Command Blocks

Command blocks is the feature that distinguishes Hush from ordinary programming languages. They allow Hush scripts to seamlessly invoke and interconnect external programs.

Great effort has been put to make command syntax in Hush as similar as we’re used to in Bash, but some key aspects have been changed in order to favor robustness of scripts. You should never have to use something like the unofficial bash strict mode in Hush:

#!/bin/bash
set -euo pipefail
IFS=$'\n\t'

The unofficial bash strict mode

Let’s see why you won’t need any of this in Hush:

• set -e: interrupt execution immediately if a command has non-zero exit status. This is the default behavior for command blocks in Hush.
• set -u: exit with an error on any attempt to use an undeclared variable. Hush won’t even start to execute your script if you mention an undeclared variable.
• set -o pipefail: if a command in a pipeline fails, make the whole pipeline fail. This is the default behavior in Hush, and can even be controlled on a per-command basis in pipelines.
• IFS=$'\n\t': do word-splitting using only newlines and hard tabs. Hush does no word splitting whatsoever, so this will never be a source of confusion or bugs.

In the next sections, we’ll learn how to use command blocks in Hush.