Bash tool to get nth line from a file

Question

Is there a \"canonical\" way of doing that? I\'ve been using head -n | tail -1 which does the trick, but I\'ve been wondering if there\'s a Bash tool that speci

Answer 1

With awk it is pretty fast:

awk 'NR == num_line' file

When this is true, the default behaviour of awk is performed: {print $0}.

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Alternative versions

If your file happens to be huge, you'd better exit after reading the required line. This way you save CPU time ^{See time comparison at the end of the answer}.

awk 'NR == num_line {print; exit}' file

If you want to give the line number from a bash variable you can use:

awk 'NR == n' n=$num file
awk -v n=$num 'NR == n' file   # equivalent

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See how much time is saved by using exit, specially if the line happens to be in the first part of the file:

# Let's create a 10M lines file
for ((i=0; i<100000; i++)); do echo "bla bla"; done > 100Klines
for ((i=0; i<100; i++)); do cat 100Klines; done > 10Mlines

$ time awk 'NR == 1234567 {print}' 10Mlines
bla bla

real    0m1.303s
user    0m1.246s
sys 0m0.042s
$ time awk 'NR == 1234567 {print; exit}' 10Mlines
bla bla

real    0m0.198s
user    0m0.178s
sys 0m0.013s

So the difference is 0.198s vs 1.303s, around 6x times faster.