Question

I have a large string which is a collection of key (space)+ value, i.e key followed by one or more space and then value.
Now i need to change the value of a particular key using sed, awk, grep etc. in unix environment.

eg. of string: -Key1 Value1 -Key2 Value2 -Key3 Value3

I need a new string that is same as above only Value2 will be replaced by NewValue3

Answer 1

echo "-Key1 Value1 -Key2 Value2 -Key3 Value3" | \
    sed -r -e "s/(-Key2\s+)([^-\s]+)(\s+)/\1<newvale>\3/g"
-Key1 Value1 -Key2 <newvale> -Key3 Value3