Script

Header ​

#!/bin/bash

Read from pipe / stdin ​

-t 0 is True if file descriptor is open and refers to a terminal. The cat - outputs the input file.

if [[ ! -t 0 ]]; then
  stdin=$(cat -)
fi

Using the built-in read:

##!/bin/bash
while IFS= read -r line; do
  printf '%s\n' "$line"
done

Eval ​

Evaluates a string as a shell command.

eval ${MYVAR}