URL line breaks with biblatex

Question

How do I allow long URLs to have line breaks at any point. This is in the bibliography not the main text. I am trying to save space so don't want extra spaces to be added to make it only break at slashes, for example, as it does by default. I am using biblatex+biber.

Answer 1

Answers to the question linked in domwass's comment mention the package url. This package is already loaded by biblatex. It is configured with the command \biburlsetup defined in biblatex.def.

URLs are broken at the set of characters specified in \UrlBreaks, \UrlBigBreaks and \UrlSpecials. \UrlBigBreaks will prevent breaks from occurring between repeating characters (e.g. -- and :: in the code below). \UrlSpecials handles breaks at characters that may not be present in the document font.

Upgrading to the latest version of biblatex should solve your problem as \biburlsetup was expanded in version 1.4c to permit breakpoints at many different characters. For reference here is the definition for \biburlsetup from version 1.7:

\newcounter{biburlnumpenalty}
\newcounter{biburlucpenalty}
\newcounter{biburllcpenalty}

\newcommand*{\biburlsetup}{%
  \Urlmuskip=0mu plus 3mu\relax
  \mathchardef\UrlBigBreakPenalty=100\relax
  \mathchardef\UrlBreakPenalty=200\relax
  \def\UrlBigBreaks{\do\:\do\-}%
  \def\UrlBreaks{%
    \do\.\do\@\do\/\do\\\do\!\do\_\do\|\do\;\do\>\do\]\do\)\do\}%
    \do\,\do\?\do\'\do\+\do\=\do\#\do\$\do\&\do\*\do\^\do\"}%
  \ifnumgreater{\value{biburlnumpenalty}}{0}
    {\def\do##1{\appto\UrlSpecials{\do##1{\mathchar`##1 \penalty\value{biburlnumpenalty}}}}%
     \do\1\do\2\do\3\do\4\do\5\do\6\do\7\do\8\do\9\do\0}
    {}%
  \ifnumgreater{\value{biburlucpenalty}}{0}
    {\def\do##1{\appto\UrlSpecials{\do##1{\mathchar`##1 \penalty\value{biburlucpenalty}}}}%
     \do\A\do\B\do\C\do\D\do\E\do\F\do\G\do\H\do\I\do\J
     \do\K\do\L\do\M\do\N\do\O\do\P\do\Q\do\R\do\S\do\T
     \do\U\do\V\do\W\do\X\do\Y\do\Z}
    {}%
  \ifnumgreater{\value{biburllcpenalty}}{0}
    {\def\do##1{\appto\UrlSpecials{\do##1{\mathchar`##1 \penalty\value{biburllcpenalty}}}}%
     \do\a\do\b\do\c\do\d\do\e\do\f\do\g\do\h\do\i\do\j
     \do\k\do\l\do\m\do\n\do\o\do\p\do\q\do\r\do\s\do\t
     \do\u\do\v\do\w\do\x\do\y\do\z}
    {}%
  \let\do=\noexpand}

Unlike versions 1.4c to 1.6, this new definition no longer allows breakpoints at numbers, uppercase letters and lowercase letters by default. Breaks at these characters can be permitted by setting the penalty counters to a value between 0 and 10000, exclusive. For example:

\setcounter{biburlnumpenalty}{100}
\setcounter{biburlucpenalty}{100}
\setcounter{biburllcpenalty}{100}

The penalties can be reset locally using the command \defcounter from the etoolbox package (also loaded by biblatex). For example:

\defcounter{biburlnumpenalty}{3000}
\defcounter{biburlucpenalty}{6000}
\defcounter{biburllcpenalty}{9000}

To use this new setup with an older version of biblatex, just put the code defining \biburlsetup and its penalty counters in your preamble and replace \newcommand with \renewcommand.

Answer 2

Even for website references, my Zotero didn't export a url = ... line for .bib files, but just howpublished = {https://...}. This caused some URLs in the bibliography (I had to use multibib, not bibtex) to cause overful hboxes, and the URLs shoot out of the document without a line break. Apparently, behind the hood, there was no \url, but (I think?) a \href from the hyperref package, which has different behavior.

Out of the MANY options I tried, I ended up manually replacing the howpublished = {https://...} with a howpublished = {\url{https://...}} for the broken links. The URLs might look ugly then, this can be fixed with \urlstyle{rm} after \usepackage[hyphens]{url}.