Input line splitting and OFS

[address@hidden]

Hi,

I have a question about the use of OFS as it relates to field splitting.

In a script I use I sometimes need to insert a field, based on the values in 
the current record. Subsequently I also need to test the value of that field. 
When I insert the field, I force gawk to re-evaluate the input line by using $0 
= $0.

Up until now this worked fine, but recently I was given a new use case where I 
sometimes need to set OFS to null, and later set it back to something else, 
again based on values in the input file. It's therefore impossible to predict 
in advance if and when this will occur.

The issue is that when I've set OFS = "", the re-evaluation uses that value to 
re-evaluate the input line, and so all the fields are concatenated into one.

The following code illustrates the issue :

# -------------------------------------
# fs_vs_ofs.awk
# -------------------------------------

BEGIN {
    FS = " "
#    OFS = ""
    split("a,b,c,d,e,f,x", tmp, ",")
    for (i in tmp) {
        valid_actions[tmp[i]]
    }
}
# -------------------------------------
{
    print NR " - before : " $0
    if ($2 == "b") {
        $2 = "x" FS $2
        $0 = $0
    }
    print NR " - after  : " $0
    for (i = 1; i <= NF; i++) {
        printf "   $%d : %s\n", i, $i
    }
    if ($2 in valid_actions) {
        print NR " - perform action " $2
    } else {
        print NR " - unknown action"
    }
}
# -------------------------------------

Sample data :

a b c
d e f

If line 7 is commented out, the actions are executed as expected, but if OFS is 
null they're not.

I would have expected that re-evaluating an _input_ line would use FS, not OFS, 
as it deals with input and not output.

Is this a bug, or is there an explanation for the use of OFS in this situation ?

Thanks for your help.

Kind regards,
Chris Newell

Chris Newell
Application Support Engineer
BAE Systems Applied Intelligence
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