AWK: Preserving the format when printing "print $0"

Question

I am trying to use AWK for manipulating two files. Well I am actually interpolating between the two. Since I am not that much familiar how to process two files simultaneously with AWK I first do a paste

paste file_1 file_2 > mixed_file

each of those files contains lines of the following type

   2.02646E+12  ERR   7.39921E+09 EG =   67
   1.82357E+12  ERR   7.01570E+09 EG =   68
   8.65566E+11  ERR   4.35764E+09 EG =   69

The newly created file 'mixed_file' looks like this

 2.02646E+12  ERR   7.39921E+09 EG =   67        2.02646E+12  ERR   7.39921E+09 EG =   67
 1.82357E+12  ERR   7.01570E+09 EG =   68        1.82357E+12  ERR   7.01570E+09 EG =   68
 8.65566E+11  ERR   4.35764E+09 EG =   69        8.65566E+11  ERR   4.35764E+09 EG =   69

And here is my problem: when I try doing something like

awk  ' / EG = / {$1=0.5*($1+$7)}  {print $0} ' mixed_file

I get my formatting totally wrong

2026460000000 ERR 7.39921E+09 EG = 67 2.02646E+12 ERR 7.39921E+09 EG = 67
1823570000000 ERR 7.01570E+09 EG = 68 1.82357E+12 ERR 7.01570E+09 EG = 68
865566000000 ERR 4.35764E+09 EG = 69 8.65566E+11 ERR 4.35764E+09 EG = 69

I presume that the change in $1 is most probably due to mixing floats with characters. It is in principle possible to explicitly define the format and avoid this problem by using "printf", but I guess that more elegant solution exists.

AWK experts I would appreciate your help,

Thank you

Alex

Answer 1

Reassigning back to $0 is what you're after:

awk  '/ EG = / {$0 = sprintf(" %7.5E%s", 0.5*($1+$7), substr($0,13))} 1' mixed_file

Answer 2

When you assign to a field awk re-formats the line.

It does that using the value of OFS (by default a space).

Your input had multiply spaced columns. awk doesn't recreate that.

You can pipe to column -t to recreate that sort of output if you want.

You can also set OFS to a tab (\t) if that gets you the output you want.

I don't know of a way to get awk itself to preserve input formatting though (though I think that the RT variable in newer versions of gawk might allow that to be done manually).