Replace one character with another in Bash

Use inline shell string replacement. Example:

foo="  "

# replace first blank only
bar=${foo/ /.}

# replace all blanks
bar=${foo// /.}

See http://tldp.org/LDP/abs/html/string-manipulation.html for more details.

You could use tr, like this:

tr " " .

Example:

# echo "hello world" | tr " " .
hello.world

---

From man tr:

DESCRIPTION
     Translate, squeeze, and/or delete characters from standard input, writ‐ ing to standard output.