Output file lines from last to first in Bash

Question

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,

Answer 1

GNU (Linux) uses the following:

tail -n 10  | tac

tail -n 10 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 

For both cases, you can try the following:

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