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#!/usr/bin/env bash
set -euo pipefail

The first statement is a Mac, GNU/Linux, and BSD portable way of finding the location of the bash interpreter. The second statement combines

1. “set -e” which ensures that your script stops on first command failure. By default, when a command fails, BASH executes the next command. Looking at the logs, you might feel that the script executed successfully while some commands might have failed. Caveat: Be careful about applying it to existing scripts.
2. “set -u” which ensures that your script exits on the first unset variable encountered. Otherwise, bash replaces the unset variables with empty default values.
3. “set -o pipefail” which ensures that if any command in a set of piped commands failed, the overall exit status is the status of the failed command. Otherwise, the exit status is the status of the last command.

References:

1. Unofficial Bash strict mode
2. ExplainShell