jq, 20(削除) 20 (削除ここまで) 15 characters
now+.|strftime("%Y")|gmtime[0]
Sample run:
bash-5.0$ jq -r 'now+.|strftime("%Y")'|gmtime[0]' <<< 100000000000
5190
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Sample run:
bash-5.0$ jq -r 'now+.|strftime("%Y")'|gmtime[0]' <<< 100000000000
5190