Bash 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 start of $string
${string##substring}                       Strip longest match of $substring from start of $string
${string%substring}                        Strip shortest match of $substring from end of $string
${string%%substring}                       Strip longest match of $substring from end 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 start of $string, substitute $replacement for $substring
${string/%substring/replacement}           If $substring matches 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