Problems understanding Ruby code

Question

I have this code:

all_backups = dir.entries[2..-1].sort.reverse
max_backups = 20
unwanted_backups = all_backups[max_backups..-1] || []

I think it gets all entries in a defined folder. What is [2..-1]? What is all_backups[max_backups..-1] || []?

@Felix I'm sorry, but can you please clarify what you mean with your comment on @R_O_R's answer? By last 20, do you mean, the last 20 entries of all_backups or of unwanted_backups? And may I know what do you mean by oldest? Can you please tell where the oldest entries be located? (by way of array index) — Jason Adrian Bargas
– Jason Adrian Bargas, Commented Jun 4, 2015 at 7:45

Arup Rakshit · Accepted Answer · 2015-06-04 07:22:02Z

1

dir.entries[2..-1]

get elements from index 2(means 3rd element of your array) to last index(last element of your array). In Ruby -1 means last element of the Array instance.

all_backups[max_backups..-1] || []

all_backups[max_backups..-1] gives nil, then assign with an empty array [] to the variables other wise returned array from all_backups[max_backups..-1].

edited Jun 4, 2015 at 7:22

answered Jun 4, 2015 at 7:20

Arup Rakshit

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1 Comment

Felix Over a year ago

thanks. What I want to do: I make mysql dumps from a database and I want to save the last 20 backups. But with the code above 20 backups were saved, when the 21 is going to save all 20 backups will be deleted .. The oldest one should be deleted ...

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