diff --git a/completion/available/apm.completion.bash b/completion/available/apm.completion.bash
index c3dcfe45f8..9737938f24 100644
--- a/completion/available/apm.completion.bash
+++ b/completion/available/apm.completion.bash
@@ -1,4 +1,4 @@
 # shellcheck shell=bash
 about-completion "apm completion"
-# shellcheck disable=SC1090
-source "${BASH_IT}"/vendor/github.com/vigo/apm-bash-completion/apm
+# shellcheck source-path=SCRIPTDIR/../../vendor/github.com/vigo/apm-bash-completion
+source "${BASH_IT?}/vendor/github.com/vigo/apm-bash-completion/apm"
diff --git a/completion/available/awless.completion.bash b/completion/available/awless.completion.bash
index 98a5d38881..ba7e422684 100644
--- a/completion/available/awless.completion.bash
+++ b/completion/available/awless.completion.bash
@@ -1,5 +1,16 @@
 # shellcheck shell=bash
-if _command_exists awless; then
-	# shellcheck disable=SC1090
-	source <(awless completion bash)
+
+# Make sure awless is installed
+if ! _binary_exists awless; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists awless; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# shellcheck disable=SC1090
+source <(awless completion bash)
diff --git a/completion/available/awscli.completion.bash b/completion/available/awscli.completion.bash
index a30418373a..4e46f40c2c 100644
--- a/completion/available/awscli.completion.bash
+++ b/completion/available/awscli.completion.bash
@@ -1,6 +1,14 @@
 # shellcheck shell=bash
 
-if _command_exists aws_completer
-then
-	complete -C "$(command -v aws_completer)" aws
+# Make sure aws is installed
+if ! _binary_exists aws_completer || ! _binary_exists aws; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists aws; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+complete -C aws_completer aws
diff --git a/completion/available/cargo.completion.bash b/completion/available/cargo.completion.bash
index d276ee7298..7a3d252008 100644
--- a/completion/available/cargo.completion.bash
+++ b/completion/available/cargo.completion.bash
@@ -1,6 +1,16 @@
 # shellcheck shell=bash
-# cargo (Rust package manager) completion
+about-completion "cargo (Rust package manager) completion"
 
-if _binary_exists rustup && _binary_exists cargo; then
-	eval "$(rustup completions bash cargo)"
+# Make sure cargo is installed
+if ! _binary_exists rustup || ! _binary_exists cargo; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists cargo; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(rustup completions bash cargo)"
diff --git a/completion/available/conda.completion.bash b/completion/available/conda.completion.bash
index f5a61e5907..84399caec3 100644
--- a/completion/available/conda.completion.bash
+++ b/completion/available/conda.completion.bash
@@ -1,5 +1,4 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "conda completion"
 
 if _command_exists conda; then
diff --git a/completion/available/consul.completion.bash b/completion/available/consul.completion.bash
index 511cf37209..84f46f4365 100644
--- a/completion/available/consul.completion.bash
+++ b/completion/available/consul.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "Hashicorp consul completion"
 
-if _command_exists consul; then
-	complete -C "$(command -v consul)" consul
+# Make sure consul is installed
+if ! _binary_exists consul; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists consul; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+complete -C consul consul
diff --git a/completion/available/crystal.completion.bash b/completion/available/crystal.completion.bash
index 7644ffd4d4..950459aa71 100644
--- a/completion/available/crystal.completion.bash
+++ b/completion/available/crystal.completion.bash
@@ -1 +1,4 @@
-_log_warning 'Bash completion for "crystal" is now covered by "system". This completion can be disabled.'
+# shellcheck shell=bash
+
+_log_warning 'Bash completion for "crystal" is now covered by "system".'
+_disable-completion "crystal"
diff --git a/completion/available/defaults.completion.bash b/completion/available/defaults.completion.bash
index 39d7ea95b0..9fb00da619 100644
--- a/completion/available/defaults.completion.bash
+++ b/completion/available/defaults.completion.bash
@@ -1,5 +1,6 @@
 # shellcheck shell=bash
 
