Re: Input line splitting and OFS

[Peter Brooks]

Why not just evaluate into another variable, then you've still got the
original line to re-interpret?

On Fri, 15 Nov 2019 at 10:36, address@hidden
<address@hidden> wrote:
>
> 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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-- 
Peter Brooks

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