How to add a string at the beginning of each line in a file

Question

I want to add a specific string at the beginning of each line in a file. So, if I have the below two lines in someFile.txt and want to add a date string 03/06/2012 with pipe-

Hello|there|john
Hello|there|joel

I would have-

03/06/2012|Hello|there|john
03/06/2012|Hello|there|joel

What would be the most efficient way to achieve this?

Answer 1

$ awk '{print "03/06/2012|" $0;}' input.txt > output.txt

Takes about 0.8 seconds for a file with 1.3M lines on some average 2010 hardware.

Answer 2

sed -i 's/^/03\/06\/2012|/' input.txt

Answer 3

Perl solution:

perl -ne 'print "03/06/2012|$_"' input.txt > output.txt

Just for fun, I benchmarked 10 runs in /tmp:

             Rate        awk perl_5.6.1        sed  perl_5.22  perl_5.20
awk        2.08/s         --       -10%       -10%       -26%       -32%
perl_5.6.1 2.32/s        11%         --        -0%       -17%       -24%
sed        2.33/s        12%         0%         --       -17%       -24%
perl_5.20  3.06/s        47%        32%        31%         9%         --

Tested using a 1.3M line input file created here:
perl -le 'while (1){exit if ++$n > 1300000; print $n}' > input.txt