Tuesday, October 12, 2010

Using back references in SED

Today I have several CSV files, everyone with a header at the first line and a date at the first fields with the format mm/dd/yyyy. It was necessary to change that field into the format yyyy-mm-dd.

Here there is a Perl solution and also a SED one:

use strict;
use warnings;
while (<>) {
        if (/^[^0-9]/) {
                print "$_\n";
        my @Fields = split /,/, $_, 2;
        my ($Month, $Day, $Year) = split /\//, $Fields[0];
        print "$Year-$Month-$Day, $Fields[1]\n";

sed -i.bak 's/^\([0-9]\+\)\/\([0-9]\+\)\/\([0-9]\+\)/\3-\1-\2/' *.csv

Yesterday on my way home I realized that the Perl script was horrible, a one-liner should be OK, like the one below:

perl -i.bak -pe 's!(\d+)/(\d+)/(\d+)!\3-\1-\2!' *.csv

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