Replace a word with another in bash

You can use sed for that:

$ sed s/sara/mary/g <<< 'hello sara , my name is sara too .'
hello mary , my name is mary too .

Or if you want to change a file in place:

$ cat FILE
hello sara , my name is sara too .
$ sed -i s/sara/mary/g FILE
$ cat FILE
hello mary , my name is mary too .

You can use sed:

# sed 's/sara/mary/g' FILENAME

will output the results. The s/// construct means search and replace using regular expressions. The 'g' at the end means "every instance" (not just the first).

You can also use perl and edit the file in place:

# perl -p -i -e 's/sara/mary/g;' FILENAME

Or awk

awk '{gsub("sara","mary")}1' <<< "hello sara, my name is sara too."

Pure bash way:

before='hello sara , my name is sara too .'
after="${before//sara/mary}"
echo "$after"

OR using sed:

after=$(sed 's/sara/mary/g' <<< "$before")
echo "$after"

OUTPUT:

hello mary , my name is mary too .