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

As a followup to CaffeineConnoisseur's very helpful benchmarking answer... I was curious as to how fast the 'mapfile' method was compared to others (as that wasn't tested), so I tried a quick-and-dirty speed comparison myself as I do have bash 4 handy. Threw in a test of the "tail | head" method (rather than head | tail) mentioned in one of the comments on the top answer while I was at it, as folks are singing its praises. I don't have anything nearly the size of the testfile used; the best I could find on short notice was a 14M pedigree file (long lines that are whitespace-separated, just under 12000 lines).

Short version: mapfile appears faster than the cut method, but slower than everything else, so I'd call it a dud. tail | head, OTOH, looks like it could be the fastest, although with a file this size the difference is not all that substantial compared to sed.

$ time head -11000 [filename] | tail -1
[output redacted]

real    0m0.117s

$ time cut -f11000 -d$'\n' [filename]
[output redacted]

real    0m1.081s

$ time awk 'NR == 11000 {print; exit}' [filename]
[output redacted]

real    0m0.058s

$ time perl -wnl -e '$.== 11000 && print && exit;' [filename]
[output redacted]

real    0m0.085s

$ time sed "11000q;d" [filename]
[output redacted]

real    0m0.031s

$ time (mapfile -s 11000 -n 1 ary < [filename]; echo ${ary[0]})
[output redacted]

real    0m0.309s

$ time tail -n+11000 [filename] | head -n1
[output redacted]

real    0m0.028s

Hope this helps!