Question about a awk command

jeffwang66 · 11-13-2013, 10:38 AM

Hi,

I am studying an awk command:

awk '{ sub(/\/\/.*/, "", $NF); print }' input.txt

The input.txt is:

char*s1="//hello"; //comment
//delete
/* hello //*/

The output is :

char*s1="//hello";

/* hello

My question is why the contents ("//hello") is not deleted? And what does $NF mean?

Thanks

druuna · 11-13-2013, 11:10 AM

The NF variable is an awk internal and holds the number of fields for the current line that is processed.

This sub(/\/\/.*/, "", $NF) will do the substitution on the last field.

/* hello //*/ is 3 fields and the substitution is done on the last field only, hence the /* hello being outputted.

EDIT: Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR

grail · 11-13-2013, 11:24 PM

Quote:

My question is why the contents ("//hello") is not deleted?

As per druuna's explanation to NF, it would imply there is white space between the semicolon and the slashes in front of comment, which would mean '//comment' is the last field
on the line and so only it is removed.