Shell Programming and Scripting

An awk statement has the form:

Code:

condition {action}

Conditions in awk control the execution of actions and actions are executed when the condition is true.
If the condition is true (1 is true) and there are no actions between braces, awk prints the current record by default.

Code:

awk NF-1 infile

The NF variable gives the number of fields in a line.
If a line has 1 column (NF=1) the condition NF-1 (1-1=0) is false, so only lines with more then one field should be printed.

Code:

awk '$2' infile

This condition is true if a second column exists, all lines with one field are ignored.

If there is only one field then NF equals 1, 1-1=0 . So the default action (print $0) is not performed. If there are 2 or more fields the line does not get printed.. If NF>1 then the result is >=1 so the line does get printed.

The same goes for awk '$2' . If $2 exists, in other words there are two or more fields then the line gets printed.

The difference is the first solution prints empty lines. The second solution discards them and also does not print the line if $2 contains the value 0.

To skip empty lines and print $2 if it is 0, one could use one of these:

Code:

awk '$2""' infile

Code:

awk 'NF>1' infile

awk NF-1 means
show just 1st(or more) fields. if the line has 2 fields (2 columns) it will show just NF-1=2-1=1 field.

so, NF-1 will show only lines having 2 or more fields

hi

thanks a lot for ur reply