Read <<programming ruby>> 7.6 Verses flip-flop understanding

This is the source code in the book.

File.foreach ('1.txt') do |x|  if (($. = = 1) | | x =~/eig/). (($. = = 3) | | x =~/nin/)     Then Print x  endend

Where 1.txt content is as follows

Firstsecondthirdfourthfifthsixthseventheigthninthtenth

Read the first,$ of the first line. should be 1 ($. is a global variable that represents the line number) but RubyMine is not found in 1, this I did not find the reason for the moment. So I was prompted by others. I changed it.

f = file.new (' 1.txt ') F.each do |line|  if ((F.lineno = = 1) | | Line.chomp =~/eig/): ((f.lineno== 3) | | line.chomp =~/nin/) then    print F.lineno    print line  endend

　　

This f.lineno indicates that each read line number runs the test result as follows

Only 2 points were mentioned in the book.

1 Exp1. Expr2 such a rang, before EXP1 becomes true, its value is false, before EXP2 becomes true, rang is solved as true
2 This fragment of code. is to print between 1 and 3 lines and between/eig/and/nin/

A little obscure, and then a crowd of people prompted to read this article: http://nithinbekal.com/posts/ruby-flip-flop/

The flip flop operator is a range ( .. ) operator used between, conditions in a conditional statement. It looks like this:

(1..20). Each do |x|  Puts x if (x = = 5): (x = = Ten) end

　The condition evaluates to false every time it was evaluated until the first part evaluates to True. Then it evaluates-true until the second part evaluates to True. In the above example, the flip-flop was turned on while x == 5 and stays on until x == 10 , so the numbers from 5 to Printed.

(x = = 5).. (x = = 10) This thing is called the flip flop.

1 Blue English means when the first part is (x==5) true. The whole if judgment is true, but when is false. Until the second part is true (x==10), that  is the EXP1 mentioned earlier. Expr2 such a rang, before EXP1 becomes true, its value is false, before EXP2 becomes true, rang is solved as true 2  red words in English means x==5, this expression begins to execute. When to stop and know x==10, so print between 5 and 10

　　

So understand

((F.lineno = = 1) | | line.chomp =~/eig/) ... ((f.lineno== 3) | | Line.chomp =~/nin/)

You can think of this, when the F.lineno value is 1, the expression ((F.lineno = = 1) | | Line.chomp =~/eig/) is true, the whole if is true,

Then print 1first, when does the print end? , when the value of Flineno=3 or Line.chomp (Chomp minus the end of the line/r/n) matches the/nin/, the two of them will not print when they meet one of them.

Can be understood like the code below

f = file.new (' 1.txt ') F.each do |line|  if ((1..3) Include?f.lineno) or (line =~/eig/or line =~/nin/) then    print F.lineno    print line  endend

　　

Read <<programming ruby>> 7.6 Verses flip-flop understanding