AWK Matching Positive and Negative Numbers

Question

I have a data that looks like this:

-1033  
-  
222
100
-30
-
10

What I want to do is to capture all the numbers excluding "dash only" entry.

Why my awk below failed?

 awk '$4 != "-" {print $4}'

Answer 1

Your awk script says

If the fourth field is not a dash, print it out

However, you want to print it out if the line is not a dash

awk '$0 != "-"'

Default action is to print so no body is needed.

If you want to print group of numbers, you can use a GNU awk extension if you use gawk. It allows splitting records using regular expressions:

gawk 'BEGIN { RS="(^|\n)-($|\n)" } { print "Numbers:\n" $0 }'

Now, instead of lines, it takes a group of numbers separated by a line containing only -. Setting the field separator (FS) to a newline allows you to iterate over the numbers within such a group:

gawk 'BEGIN { FS="\n"; RS="(^|\n)-($|\n)" } 
      { print "Numbers:"; for(i=1;i<=NF;i++) print " *: " $i }'

However I agree with other answers. If you just want to filter out lines matching some text, grep is the better tool for that.

Answer 2

Assuming that your data file is actually multi-column, and that the values are in column 4, the following will work:

awk '$4 != "-" {print $4} {}'

It prints the value only where it isn't "-". Your version will probably print the value regardless (or twice) since the default action is to print. Adding the {} makes the default action "do nothing".

If the data is actually as shown (one column only), you should be using $1 rather than $4 - I wouldn't use $0 since that's the whole line and it appears you have spaces at the end of your first two lines which would cause $0 to be "-1033 " and "- ".

But, if it were a single column, I wouldn't use awk at all but rather:

grep -v '^-$'
grep -v '^ *- *$'

the second allowing for spaces on either side of the "-" character.

Answer 3

Why are you checking $4? It appears you should check $1 or $0 as litb said.

But awk is a heavyweight tool for this job. Try

grep -v '^-$'

To remove lines containing only a dash or

grep -v '^ *- *$'

To remove lines containing only a dash and possibly some space characters.