What does this bash script involving "read" do?

Question

I found this in one of the bash scripts for capturing metrics running on CentOS.

read  -rd '' count <<< "$count"

I know read reads the content of file descriptor into buffer, but I cannot find the documentation for the command line switches -r, -d.

Additionally, What does triple left arrow <<< do?

Answer 1

All of these are Bash features which you will find amply documented in the Bash manual.

<<< is "here string" format; it's sort of like a here document:

cat <<____HERE
    Hello, World!
____HERE

... except the token after the separator is the actual string to pass in as standard input to the command.

The -r option to read disables some legacy behavior with backslashes from the original Bourne shell.

-d sets the record delimiter. An empty string says to stop reading when you get a NUL character.