Bash pattern to read from standard input or interactively in same program

June 25, 2021

I wanted a pattern to create programs program that can be used both interactively, or separately, as

$ program a b c

and as reading from standard input,

$ echo "some output" | program

The pattern is

!/bin/sh
if [ -t 0 ]; then
    echo running interactively
else
    while read -r line ; do
        echo $line
    done
fi