sed example

sed.sh

# search and replace with backup
# with -i it specifies a backup. So the file will be copied from myfile.txt to myfile.txt.bak before replacing any text.
# the * at the end is the filename. It can be myfile.* or *.txt or * or myfile.txt or whatever.

# mac version
sed -i .bak 's/hello/gbye/g' *
# linux version
sed -ibak 's/hello/gbye/g' *
# or just
sed 's/hello/gbye/g' *

# without backup
sed -i '' 's/hello/gbye/g' *

# specific file types
sed -i '' 's/hello/gbye/g' *.txt