Shell Programming and Scripting

awk '/^MALE/{print "AM" $0}' file

awk '/^MALE/{$0="AM" $0}1' file

#!/bin/sh
file="file1"
cp $file $file.bak
tf=$$.tmp
awk ' 
# rule and print 
/^MALE / { print "M",$0  ; next  }
/^FEMALE / { print "F",$0 ; next}
# default
{ print "?",$0 }
' $file > $tf
# overwrite original file
cat $tf > $file
rm -f $tf

echo 'MALE JOHN' | sed 's/^MALE /M MALE /; s/^FEMALE /F FEMALE /;'

M MALE JOHN

sed 's/^\([A-Z]\)/\1 \1/'

perl -ne '{s/^([A-Z])/(($1 eq "M")?"M ":($1 eq "F")?"F ":"O ").$1/e;print;}'