Usage of readarray and tac

Question

I have a file containing "lines" of text, for now only two lines. I need to create a reversed array of these lines - FIFO style.

Using "readarray" in this fashion works fine:

readarray -t FileArray < "$PWD$DEBUG_DIR$DEBUG_MENU"

When I attempt to "reverse" the file I get gibberish:

readarray -t FileArray < tac "$PWD$DEBUG_DIR$DEBUG_MENU"

I am still learning about substitution and it is obvious I am not using the tac command correctly. I did try different "syntax" without success.

Related: [Bash - reverse an array](//unix.stackexchange.com/q/412868) — Stéphane Chazelas, Sep 10 '18 at 14:36
Yes, there are other ways to reverse the file, my question was about how to get the tac results into the array. — , Sep 10 '18 at 15:01
note that one of the answers there shows how to use `readarray` with `tac`. — Stéphane Chazelas, Sep 10 '18 at 15:36

pLumo · Accepted Answer · 2018-09-10T14:21:10.483

2

Input redirection (as in cat < file) means the shell is opening the input file and writes its contents to the standard input of another process. It is not possible to just put a command after <.

But you can use Process Substitution to create a file descriptor from the output of the command using the following syntax:

<(some_command)

This is similar to using output from a command like a variable using $(some_command).

Try this:

readarray -t FileArray < <(tac "$PWD$DEBUG_DIR$DEBUG_MENU")

edited Sep 10 '18 at 14:21

answered Sep 10 '18 at 13:44

pLumo

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Thanks works as advertized. I guess ti need to atke a closer look at file desrtiptors. – Sep 10 '18 at 14:01
Not sure what is going on here , but this has been solved. – Sep 11 '18 at 22:18

Usage of readarray and tac

1 Answers1