-if test -s "${BASH_IT?}/vendor/github.com/gaelicWizard/bash-progcomp/defaults.completion.bash"; then
-	source "$_"
+if [[ -s "${BASH_IT?}/vendor/github.com/gaelicWizard/bash-progcomp/defaults.completion.bash" ]]; then
+	# shellcheck source-path=SCRIPTDIR/../../vendor/github.com/gaelicWizard/bash-progcomp
+	source "${BASH_IT?}/vendor/github.com/gaelicWizard/bash-progcomp/defaults.completion.bash"
 fi
diff --git a/completion/available/docker.completion.bash b/completion/available/docker.completion.bash
index 3f83a87461..ecbf29cf22 100644
--- a/completion/available/docker.completion.bash
+++ b/completion/available/docker.completion.bash
@@ -1,24 +1,37 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "docker completion"
 
 # Make sure docker is installed
-_command_exists docker || return
+if ! _binary_exists docker; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+fi
 
 # Don't handle completion if it's already managed
-_completion_exists docker && return
+if _completion_exists docker; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
 
 _docker_bash_completion_paths=(
-	# MacOS
+	# MacOS App
 	'/Applications/Docker.app/Contents/Resources/etc/docker.bash-completion'
-	# Linux
+	# Command Line
 	'/usr/share/bash-completion/completions/docker'
 )
 
-for fn in "${_docker_bash_completion_paths[@]}"; do
-	if [ -r "$fn" ]; then
+# Load the first completion file found
+_docker_bash_completion_found=false
+for _comp_path in "${_docker_bash_completion_paths[@]}"; do
+	if [[ -r "$_comp_path" ]]; then
+		_docker_bash_completion_found=true
 		# shellcheck disable=SC1090
-		source "$fn"
+		source "$_comp_path"
 		break
 	fi
 done
+
+# Cleanup
+if [[ "${_docker_bash_completion_found}" == false ]]; then
+	_log_warning "no completion files found - please try enabling the 'system' completion instead."
+fi
+unset "${!_docker_bash_completion@}"
diff --git a/completion/available/drush.completion.bash b/completion/available/drush.completion.bash
index 6628c65513..ccee2c3edf 100644
--- a/completion/available/drush.completion.bash
+++ b/completion/available/drush.completion.bash
@@ -1,2 +1,3 @@
+# shellcheck shell=bash
 _log_warning 'Bash completion for "drush" is now deprecated, as it used code with incompatible license.
 Please disable this completion and use the instructions from "drush" developers instead.'
diff --git a/completion/available/flutter.completion.bash b/completion/available/flutter.completion.bash
index 62befc824d..6627287611 100644
--- a/completion/available/flutter.completion.bash
+++ b/completion/available/flutter.completion.bash
@@ -1,5 +1,15 @@
-#!/usr/bin/bash
+# shellcheck shell=bash
 
-if _command_exists flutter; then
-  eval "$(flutter bash-completion)"
+# Make sure flutter is installed
+if ! _binary_exists flutter; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists flutter; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(flutter bash-completion)"
diff --git a/completion/available/gcloud.completion.bash b/completion/available/gcloud.completion.bash
index 63073e8ed3..514d8b4c3d 100644
--- a/completion/available/gcloud.completion.bash
+++ b/completion/available/gcloud.completion.bash
@@ -1,5 +1,4 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "Google Cloud SDK completion"
 
 if _command_exists gcloud; then
diff --git a/completion/available/github-cli.completion.bash b/completion/available/github-cli.completion.bash
index 4a6113945c..d10ba34e7d 100644
--- a/completion/available/github-cli.completion.bash
+++ b/completion/available/github-cli.completion.bash
@@ -1,9 +1,15 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "GitHub CLI completion"
 
