Source once

source_once.bsh

The source_once.bsh script provides an easy to use guard that ensures a file will not be sourced (loaded) multiple times. This is analogous to C++’s header guards. This prevents circular source loops, saves time loading files, and produces less debugging output.

To activate the source once feature, the main script need only:

source ${VSI_COMMON_DIR}/linux/source_once.bsh

Every file that you want to be able to use this feature should have the following header

#!/usr/bin/env bash

if [[ ${-} != *i* ]]; then
  source_once &> /dev/null && return 0
fi

This header is written such that source_once is an optional component. If source_once.bsh hasn’t been sourced, this feature will do nothing, and continue.

In interactive mode, source_once is disabled and files are always source. This gives a more reliable experience to users in case files are updated, and prevents command_not_found_handle from triggering, which can be very costly.

Even though source_once.bsh is not dash compatible, a modified header can at least make the line that attempts to call source_once be dash compatible:

source_once > /dev/null 2>&1 && return 0

source_once

Output:

Returns 1 if this is the first time, else 0 for already called

Internal Use:

_VSI_ALREADY_SOURCED - State array used on bash 4 or newer
_VSI_ALREADY_SOURCED_* - State variables used for bash 3.2

Checks to see if the calling file has been used to call source_once. The intended use is to check if a file has been sourced already or not (by using BASH_SOURCE).