Parameters/String Operations on shell (Bash) without using any third party tools

Parameter Substitution and Expansion:

Expression	Meaning
${var}	Value of var (same as $var)
${var-DEFAULT}	If var not set, evaluate expression as $DEFAULT *
${var:-DEFAULT}	If var not set or is empty, evaluate expression as $DEFAULT *
${var=DEFAULT}	If var not set, evaluate expression as $DEFAULT * (value is assigned to var)
${var:=DEFAULT}	If var not set, or is empty, evaluate expression as $DEFAULT * (value is assigned to var)
${var+OTHER}	If var set, evaluate expression as $OTHER, otherwise as null string
${var:+OTHER}	If var set, evaluate expression as $OTHER, otherwise as null string
${var?ERR_MSG}	If var not set, print $ERR_MSG and abort script with an exit status of 1.*
${var:?ERR_MSG}	If var not set, or is empty, print $ERR_MSG and abort script with an exit status of 1.*
${!varprefix*}	Matches all previously declared variables beginning with varprefix
${!varprefix@}	Matches all previously declared variables beginning with varprefix

* If var is set, evaluate the expression as $var with no side-effects.

String Operations:

Expression	Meaning
${#string}	Length of $string
${string:position}	Extract substring from $string at $position
${string:position:length}	Extract $length characters substring from $string at $position [zero-indexed, first character is at position 0]
${string#substring}	Strip shortest match of $substring from front of $string
${string##substring}	Strip longest match of $substring from front of $string
${string%substring}	Strip shortest match of $substring from back of $string
${string%%substring}	Strip longest match of $substring from back of $string
${string/substring/replacement}	Replace first match of $substring with $replacement
${string//substring/replacement}	Replace all matches of $substring with $replacement
${string/#substring/replacement}	If $substring matches front end of $string, substitute $replacement for $substring
${string/%substring/replacement}	If $substring matches back end of $string, substitute $replacement for $substring
expr match "$string" '$substring'	Length of matching $substring* at beginning of $string
expr "$string" : '$substring'	Length of matching $substring* at beginning of $string
expr index "$string" $substring	Numerical position in $string of first character in $substring* that matches [0 if no match, first character counts as position 1]
expr substr $string $position $length	Extract $length characters from $string starting at $position [0 if no match, first character counts as position 1]
expr match "$string" '\($substring\)'	Extract $substring*, searching from beginning of $string
expr "$string" : '\($substring\)'	Extract $substring* , searching from beginning of $string
expr match "$string" '.*\($substring\)'	Extract $substring*, searching from end of $string
expr "$string" : '.*\($substring\)'	Extract $substring*, searching from end of $string

* Where $substring is a Regular Expression.

Refer http://itsjustsosimple.blogspot.in/2013/02/all-about-variablesparameters-in-shell.htmlfor few examples.