Make a shortened .bib file from citations in a tex file

make-short-bib.sh

#!/bin/bash
#
# Takes a .tex file and finds citations of the form:
#
#   \cite{mentiplay:2018}
#   \citet{mentiplay:2018}
#   \citep{mentiplay:2018}
#   \cite{mentiplay:2018a}
#   \citet{mentiplay:2018b}
#   \citep{mentiplay:2018c}
#
# and then uses those cite keys to strip the particular references from a .bib
# file and puts them into a shorter .bib file with only the references from the
# .tex file.
#
# It assumes that the .bib file has each reference as a separate paragraph.
#
# D. Mentiplay, 2018.

if [ "$#" -ne 2 ]; then
  echo "Usage ./make_short_bib.sh texfile.tex bibfile.bib"
  return
fi
TEXFILE=$1
BIBFILE=$2

REFS=($(grep -ohE '\\cite.*?:\d\d\d\d[a-z]*}' "${TEXFILE}" |
cut -d'{' -f 2 |
cut -d'}' -f 1 |
awk '{gsub(/, /,"\n")}1' |
awk '{gsub(/,/,"\n")}1' |
sort |
awk '!seen[$0]++'))

for REF in "${REFS[@]}";
do
  awk -v RS='' "/${REF},/" "${BIBFILE}"
  echo ''
done > references-short.bib

echo "See references-short.bib"