As you can see in this answer. It seems like editing a text file in-place takes much more time than creating a new file, deleting the old file and moving a temporary file from another file-system and renaming it. Let alone creating a new file in the same file-system and just renaming it. I was wondering what is the reason behind that?
Because when you edit a file inplace you are opening the same file for both writing and reading. But when you use another file. you only read from one file and write to another file. When you open a file for reading it's content are moved from disk to memory. Then after, when you want to edit the file you change the content of the file in the disk so the content you have in memory should be updated to prevent data inconsistency. But when you use a new file. You don't have to update the contents of the first file in the memory. You just read the whole file once and write the other file once. And don't update anything. Removing a file also takes very small time because you just remove it from the file system and you don't write any bits to the location of the file in the disk. The same goes for renaming. Moving can also be done very fast depending on the file-system but most likely not as fast as removing and renaming.
There is also another more important reason.
When you remove the numbers from the beginning of the first line, all of the other characters have to be shifted back a little. Then when you remove the numbers from the second line again all of the characters after that point have to be shifted back because the characters have to be consecutive. If you wanted to just change some characters, editing in place would have been a lit faster. But since you are changing the length of the file on each removal all of the other characters have to get shifted and that takes so much time. It's not exactly like this and it's much more complicated depending on the implementation of your operation system and your file-system but this is the idea behind it. It's like array operation. When you remove a single element from an array you have to shift all of the other elements of the array. Because it is an array. In contrast if you were to remove an element from a linked list you didn't need to shift other elements but files are implemented similar to arrays so that is that.