Shell Programming and Scripting

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..,

awk 'FNR==1 {old=$1}
       old != $1 {printf("\n")}
       {print $0; old=$1} ' oldfile > newfile

awk '$1 != X && X = $1 { if(NR>1)print "" } 1' file

cat test.txt|cut -d' ' -f1|sort -u |while read i
do
cat test.txt|grep ^$i >> test1.txt
echo " " >> test1.txt
 done

awk '$1!=p{if(NR>1)print x; p=$1}1' infile