Question

I am finding the difference between two columns in a file like

cat "trace-0-dir2.txt" | awk '{print expr $2-$1}' | sort 

this gives me values like :

-1.28339e+09
-1.28339e+09
-1.28339e+09
-1.28339e+09

I want to avoid the rounding off and want the exact value.How can this be achieved?
FYI ,trace-0-dir2.txt contains:

1283453524.342134 65337.141749 10 2
1283453524.556784 65337.388047 11 2
1283453524.556794 65337.411165 12 2
1283453524.556806 65337.435947 13 2
1283453524.556811 65337.435989 14 2
1283453524.556816 65337.453931 15 2
1283453524.771522 65337.484866 16 2

Answer 1

printf function can help get you the formatting you need. You don’t need expr and you don’t need cat. awk can do any calculation and you can invoke awk directly on the file.

You can alter the 20.20 to any number based on the format you are looking for.

[jaypal:~/Temp] cat file0
1283453524.342134 65337.141749 10 2
1283453524.556784 65337.388047 11 2
1283453524.556794 65337.411165 12 2
1283453524.556806 65337.435947 13 2
1283453524.556811 65337.435989 14 2
1283453524.556816 65337.453931 15 2
1283453524.771522 65337.484866 16 2

[jaypal:~/Temp] awk '{ printf("%20.20f\n", $2-$1)}' file0
-1283388187.20038509368896484375
-1283388187.16873693466186523438
-1283388187.14562892913818359375
-1283388187.12085914611816406250
-1283388187.12082219123840332031
-1283388187.10288500785827636719
-1283388187.28665614128112792969

From the man page:

Field Width:

An optional digit string specifying a field width; if the output string has fewer characters than the field width it will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width (note that a leading zero is a flag, but an embedded zero is part of a field width);

Precision:

An optional period, `.’, followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, for e and f formats, or the maximum number of characters to be printed from a string; if the digit string is missing, the precision is treated as zero;