-if _binary_exists gh; then
-	# If gh already completed, stop
-	_completion_exists gh && return
-	eval "$(gh completion --shell=bash)"
+if ! _binary_exists gh; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists gh; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(gh completion --shell=bash)"
diff --git a/completion/available/helm.completion.bash b/completion/available/helm.completion.bash
index 0dae7af46b..9809cfb7ff 100644
--- a/completion/available/helm.completion.bash
+++ b/completion/available/helm.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "helm (Kubernetes Package Manager) completion"
 
-if _command_exists helm; then
-	eval "$(helm completion bash)"
+# Make sure helm is installed
+if ! _binary_exists helm; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists helm; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(helm completion bash)"
diff --git a/completion/available/homesick.completion.bash b/completion/available/homesick.completion.bash
index ed6f6e79ed..41ab67f146 100644
--- a/completion/available/homesick.completion.bash
+++ b/completion/available/homesick.completion.bash
@@ -1,2 +1,3 @@
+# shellcheck shell=bash
 _log_warning 'Bash completion for "homesick" is now deprecated, as it used unlicensed code.
 Please disable this completion and use the instructions from "homesick" bash completion developers instead.'
diff --git a/completion/available/jungle.completion.bash b/completion/available/jungle.completion.bash
index e190d1438a..7ea8443b86 100644
--- a/completion/available/jungle.completion.bash
+++ b/completion/available/jungle.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "jungle(AWS cli tool) completion"
 
-if _command_exists jungle; then
-	eval "$(_JUNGLE_COMPLETE=source jungle)"
+# Make sure jungle is installed
+if ! _binary_exists jungle; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists jungle; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(_JUNGLE_COMPLETE=source jungle)"
diff --git a/completion/available/kind.completion.bash b/completion/available/kind.completion.bash
index be12a2d29c..abe8f0a4b8 100644
--- a/completion/available/kind.completion.bash
+++ b/completion/available/kind.completion.bash
@@ -1,5 +1,15 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 
-if _command_exists kind; then
-  eval "$(kind completion bash)"
+# Make sure kind is installed
+if ! _binary_exists kind; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists kind; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(kind completion bash)"
diff --git a/completion/available/kontena.completion.bash b/completion/available/kontena.completion.bash
index 916ee15f92..869bea9f58 100644
--- a/completion/available/kontena.completion.bash
+++ b/completion/available/kontena.completion.bash
@@ -1,5 +1,16 @@
 # shellcheck shell=bash
-if _command_exists kontena; then
-	# shellcheck disable=SC1090
-	source "$(kontena whoami --bash-completion-path)"
+
+# Make sure kontena is installed
+if ! _binary_exists kontena; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists kontena; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# shellcheck disable=SC1090
+source "$(kontena whoami --bash-completion-path)"
diff --git a/completion/available/kubectl.completion.bash b/completion/available/kubectl.completion.bash
index a9c498b601..1e09b10bc0 100644
--- a/completion/available/kubectl.completion.bash
+++ b/completion/available/kubectl.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "kubectl (Kubernetes CLI) completion"
 
-if _binary_exists kubectl; then
-	eval "$(kubectl completion bash)"
+# Make sure kubectl is installed
+if ! _binary_exists kubectl; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists kubectl; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(kubectl completion bash)"
diff --git a/completion/available/laravel.completion.bash b/completion/available/laravel.completion.bash
index 8f03256896..74ed8d620e 100644
--- a/completion/available/laravel.completion.bash
+++ b/completion/available/laravel.completion.bash
@@ -1,6 +1,15 @@
 # shellcheck shell=bash
 
-_command_exists laravel || return
+# Make sure laravel is installed
+if ! _binary_exists laravel; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+fi
+
+# Don't handle completion if it's already managed
+if _completion_exists laravel; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
 
 function __laravel_completion() {
 	local OPTS=('-h' '--help' '-q' '--quiet' '--ansi' '--no-ansi' '-n' '--no-interaction' '-v' '-vv' '-vvv' '--verbose' 'help' 'list' 'new')
diff --git a/completion/available/makefile.completion.bash b/completion/available/makefile.completion.bash
index e72ba6fd3b..b518bb5793 100644
--- a/completion/available/makefile.completion.bash
+++ b/completion/available/makefile.completion.bash
@@ -1,33 +1,35 @@
+# shellcheck shell=bash
+
 # Bash completion for Makefile
 # Loosely adapted from http://stackoverflow.com/a/38415982/1472048
 
