AWK - Max Variables? - awk

Question

Why does the first statement work but not the second? I'm trying to add an additional two (one shown) variables to do another comparison, but the second instance errors out.
1st Instance
awk 'f1=substr($1,0,9), f2=substr($3,0,9){if(f1==f2)print $1,$2,$3,$4}' file
2nd Instance
awk 'f1=substr($1,0,9), f2=substr($3,0,9), f3=substr($1,5,3){if(f1==f2)print $1,$2,$3,$4}' file
awk: cmd. line:1: f1=substr($1,0,9), f2=substr($3,0,9), f3=substr($1,5,3){if(f1==f2)print $1,$2,$3,$4,16}
awk: cmd. line:1: ^ syntax error
File
TULSHDRJ02 ae0.0 KSCYBBRJ01 ae1.0
MTC3BBRJ02 ae4.0 KSCYBBRJ01 ae6.0
KSCYBBRJ01 ae2.0 KSCYBBRJ02 ae2.0
MTC1BBRJ02 ae4.0 KSCYBBRJ02 ae6.0
Output
KSCYBBRJ01 ae2.0 KSCYBBRJ02 ae2.0

Answer 1

$ awk 'substr($1,1,9)==substr($3,1,9){print $1,$2,$3,$4}' file
since you're printing everything you can drop the action part
$ awk 'substr($1,1,9)==substr($3,1,9)' file
or, for DRY
$ awk 'function s(v) {return substr(v,1,9)}
s($1)==s($3)' file

Answer 2

The general program structure of an awk program is as follows:
condition { action [; action [ ; ... ]] }
Multiple actions are separated by ; or newline.
Both the condition and the block of actions are optional. When you omit the condition
{ action [; action [ ; ... ]] }
... actions will be always executed. If you omit the actions:
condition
... the default action is print.
Multiple of those blocks can be put in a row:
cond1 { action1 } cond2 {action2} ...
Note: newline can be always used as a delimiter (for multiline programs)
I guess you wanted:
awk '{f1=substr($1,0,9);f2=substr($3,0,9)} f1==f2{print $1,$2,$3,$4}'
... or in multiline form:
awk '# Runs on every line
{
f1=substr($1,0,9)
f2=substr($3,0,9)
}
# Runs only if condition is met
f1==f2 {
print $1,$2,$3,$4
}'
But not quite!
It should be
awk '{f1=substr($1,1,9);f2=substr($3,1,9)} f1==f2{print $1,$2,$3,$4}'
instead of
awk '{f1=substr($1,0,9);f2=substr($3,0,9)} f1==f2{print $1,$2,$3,$4}'
Note that string, field and array indices in awk start at 1, not 0.
Please check also karakfa's answer, which shows how the command can be simplified.