awk: finding a missing field

You may come across a situation where not every field in a file has been populated as you'd expect. Now if this file is big you'll want a quick way to check to see if any records have missing fields. Here's a really simple example:

Input file:

44777123123,447786647774,447788772233
44777798982,,448879878873
4477334499882,44998878788,447887818733

awk -F',' '!$2 { print $0 }' test.txt

44777798982,,448879878873

As you can see we have a comma separated input file and we tell awk about it with the -F',' flag. Then we perform a test on every line of the file to determine if there is no 2nd field (!$2). If awk matches this pattern then it outputs the whole record ($0).