Fastest way to print a single line in a file

Question

I have to fetch one specific line out of a big file (1500000 lines), multiple times in a loop over multiple files, I was asking my self what would be the best option

Answer 1

Drop the useless use of cat and do:

$ sed -n '1{p;q}' file

This will quit the sed script after the line has been printed.

---

Benchmarking script:

#!/bin/bash

TIMEFORMAT='%3R'
n=25
heading=('head -1 file' 'sed -n 1p file' "sed -n '1{p;q} file" 'read line < file && echo $line')

# files upto a hundred million lines (if your on slow machine decrease!!)
for (( j=1; j<=100,000,000;j=j*10 ))
do
    echo "Lines in file: $j"
    # create file containing j lines
    seq 1 $j > file
    # initial read of file
    cat file > /dev/null

    for comm in {0..3}
    do
        avg=0
        echo
        echo ${heading[$comm]}    
        for (( i=1; i<=$n; i++ ))
        do
            case $comm in
                0)
                    t=$( { time head -1 file > /dev/null; } 2>&1);;
                1)
                    t=$( { time sed -n 1p file > /dev/null; } 2>&1);;
                2)
                    t=$( { time sed '1{p;q}' file > /dev/null; } 2>&1);;
                3)
                    t=$( { time read line < file && echo $line > /dev/null; } 2>&1);;
            esac
            avg=$avg+$t
        done
        echo "scale=3;($avg)/$n" | bc
    done
done

Just save as benchmark.sh and run bash benchmark.sh.

Results:

head -1 file
.001

sed -n 1p file
.048

sed -n '1{p;q} file
.002

read line < file && echo $line
0

**Results from file with 1,000,000 lines.*

So the times for sed -n 1p will grow linearly with the length of the file but the timing for the other variations will be constant (and negligible) as they all quit after reading the first line:

Note: timings are different from original post due to being on a faster Linux box.