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Split a data file
======================================================================
>cat t.dat
11 hello11
21 hello21
31 hello31
41 hello41

>cat t.ksh
#!/bin/ksh
# lines starting with 1 go to t1.txt
# lines starting with 2 go to t2.txt etc
while read i
do
awk 'substr($1,1,1) == 1 { print $1 > "t1.txt" }
     substr($1,1,1) == 2 { print $1 > "t2.txt" }
     substr($1,1,1) == 3 { print $1 > "t3.txt" }
     substr($1,1,1) == 4 { print $1 > "t4.txt" }'
done < t.dat