Shell Programming and Scripting

 awk '{count[$1]++} END {for ( i in count ) print i, count[i] }'

 awk '{if(count[$1]++ >= max) max = count[$1]} END {for ( i in count ) if(max == count[i]) print i, count[i] }'

 a
 a
 a
 a
 a
 b
 b
 b
 c
 c

 a 5
 b 3

 a 50%
 b 30%

awk -v PCT=".3" '
        {if(++count[$1] > count[max]) max = $1
         tot++
        }
END     {# print max, count[max]                      # solution for the former problem
         for (c in count) if (count[c]/tot >= PCT) print c, count[c]
        }
' file
a 5
b 3