# Bash Parameter Subsitition

Variable Description
$ Get default shell variables value
$ Set default shell variables value
${parameter:?"Error Message"} Display an error message if parameter is not set
$ Find the length of the string
${var%pattern} Remove from shortest rear (end) pattern
${var%%pattern} Remove from longest rear (end) pattern
$ 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,} ${var,pattern} Convert first character to lowercase.
${var,,} ${var,,pattern} Convert all characters to lowercase.
${var^} ${var^pattern} Convert first character to uppercase.
${var^^} ${var^^pattern} Convert all character to uppercase.

# References