How to magically add the file field to each entry in a bib file?

Question

In the context of biblatex its possible to bibstyle=reading, this will produce bibliography including abstract and annotation fields.

As well as file field linking to the file.pdf, the reference. If the bib entry has file set like:

@book{some-book,
 author     = {The Author},
 title      = {The Book Title},
 abstract   = {Bla bla bla},
 annotation = {Bla bla bla},
 file       = {some-book.pdf}
}

I have file.bib containing many entries, like:

@book{some-book,
 author     = {The Author},
 title      = {The Book Title},
 abstract   = {Bla bla bla},
 annotation = {Bla bla bla}
}

Following idea above I should go to each entry and add:

 file       = {some-book.pdf}

That will be a lot of work. Is it possible to automate it some way?

How to add file field to each entry without having to go to each entry and manually add it?

Answer 1

It is easily possible to add arbitrary field contents to entries with Biber's sourcemap features.

With

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authoryear, backend=biber]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex,overwrite=false]{
    \map{
      \step[fieldsource=entrykey, match={.*}, final]
      \step[fieldset=file, fieldvalue={$1.pdf}]
    }
  }
}

% just to print the 'file' field
\DeclareFieldFormat{file}{file: \path{#1}}
\renewbibmacro{finentry}{\printfield{file}\finentry}


\addbibresource{biblatex-examples.bib}

\begin{document}
\cite{sigfridsson,nussbaum,worman,geer}
\printbibliography
\end{document}

You would add to each entry the equivalent of

file = {<entrykey>.pdf},

to all entries that don't already have a file field.

---

You don't even need RegExes here, you could just say

\DeclareSourcemap{
  \maps[datatype=bibtex,overwrite=true]{
    \map{
      \step[fieldsource=entrykey, final]
      \step[fieldset=file, origfieldval, final]
      \step[fieldset=file, fieldvalue={.pdf}, append]
    }
  }
}

which would overwrite an existing file field. The overwrite=true is needed because an append step must formally be able to overwrite a field. You can guard against overwriting a pre-existing file field by adding

      \step[notfield=file, final]

as first step.

---

But it seems rather pointless to add a field file with the sole contents <entrykey>.pdf to all entries. The information you are adding is a very simple function of information that is already present in the entrykey field, after all.

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authoryear, backend=biber]{biblatex}


\DeclareFieldFormat{fakefile}{file: \path{#1.pdf}}
\renewbibmacro{finentry}{\printfield[fakefile]{entrykey}\finentry}


\addbibresource{biblatex-examples.bib}

\begin{document}
\cite{sigfridsson,nussbaum,worman,geer}
\printbibliography
\end{document}

Would produce the same result but without the need to map any field contents.