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up vote 3 down vote favorite

just wanted to check with you could this be done better:

awk -F"\t" '{
    for (i = 1; i <= NF; i++) {
        if ($i != "NULL") {
            printf("%s%s", $i, FS);
        }
    }

    printf("\n");
}' file1

The goal is to print only non-NULL fields. For example:

echo "TestRecord001 NULL    NULL    Age 29  NULL    NULL    Name    John" | awk -F"\t" '{
    for (i = 1; i <= NF; i++) {
        if ($i != "NULL") {
            printf("%s%s", $i, FS);
        }
    }

    printf("\n");
}'

will print out: TestRecord001 Age 29 Name John

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2 Answers 2

up vote 1 down vote accepted

The same behaviour can be achieved using sed as follows:

echo -e 'TestRecord001\tNULL\tNULL\tAge\t29\tNULL\tNULL\tName\tJohn' | sed '
s/$/\t/;
s/\(\tNULL\)\+\t/\t/g;
s/^NULL\t//';

Explanation:

sed s/SearchPattern/Replacement/g. Here s indicates that replacement operation is to be done. Strings matching SearchPattern will be replaced by Replacement. g indicates that the operation will have to be performed on every match and not just on the first occurrence in a line.

  1. s/$/\t/ adds a tab to the end of each line. [$ matches the end of a line]

  2. \(\tNULL\)\+\t matches a string of the form \tNULL\tNULL...NULL\t. This is replaced with \t.

  3. After this the only remaining NULL is the one at the beginning of a line (without \t to its left). This is matched by ^NULL\t and replaced with the empty string. [^ matches the beginning of a line]

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My previous answer was incorrect because NULL(\t\|$) matches with the ending portion of This-entry-is-not-NULL\t (which it shouldn't). –  S Prasanth Nov 27 '13 at 14:48
up vote 1 down vote

Your code is good.

I can't see anything to improve upon in your original code.

awk vs other tools (e.g sed)

I think awk is a good tool for this as you are dealing with input that has clearly defined fields and field separators. The code seems more readable in awk.

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