-_makecomplete() {
-  COMPREPLY=()
+function _makecomplete() {
+	local cur="${COMP_WORDS[COMP_CWORD]}"
+	local files=() targets=() line f
+	COMPREPLY=()
 
-  # https://www.gnu.org/software/make/manual/html_node/Makefile-Names.html
-  local files=()
-  for f in 'GNUmakefile' 'makefile' 'Makefile' ; do
-    [ -f "$f" ] && files+=("$f")
-  done
+	# https://www.gnu.org/software/make/manual/html_node/Makefile-Names.html
+	for f in 'GNUmakefile' 'makefile' 'Makefile'; do
+		[[ -f "$f" ]] && files+=("$f")
+	done
 
-  [ "${#files[@]}" -eq 0 ] && return 0
+	[[ "${#files[@]}" -eq 0 ]] && return 0
 
-  # collect all targets
-  local targets=()
-  for f in "${files[@]}" ; do
-    while IFS='' read -r line ; do
-      targets+=("$line")
-    done < <(grep -oE '^[a-zA-Z0-9_-]+:([^=]|$)' "$f" | cut -d':' -f1)
-  done
+	# collect all targets
+	for f in "${files[@]}"; do
+		while IFS='' read -r line; do
+			targets+=("$line")
+		done < <(grep -oE '^[a-zA-Z0-9_-]+:([^=]|$)' "$f" | cut -d':' -f1)
+	done
 
-  [ "${#targets[@]}" -eq 0 ] && return 0
+	[[ "${#targets[@]}" -eq 0 ]] && return 0
 
-  # use the targets for completion
-  while IFS='' read -r line ; do
-    COMPREPLY+=("$line")
-  done < <(compgen -W "$(tr ' ' '\n' <<<"${targets[@]}" | sort -u)" -- "${COMP_WORDS[COMP_CWORD]}")
+	# use the targets for completion
+	while IFS='' read -r line; do
+		COMPREPLY+=("$line")
+	done < <(compgen -W "$(tr ' ' '\n' <<< "${targets[@]}" | sort -u)" -- "${cur}")
 
-  return 0
+	return 0
 }
 
 complete -o nospace -F _makecomplete make
diff --git a/completion/available/minikube.completion.bash b/completion/available/minikube.completion.bash
index 44076362ce..a90ef905a6 100644
--- a/completion/available/minikube.completion.bash
+++ b/completion/available/minikube.completion.bash
@@ -1,6 +1,16 @@
 # shellcheck shell=bash
-# minikube (Local Kubernetes) completion
+about-completion "minikube (Local Kubernetes) completion"
 
-if _command_exists minikube; then
-	eval "$(minikube completion bash)"
+# Make sure minikube is installed
+if ! _binary_exists minikube; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists minikube; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(minikube completion bash)"
diff --git a/completion/available/minishift.completion.bash b/completion/available/minishift.completion.bash
index 5679eae80f..f8525b331d 100644
--- a/completion/available/minishift.completion.bash
+++ b/completion/available/minishift.completion.bash
@@ -1 +1,16 @@
-_command_exists minishift && source <(minishift completion bash)
+# shellcheck shell=bash
+
+# Make sure minishift is installed
+if ! _binary_exists minishift; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
+fi
+
+# Don't handle completion if it's already managed
+if _completion_exists minishift; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# shellcheck disable=SC1090
+source <(minishift completion bash)
diff --git a/completion/available/ng.completion.bash b/completion/available/ng.completion.bash
index f219b30396..bc1ae8d140 100644
--- a/completion/available/ng.completion.bash
+++ b/completion/available/ng.completion.bash
@@ -1,8 +1,20 @@
-if _command_exists ng; then
-  # No longer supported, please see https://github.com/angular/angular-cli/issues/11043
-  # Fix courtesy of https://stackoverflow.com/questions/50194674/ng-completion-no-longer-exists
-  # . <(ng completion --bash)
+# shellcheck shell=bash
 
