Cfrgtkky

The documentation of tikz gives following example containing the verb command in the node text (Section 2.21 Adding Text, v3):

begin{tikzpicture}

draw (0,0) rectangle (2,2);

draw (0.5,0.5) node [fill=yellow!80!black]

                       {Text at verb!node 1!}

     -- (1.5,1.5) node {Text at verb!node 2!};

end{tikzpicture}

If I want to use the label or pin functionality for nodes, it does not work as expected:

documentclass[tikz]{standalone}

begin{document}

begin{tikzpicture}

draw (0,0) rectangle (2,2);

draw (0.5,0.5) node [fill=yellow!80!black]

                       {Text at verb!a_b!}

                     -- (1.5,1.5) node[label={verb!a_b!}] {Text at verb!a_b!};

end{tikzpicture}

end{document}

The error message given is ! Missing $ inserted. due to the _ I want to use.

documentclass[tikz]{standalone}

usepackage{fancyvrb} DefineShortVerb{|}

begin{document}

SaveVerb{Verb}|a_b|

begin{tikzpicture}

    draw (0,0) rectangle (2,2);

    draw (0.5,0.5) node [fill=yellow!80!black]{Text at |a_b|} -- (1.5,1.5) 

                    node[label=UseVerb{Verb}] {Text at |a_b|};

end{tikzpicture}

end{document}

I really do not fully understand what's going on but I can offer a workaround. To this end, let me first mention that creating a new savebox and trying it to fill with saveboxverbox{verb!a_b!} fails. However, a lrbox works, so I propose to store the content of the label in a savebox first and then use it.

documentclass[tikz]{standalone}

newsaveboxverbox

begin{document}

begin{lrbox}{verbox}

verb!a_b!

end{lrbox}

% fails:

%saveboxverbox{verb!a_b!}

begin{tikzpicture}

draw (0,0) rectangle (2,2);

draw (0.5,0.5) node [fill=yellow!80!black]

                       {Text at verb!a_b!}

                     -- (1.5,1.5) node[label={useboxverbox}] {Text at verb!a_b!};

end{tikzpicture}

end{document}

Another workaround producing same output as in @marmot answer.

documentclass[tikz]{standalone}

begin{document}

begin{tikzpicture}

draw (0,0) rectangle (2,2);

draw (0.5,0.5) node [fill=yellow!80!black]

                       {Text at verb!a_b!}

                     -- (1.5,1.5) node[label=texttt{astring_b}] {Text at verb!a_b!};

end{tikzpicture}

end{document}