How to make awk system variables ”CONVERT“ and "IGNORECASE" work?

Question

I'm learning awk. I'm writing the code as:

awk 'BEGIN{IGNORECASE=1;print match("gridsphere",/D/)}'

I expect this code to print four, but it print zero.

And this:

awk 'BEGIN{data[10.15]="1200";CONVERT="%d";printf("<%s>",data[10.15])}'

I expect this code to print <> but it prints <1200>.

My question is why the variables IGNORECASE and CONVERT do not work.

My system is Ubuntu 20.04.

Answer 1

For your first item (IGNORECASE) check whether your Ubuntu system is using gawk (the GNU implementation of awk) or mawk (a different, more traditional implementation). Ubuntu supports installing either or both, and if both, which one is used for the name awk is controlled by the 'alternatives' package; check update-alternatives --display awk. IGNORECASE is a gawk extension and does not work in mawk (i.e. it's just a user variable with no special meaning).

awk 'BEGIN{data[10.15]="1200";CONVERT="%d";printf("<%s>",data[10.15])}'
I expect this code print <> but it print <1200>.

(corrected) Almost. CONVERT is not an awk 'system' variable (POSIX calls these 'special' variables and both gawk and mawk documentation call them 'built-in' or 'predefined'). CONVFMT is special/built-in, and affects conversions from noninteger number to string other than as a direct operand of print -- like your index/subscript; note specifying a string is NOT affected because that isn't doing conversion:

$ mawk 'BEGIN{data[10.15]="X";CONVFMT="%d";print "<"data[10.15]">";print "<"data["10.15"]">"}'
<>
<X>
$ gawk 'BEGIN{data[10.15]="X";CONVFMT="%d";print "<"data[10.15]">";print "<"data["10.15"]">"}'
<>
<X>