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copyleftdev/linux-tac.sh

Created May 25, 2026 20:44
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tac — reverse line order of any file or stream
Raw
linux-tac.sh
# tac — cat backwards: last line first
# (tac is cat spelled backwards)
tac logfile.log # reverse entire file
tac logfile.log | head -20 # last 20 lines, newest-first
tac logfile.log | grep -m1 'ERROR' # last occurrence of ERROR
# Process a JSONL file newest-first:
tac data.jsonl | head -5 | python3 -c "
import sys, json
for line in sys.stdin:
print(json.loads(line)['id'])
"
# vs tail -f: use tac for complete reversed files,
# use tail -f for live-streaming a growing file
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