Подкачка/зависание Linux при тяжелых компиляциях

Awksolución:

awk 'NR == FNR { a[$1] = $2 OFS; next }
     $2 in a { a[$2] = a[$2] (a[$2] ~ /\t$/? "" : ",") $1 }
     END { for (i in a) print i, a[i] }' OFS='\t' file1 file2

La salida:

bhy 30  c
abc 10  a,d,e
xyz 20  b,f

Para su última condición use la siguiente modificación:

awk 'NR == FNR { a[$1] = $2 OFS; next }
     $2 in a { a[$2] = a[$2] (a[$2] ~ /\t$/? "" : ",") $1 }
     END {
         for (i in a) print i, a[i] (a[i] ~ /\t$/? "Not_Available" : "")
     }' OFS='\t' file1 file2