I want to use a macro in \write18, but this causes the space after it to be ignored. The following example prints foobar to test.txt, whereas I want it to print foo bar:

\write18{echo \foo bar > test.txt}

I tried {\foo}, \foo{}, and \foo\ instead of just \foo, but these all print the braces and slashes to the file, which is not what I want. How can I expand the macro without introducing extra characters, and without removing the space?

The example above is of course simplified. In my real scenario, I am not able to modify the \foo command, though I could define a wrapper.

  • 1
    \foo\space bar maybe? – clemens Jun 27 '15 at 15:26
  • Yep, \space is what I needed. – Ruud Jun 27 '15 at 15:33

You want \space instead of or instead of the braces. Braces are unexpandable tokens which means they're not removed in \write18. is an unexpandable primitive which again means it is not removed (or rather: expanded) in \write18. \space on the other hand is an expandable macro which expands to a space.



\edef\test{\foo\ bar}

\edef\test{\foo{} bar}

\edef\test{\foo\space bar}


The log entry:

> \test=macro:
->foo\ bar.
l.7 \show\test

> \test=macro:
->foo{} bar.
l.10 \show\test

> \test=macro:
->foo bar.
l.13 \show\test

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