Turning off text wrapping inside .bbl files

Question

BibTeX does linebreaking on the .bbl files it write outs. How do I turn that off, or adjust it? It is breaking lines inside long URLs with spaces in the bibliography, causing them to stop working.

Here’s is a MWE.

\documentclass{article}
\usepackage[spaces,obeyspaces]{url}
\usepackage{hyperref}
\usepackage{filecontents}
\begin{document}

\begin{filecontents}{foo.bst}

ENTRY {
    url
  }
  {}
  {}

FUNCTION {misc}
{
    "\url{" url "}" * * write$ newline$
    "\par" write$ newline$
}

READ

ITERATE {call.type$}

\end{filecontents}

\begin{filecontents}{foo.bib}
@misc{key1,
    url = "http://example.com"
}

@misc{key2,
    url = "http://example.com/this is a long url that contains more spaces than BibTeX can handle"
}
\end{filecontents}

\nocite{*}

\section{Bibliography}

\bibliographystyle{foo}
\bibliography{foo}

\end{document}

Clicking the first link opens a browser, but the second does not.

Here is a line-numbered version of the .bbl file it spits out:

1 \url{http://example.com}
2 \par
3 \url{http://example.com/this is a long url that contains more spaces than
4   BibTeX can handle}
5 \par

btxhak.pdf claims that “write$ does reasonable line breaking” …

Answer 1

BibTeX is hard-coded to wrap lines after 80 characters where a space occurs (older versions would wrap even without a space, which caused issues with URLs). As is mentioned in a comment, spaces are invalid inside URLs in any case, so they should be converted to %20. The best you can do is write a BibTeX function to deliberately line break at a point of your choosing, but that will depend on what you feel is acceptable.

---

One possible approach here would be to use a search-and-replace function to insert `%20`

\documentclass{article}
\usepackage[spaces,obeyspaces]{url}
\usepackage{hyperref}
\usepackage{filecontents}
\begin{document}

\begin{filecontents}{foo.bst}

ENTRY {
    url
  }
  {}
  {}

FUNCTION { not } 
  { 
      {#0}
      {#1} 
    if$
  }

INTEGERS { l }
FUNCTION { string.length }
  {
    #1 'l :=
      {
        duplicate$
         duplicate$
        #1 l substring$ = not
      }
      { l #1 + 'l := }
    while$
    pop$
    l
  }

STRINGS { replace find text }

INTEGERS { find.length }

FUNCTION { find.replace }
  { 
    'replace :=
    'find :=
    'text :=
    find string.length 'find.length :=
    ""
      { text empty$ not }
      {
        text #1 find.length substring$ find =
        {
          replace *
          text #1 find.length + global.max$ substring$ 'text :=
        }
        { text #1 #1 substring$ *
          text #2 global.max$ substring$ 'text :=
        }
      if$
    }
  while$
}

FUNCTION {misc}
{
    "\url{" url " " "%20" find.replace "}" * * write$ newline$
    "\par" write$ newline$
}

READ

ITERATE {call.type$}

\end{filecontents}

\begin{filecontents}{foo.bib}
@misc{key1,
    url = "http://example.com"
}

@misc{key2,
    url = "http://example.com/this is a long url that contains more spaces than BibTeX can handle"
}
\end{filecontents}

\nocite{*}

\section{Bibliography}

\bibliographystyle{foo}
\bibliography{foo}

\end{document}

using code from Tame the BeaST.