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I want to truncate (cut/shorten) a string that contains newline (\\ or \newline) in such a way that only the first line remains.

My problem is, that I use the todonotes package and have command wrapped around the normal \todo. Here is a minimal working example: (my actual command is more complex)

\newcommand{\TODO}[2]{\todo[#1,inline, caption={#2}]{#2}}

The problem is, that I might call that function with something that contains a newline. This will fail while setting the caption. Also, it is a bad idea to have a multi-line caption. 

 \TODO{foo \\ bar}

Therefore I want to truncate the string first. I tried the xstring package, but I can not find anything on how to do it for newline (\\ or \newline). I could use xstring to cut the string after x characters, but I do not know how soon the \\ will happen.

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  • you haven't provided a test file but I assume caption={\zz#2\\\relax} works were \zz is defined by \def\zz#1\\#2\relax{#1} Commented Jan 28, 2016 at 14:51
  • \let\newline=\relax ? Not sure if that would work on \\ though. Commented Jan 28, 2016 at 15:12

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Assuming that \TODO has an optional argument for specifying possible other options to \todo and a mandatory argument, which you want to truncate only in the list of todos, here's a way:

\documentclass{article} \usepackage{xparse} \usepackage{todonotes} \ExplSyntaxOn \NewDocumentCommand{\TODO}{ O{} m } { \seq_set_split:Nnn \l_tmpa_seq { \\ } { #2 } \masgo_todo:nfn { #1 } { \seq_item:Nn \l_tmpa_seq { 1 } } { #2 } } \cs_new_protected:Nn \masgo_todo:nnn { \todo[inline, caption={#2}, #1]{#3} } \cs_generate_variant:Nn \masgo_todo:nnn { nf } \ExplSyntaxOff \begin{document} \listoftodos \section{Test} First\TODO{x} Second\TODO{x \\ y} Third\TODO{x \\ y \\ z} \end{document}

The mandatory argument is split at \\ and then the first item is used for the caption, while the whole argument is used for the note.

enter image description here

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  • First, let me thank you and second: Why does this work? What magic happens between \ExplSyntaxOn and \ExplSyntaxOff? (And why doesn't Google find anything useful about the commands you use there?) Commented Jan 29, 2016 at 9:31
  • @masgo Essentially, it is “split off the mandatory argument whatever comes from the first \\ and use it for the caption. Doing it with a sequence is not the only way, but, as you see, it just requires very short code and it allows for further modifications: it would be easy to change the \\ into spaces for getting the full caption without line breaks. Commented Jan 29, 2016 at 9:36
  • Can you point me to some resource that explains the commands you use (\seq_set_split:Nnn \l_tmpa_seq \seq_item:Nn \cs_new_protected:Nn \cs_generate_variant:Nn). Google just gives me more stackoverflow answers that use them without explaination. The only thing I could find is \ExplSyntaxOn and the xparse documentation that explains NewDocumentCommand Commented Jan 29, 2016 at 9:49
  • @masgo On your TeX system you should be able to do texdoc interface3 and texdoc xparse (or go to texdoc.net) Commented Jan 29, 2016 at 9:50
  • I found out, that the solution does not work if I have a new paragraph in my todo note (two consecutive new lines leading to a \par .. or simply a \par) .. I tried to change \NewDocumentCommand{\TODO}{ O{} m } to \NewDocumentCommand{\TODO}{ O{} +m } according to the xparse documentation this should make the command also parse paragraphs, but somehow it does not. Commented Feb 17, 2016 at 9:15

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