perl - If a line starts with a specific word, how to change a targeted word in that line if it does exist? -

looking search through files in directory, looking @ every line , if line starts word such "this", search line find , replace targeted word. did solution being 1 line command, looking have perl file or .txt file using bash if possible.

example:

this rabbit jumped high  rabbit jumped high 

(find , replace high low if line starts "this:

this rabbit jumped low  rabbit jumped high 

sed '/^this/{s/high/low/g}' file 

will you:

kent$  echo "this rabbit jumped high  rabbit jumped high"|sed '/^this/{s/high/low/g}' rabbit jumped low  rabbit jumped high 

if want replace word "high" instead of text high:

sed '/^this/{s/\<high\>/low/g}' file 

for example:

kent$  echo "this rabbit jumped high highfoo        rabbit jumped high"|sed '/^this/{s/\<high\>/low/g}'  rabbit jumped low highfoo  rabbit jumped high