That will match just the number 1, and not 11, or 111, etc.

It matches "1" and "1\n" only.

/^1$/:

1. At the start of the input,
2. match "1", then
3. optionally match "\n", then
4. match the end of the input string.

/^1\z/ will only match "1".

print "1 line of text" + 1;

will output the string "2". You start with a string and a number combined with the + operator. That operator takes two numbers as arguments, so perl attempts to convert the string to a number - this truncates from the first non-numeric character. We then evaluate 1+1 = 2. That two is then passed to the print subroutine, which takes a string input. Therefore, 2 is converted to "2" and output to STDOUT. Coming from a strongly-typed background, that still fills me with a profound warmth every time I do it.