Rename multiple files using one command

On Redhat Linux machine, suppose we have hundreds of .txt files, if want want to rename them to .sh file, there are a few ways to do:

1. use rename command

rename txt sh *.txt

2. write script

for f in *.txt; do mv $f ${f/.txt/.sh}; done

${f/.txt/.sh} is string replacement in bash, for details, please see string manipulation in bash