UNIX for Dummies Questions & Answers

cat in_file | nawk '{RS=""; FS="\n"; ORS="\n\n"; OFS="\n"} /searchstring/ {print}' > out_file

#!/bin/bash

STRING="MARK"
MODE="start"

TMP=`mktemp`
exec 5>$TMP

while IFS="" read LINE
do
        case "$MODE" in
        start)
                if [[ "$LINE" =~ $STRING ]]
                then
                        MODE="mid"
                        echo "$LINE"
                fi
                ;;
        mid)    if [[ "$LINE" =~ $STRING ]]
                then
                        cat $TMP
                        echo $LINE
                        echo > $TMP
                        exec 5>$TMP
                else
                        echo "$LINE" >&5
                fi
                ;;
        esac
        :
done <<EOF
a b
MARK
asdf1
asdf2
MARK
asdf3
asdf4
MARK
qwerty5
EOF

rm -f $TMP