uppercase first character in a variable with bash

One way with bash (version 4+):

foo=bar
echo "${foo^}"

prints:

Bar

$ foo="bar";
$ foo=`echo ${foo:0:1} | tr  '[a-z]' '[A-Z]'`${foo:1}
$ echo $foo
Bar

One way with sed:

echo "$(echo "$foo" | sed 's/.*/\u&/')"

Prints:

Bar

foo="$(tr '[:lower:]' '[:upper:]' <<< ${foo:0:1})${foo:1}"