Determine If Shell Input is Coming From the Terminal or From a Pipe

“Working on a little script the other day I had the need to
determine if the input to the script was coming from a pipe or from
the terminal. Seems like a simple enough thing to determine but
nothing jumped immediately to mind and a quick internet search
didn’t help much either. After a bit of pondering I came up with
two solutions: the stat command and using information from the proc
file system.

“The first solution uses the stat command to determine what type
of file is connected to standard input. First we find out what is
connected to standard input:”

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