Shell Programming and Scripting

grep -n $tgt  file.txt | cut -f 1 -d ":"

varname=$( grep -n "$tgt" file.txt | cut -f 1 -d ":" )

for var in ` grep -n pattern file_name | cut -f 1 -d ":" `; do
echo "it has line number:$var"   #do your operations
done

$ sed $var`s`/$oldpattern/$newpattern file.txt

sed -i 's/pattern/replacement/' file.txt

sed "$var s/$oldpattern/$newpattern/" file.txt

sed '
s/pattern1/newpattern1/
s/pattern2/newpattern2/
' file.txt

sed '
/addrpattern1/ s/pattern1/newpattern1/
/addrpattern2/ s/pattern2/newpattern2/
' file.txt