I have many files of hourly values over the entire year. The awk script I used to add the hour to the date and data values had an error: I entered 16:00 (4pm) twice and now I need to change the second instance to 17:00. I have no prior experience with awk flags so this is the latest iteration of my script:

#!/usr/bin/gawk
# This script replaces the second instance of 16:00 with 17:00.

BEGIN { FS=","; OFS="," }
$2!="16.00" { print }
$2=="16:00" { print ; flag=1 }
$2=="16:00" { $2=="17:00"; flag=0; print }

It prints the input file without change.

This is a test data set, test.dat:

2012-10-01,14:00,90.7999
2012-10-01,15:00,90.8121
2012-10-01,16:00,90.8121
2012-10-01,16:00,90.8121
2012-10-01,18:00,90.8091
2012-10-01,19:00,90.8030

Each file is 8,761 lines long (a header line is on the top), and I have a dozen or so years that need correcting. I want to learn how to do this correction with awk.

I guess I would do it like this:

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Please remember to use [code][/code] tags around your code to preserve formatting and readability.

You were already fairly close, you just needed to use your flag variable to test when to make the change to $2

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Smallpond/Grail:

Thank you both for solutions. I've not before used a flag in awk and you both helped me understand how to use them.

Regards,

Rich

Based on your original code
Note the order: 1. test the flag 2. set the flag
So 1. can only be true in a following line.