Perl Learning II: Simple variables

String variable: ${}
1. Single quote: Do not replace the variable, do not escape, the string can cross the line.
2. Double quotes: variable substitution (greedy matching principle), support escape character (escape character can be seen separately)
3. Anti-Quote

Special notation for strings:
QQ (...)
Q (...)
() can be swapped for <>,{},[],//,;;, etc. paired characters.

Variable Initial value:
Undef $a
Defined $a
Generally used in conditional judgment
Integer initial value is 0
String initial value is empty string

Related functions:
Length ()----string lengths, number of digits
Chop ()
Chomp ()
The meaning of $/
The above function is rich in usage and can be removed at any end of the character.

Perl Learning II: Simple variables