String length #

${#parameter} Expands into length of the string contained by parameter. If parameter is either ‘@’ or ‘*’ then results in number of positional parameters.

Substring expansion #

${parameter:offset} ${parameter:offset:length} Expands to portion of string defined by offset and length. End of string unless length is specified. If offset negative taken from end of string. (Space needed not to be confused with ${parameter:-word}, ${foo: -5}).

Substring removal #

${parameter#pattern} ${parameter##pattern} Remove leading portion of string contained in parameter defined by pattern. Pattern wildcard like used in pathname expansion. ‘#’ removes shortest match and ‘##’ removes longest match.

${parameter%pattern} ${parameter%%pattern} Sames as previous except they remove text from the end of the string contained in parameter.

Search and replace #

{parameter/pattern/string} {parameter//pattern/string} {parameter/#pattern/string} {parameter/%pattern/string} Expansions perform a search-and-replace on parameter. In normal form only first occurance is replaced. ‘//’ all occurrences replaced. If ‘/%’ ‘/#’ requires match occur at beginning of string ‘/%’ requires match occur at end of string In every occurance string may be omitted, causing text matching pattern to be deleted.