Shell Programming and Scripting

$ cat test.txt
AAA 1
AAA 2
BBB 5
BBB 7
BBB 9
CCC 3
CCC 4
DDD 6
EEE 5

AAA 2
BBB 9
CCC 4
DDD 6
EEE 5

#!/bin/ksh

INPUT=$1

sort $INPUT > $$ && mv $$ $INPUT

cut -d' ' -f1 $INPUT | sort | uniq -d > ROWS_WITH_MULTIPLE_VALUES
cut -d' ' -f1 $INPUT | sort | uniq -u > ROWS_WITH_SINGLE_VALUES

if [[ `cat ROWS_WITH_MULTIPLE_VALUES | wc -l` -gt 0 ]] ;
then

while read VALUE_1
do

    grep $VALUE_1 $INPUT | tail -1

done < ROWS_WITH_MULTIPLE_VALUES

fi;

if [[ `cat ROWS_WITH_SINGLE_VALUES | wc -l` -gt 0 ]] ;
then

while read VALUE_1
do

    grep $VALUE_1 $INPUT

done < ROWS_WITH_SINGLE_VALUES

fi;

rm ROWS_WITH_MULTIPLE_VALUES ROWS_WITH_SINGLE_VALUES

#!/bin/ksh
sort -rk2 $INPUT > temp
awk '!x[$1]++' temp > temp1
sort temp1 > $OUTPUT

sort -k1,1 -k2,2rn infile

sort -k1,1 -k2,2rn infile | awk '!x[$1]++'

awk '{a[$1]=(a[$1]>$2)?a[$1]:$2}END{for (i in a) print i,a[i]|"sort"}' test.txt