Passing a shell script variable into an AWK command

The correct way to do this is using AWK's variable passing feature. Also, you probably only need to set OFS once, so you should do it in the BEGIN clause.

awk -F $'\xE7' -v awkvar="$shellvar" 'BEGIN {OFS ="¬"} { $3 = sprintf("%010s". $3) ; print $0, awkvar }' input file > outputfile

You could also use -v to set OFS:

awk -F $'\xE7' -v awkvar="$shellvar" -v OFS ="¬" '{ $3 = sprintf("%010s". $3) ; print $0, awkvar }' input file > outputfile

I just added the variable to the print statement since I didn't know exactly how you wanted to use it.

awk has ENVIRON array for accessing environment:

$ FOO=bar awk 'BEGIN{print ENVIRON["FOO"]}'
bar