$ \textbf{cat .hg/hgrc}
[hooks]
pretxncommit.msglen = test `hg tip --template \{desc\} | wc -c` -ge 10
$ \textbf{echo a > a}
$ \textbf{hg add a}
$ \textbf{hg commit -A -m 'too short'}
transaction abort!
rollback completed
abort: pretxncommit.msglen hook exited with status 1
$ \textbf{hg commit -A -m 'long enough'}