question is, is there a way to output these lines into the file "as expected", i.e. with real new lines at the end of each line instead of a space? I'm thinking some \catcode wizardry should do the trick, but I'm not sure which character I need to redefine and to what category code.

Update

The solution in cmhughes' answer works perfectly. The only problem is when #1 contains embedded newlines. I can of course send it to mycommand with its own slew of ^^J, I was wondering if there is a way to avoid this.

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  • you could use ^^J Commented Jan 5, 2014 at 1:52
  • @cmhughes that looks like an answer to me:-) Commented Jan 5, 2014 at 2:20

2 Answers 2

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I assume you're missing a \newcommand before \mycommand and a [1] after it.

First of all, it should be, at least,

\newwrite\file \newcommand\mycommand[1]{ \immediate\openout\file=foobar.tex \immediate\write\file{ foo bar #1 blarg } \immediate\closeout\file }

or every call to \mycommand would allocate a new output stream. Now, let's see how to cope with the newlines. As others have observed, ^^J is set as the \newlinechar in LaTeX, so we can use it. But, if you want that a write respects new lines also in calls such as

\mycommand{a b c}

you have to work harder. Here's a possibility, by changing the category code of ^^M:

%\newlinechar`^^J % LaTeX already does this \newwrite\file \def\mycommand{\begingroup\obeylines\mycommandaux} \begingroup\obeylines \gdef\mycommandaux#1{% \obeylines% \def^^M{^^J}% \immediate\openout\file=foobar.tex% \immediate\write\file{% foo bar #1 blarg% <- no new line at the end }% \immediate\closeout\file% \endgroup% } \endgroup \mycommand{a b c}

Here's the contents of foobar.tex

foo bar a b c blarg

There is an obvious limitation: \mycommand cannot be an argument to another command.

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  • "I assume..." D'oh! Sorry, I posted the question at 3 AM after a long day. Thanks for the answer: it's exactly what I was looking for. Every day I see more value to learning the TeX internals... Commented Jan 5, 2014 at 15:23
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You can use ^^J as follows

\mycommand{% \newwrite\file \immediate\openout\file=foobar.tex \immediate\write\file{% foo^^J% bar^^J% #1^^J% blarg^^J% }% \immediate\closeout\file% }%
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  • +1 This works and I have tried it already. Sorry I failed to mention this. The problem is when #1 itself has newlines. I'll update my question to reflect this info. Commented Jan 5, 2014 at 11:21
  • Sorry, I had to accept egreg's answer as it does exactly what I want. My bad for failing to be more specific earlier. Commented Jan 5, 2014 at 15:24
  • Is it also possible to write space using that way somehow? Commented Apr 19, 2017 at 0:28

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