${parameter:-defaultValue}
${parameter:=defaultValue}
${parameter:?”ErrorMsg”}
${#var} - length of string
${var%pattern}
${var#Pattern} - Remove from $var the shortest part of $Pattern that matches the front end
${var##Pattern} - Remove from $var the longest part of $Pattern that matches the front end
${var%Pattern} - Remove from $var the shortest part of $Pattern that matches the back end
${var%%Pattern} - Remove from $var the longest part of $Pattern that matches the back end
${var:pos} - Variable var expanded, starting from offset pos.
${var:pos:len} - Expansion to a max of len characters of variable var, from offset pos
${var/Pattern/Replacement} - First match of Pattern, within var replaced with Replacement.
${var//Pattern/Replacement} - Global replacement. All matches of Pattern, within var replaced.
${var/#Pattern/Replacement} - If prefix of var matches Pattern, then substitute Replacement for Pattern.
${var/%Pattern/Replacement} - If suffix of var matches Pattern, then substitute Replacement for Pattern.
${!varprefix*}, ${!varprefix@} - Matches names of all previously declared variables beginning with varprefix.
numeric validation = [[ $var == ${var//[^0-9]/} ]] || echo “Not numeric”