It's string interpolation where you can provide an expression, not just a variable. > String interpolation is common in many programming languages which make h

It's string interpolation where you can provide an expression, not just a variable. > String interpolation is common in many programming languages which make heavy use of string representations of data, such as Apache Groovy, Kotlin, Perl, PHP, Python, Ruby, Scala, Swift, Tcl and most Unix shells. Two modes of literal expression are usually offered: one with interpolation enabled, the other without (termed raw string). Placeholders are usually represented by a bare or a named sigil (typically $ or %), e.g. $placeholder or %123. Expansion of the string usually occurs at run time. https://en.wikipedia.org/wiki/String_interpolation#%3A%7E%3Atext%3DString_interpolation_is_common_in%2CTcl_and_most_Unix_shells.?wprov=sfla1 https://en.wikipedia.org/wiki/String_interpolation#%3A%7E%3A...