While working on a my dissertation, I noticed that LaTeX was giving me a warning message:
LaTeX Warning: There were multiply-defined labels.
Since LaTeX didn’t feel the need to tell me which labels were multiply-defined, I had to find them myself. Finding these by hand is hard to impossible. Luckily, this perl script solves the problem:
perl -nE 'say $1 if /(\\label[^}]*})/' *.tex | sort | uniq -c | sort -n
Taken from here.