Output file lines from last to first in Bash

linux bash shell tail
Yarin picture Yarin · Nov 5, 2011 · Viewed 35.1k times · Source

I want to display the last 10 lines of my log file, starting with the last line- like a normal log reader. I thought this would be a variation of the tail command, but I can't find this anywhere.

Answer

Rick Smith picture Rick Smith · Nov 5, 2011

GNU (Linux) uses the following:

tail -n 10 <logfile> | tac

tail -n 10 <logfile> prints out the last 10 lines of the log file and tac (cat spelled backwards) reverses the order.

BSD (OS X) of tail uses the -r option:

tail -r -n 10 <logfile>

For both cases, you can try the following:

if hash tac 2>/dev/null; then tail -n 10 <logfile> | tac; else tail -n 10 -r <logfile>; fi

NOTE: The GNU manual states that the BSD -r option "can only reverse files that are at most as large as its buffer, which is typically 32 KiB" and that tac is more reliable. If buffer size is a problem and you cannot use tac, you may want to consider using @ata's answer which writes the functionality in bash.

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