Bash Variables Substitutions
This table summarizes Bash parameter expansions, providing a quick reference for manipulating shell variables. It covers operations like default value assignment, substring extraction, pattern removal, case conversion, and string length calculation.
Parameter Expansion Description ${parameter:-defaultValue} Get default shell variables value ${parameter:=defaultValue} Set default shell variables value ${parameter:?"Error Message"} Display an error message if parameter is not set ${#var} Find the length of the string ${var%pattern} Remove from shortest rear (end) pattern ${var%%pattern} Remove from longest rear (end) pattern ${var:num1:num2} Substring ${var#pattern} Remove from shortest front pattern ${var##pattern} Remove from longest front pattern ${var/pattern/string} Find and replace (only replace first occurrence) ${var//pattern/string} Find and replace all occurrences ${!prefix*} Expands to the names of variables whose names begin with prefix. ${var,} Convert first character to lowercase. ${var,pattern} Convert first character to lowercase. ${var,,} Convert all characters to lowercase. ${var,,pattern} Convert all characters to lowercase. ${var^} Convert first character to uppercase. ${var^pattern} Convert first character to uppercase. ${var^^} Convert all character to uppercase. ${var^^pattern} Convert all character to uppercase.