-  NG_COMMANDS="add build config doc e2e generate help lint new run serve test update version xi18n"
-  complete -W "$NG_COMMANDS" ng
+# Make sure ng is installed
+if ! _binary_exists ng; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists ng; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# No longer supported, please see https://github.com/angular/angular-cli/issues/11043
+# Fix courtesy of https://stackoverflow.com/questions/50194674/ng-completion-no-longer-exists
+# source <(ng completion --bash)
+
+_ng_bash_completion_candidates=("add" "build" "config" "doc" "e2e" "generate" "help" "lint" "new" "run" "serve" "test" "update" "version" "xi18n")
+complete -W "${_ng_bash_completion_candidates[*]}" ng
+unset "${!_ng_bash_completion@}"
diff --git a/completion/available/npm.completion.bash b/completion/available/npm.completion.bash
index cf24585ef7..7312ac54a5 100644
--- a/completion/available/npm.completion.bash
+++ b/completion/available/npm.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "npm (Node Package Manager) completion"
 
-if _command_exists npm; then
-	eval "$(npm completion)"
+# Make sure npm is installed
+if ! _binary_exists npm; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists npm; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(npm completion)"
diff --git a/completion/available/nvm.completion.bash b/completion/available/nvm.completion.bash
index a82b82b61a..9126f4d68b 100644
--- a/completion/available/nvm.completion.bash
+++ b/completion/available/nvm.completion.bash
@@ -1,8 +1,7 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+about-completion "nvm (Node Version Manager) completion"
 
-# nvm (Node Version Manager) completion
-
-if [ "$NVM_DIR" ] && [ -r "$NVM_DIR"/bash_completion ];
-then
-  . "$NVM_DIR"/bash_completion
+if [[ -n "${NVM_DIR:-}" && -s "${NVM_DIR}/bash_completion" ]]; then
+	# shellcheck disable=SC1091
+	source "${NVM_DIR}/bash_completion"
 fi
diff --git a/completion/available/openshift.completion.bash b/completion/available/openshift.completion.bash
index 1e7b681506..05b505119c 100644
--- a/completion/available/openshift.completion.bash
+++ b/completion/available/openshift.completion.bash
@@ -1 +1,16 @@
-_command_exists oc && source <(oc completion bash)
+# shellcheck shell=bash
+
+# Make sure oc is installed
+if ! _binary_exists oc; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
+fi
+
+# Don't handle completion if it's already managed
+if _completion_exists oc; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# shellcheck disable=SC1090
+source <(oc completion bash)
diff --git a/completion/available/packer.completion.bash b/completion/available/packer.completion.bash
index 2301f0f226..cfae87006f 100644
--- a/completion/available/packer.completion.bash
+++ b/completion/available/packer.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "packer completion"
 
-if _binary_exists packer; then
-	complete -C packer packer
+# Make sure packer is installed
+if ! _binary_exists packer; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists packer; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+complete -C packer packer
diff --git a/completion/available/pew.completion.bash b/completion/available/pew.completion.bash
index 04e67ecbf5..aa980fd47f 100644
--- a/completion/available/pew.completion.bash
+++ b/completion/available/pew.completion.bash
@@ -1,6 +1,16 @@
 # shellcheck shell=bash
 
-if _command_exists pew
-then
-	source "$(pew shell_config)"
+# Make sure docker is installed
+if ! _binary_exists docker; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists docker; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+# shellcheck disable=SC1090
+source "$(pew shell_config)"
diff --git a/completion/available/pipenv.completion.bash b/completion/available/pipenv.completion.bash
index 4adfab9595..1f3e082e4d 100644
--- a/completion/available/pipenv.completion.bash
+++ b/completion/available/pipenv.completion.bash
@@ -1,4 +1,15 @@
 # shellcheck shell=bash
-if _command_exists pipenv; then
-	eval "$(_PIPENV_COMPLETE=bash_source pipenv)"
+
+# Make sure pipenv is installed
+if ! _binary_exists pipenv; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists pipenv; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+eval "$(_PIPENV_COMPLETE=bash_source pipenv)"
diff --git a/completion/available/rustup.completion.bash b/completion/available/rustup.completion.bash
index 1cf8bc95b4..751cd96bb1 100644
--- a/completion/available/rustup.completion.bash
+++ b/completion/available/rustup.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
+about-completion "rustup (Rust toolchain installer) completion"
 
-# rustup (Rust toolchain installer) completion
+# Make sure rustup is installed
+if ! _binary_exists rustup; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
+fi
 
-if _binary_exists rustup; then
-	eval "$(rustup completions bash)"
+# Don't handle completion if it's already managed
+if _completion_exists rustup; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
 fi
+
+eval "$(rustup completions bash)"
diff --git a/completion/available/rvm.completion.bash b/completion/available/rvm.completion.bash
index cd8ded0468..b00f0b6e1d 100644
--- a/completion/available/rvm.completion.bash
+++ b/completion/available/rvm.completion.bash
@@ -1,5 +1,8 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 # Bash completion support for  RVM.
 # Source: https://rvm.io/workflow/completion
 
-[[ -r $rvm_path/scripts/completion ]] && . $rvm_path/scripts/completion
+if [[ -n "${rvm_path:-}" && -s "${rvm_path}/scripts/completion" ]]; then
+	# shellcheck disable=SC1091
+	source "${rvm_path}/scripts/completion"
+fi
diff --git a/completion/available/svn.completion.bash b/completion/available/svn.completion.bash
index 2f0a23fe97..df8cf7e8a3 100644
--- a/completion/available/svn.completion.bash
+++ b/completion/available/svn.completion.bash
@@ -3,7 +3,9 @@
 # Locate and load completions for `svn`.
 
 # Make sure svn is installed
-_command_exists svn || return
+if ! _binary_exists svn; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+fi
 
 # Don't handle completion if it's already managed
 if _completion_exists svn; then
diff --git a/completion/available/terraform.completion.bash b/completion/available/terraform.completion.bash
index 1452fca8b2..5c2a29767c 100644
--- a/completion/available/terraform.completion.bash
+++ b/completion/available/terraform.completion.bash
@@ -1,10 +1,16 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 
 # Make sure terraform is installed
-_command_exists terraform || return
+if ! _binary_exists terraform; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
+fi
 
 # Don't handle completion if it's already managed
-complete -p terraform &>/dev/null && return
+if _completion_exists terraform; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
 
 # Terraform completes itself
 complete -C terraform terraform
diff --git a/completion/available/todo.completion.bash b/completion/available/todo.completion.bash
index b5517d8654..7281a7e893 100644
--- a/completion/available/todo.completion.bash
+++ b/completion/available/todo.completion.bash
@@ -1,2 +1,3 @@
+# shellcheck shell=bash
 _log_warning 'Bash completion for "todo.txt-cli" is now deprecated, as it used code with incompatible license.
 Please disable this completion and use the instructions from "todo.txt-cli" developers instead.'
diff --git a/completion/available/travis.completion.bash b/completion/available/travis.completion.bash
index 49d8f2cc92..eb3062beb4 100644
--- a/completion/available/travis.completion.bash
+++ b/completion/available/travis.completion.bash
@@ -1,10 +1,18 @@
 # shellcheck shell=bash
 
-if _command_exists travis
-then
-  if [[ -s "${__TRAVIS_COMPLETION_SCRIPT:=${TRAVIS_CONFIG_PATH:-${HOME}/.travis}/travis.sh}" ]]
-	then
-		source "${__TRAVIS_COMPLETION_SCRIPT}"
-	fi
-  unset __TRAVIS_COMPLETION_SCRIPT
+# Make sure travis is installed
+if ! _binary_exists travis; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists travis; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+if [[ -s "${_travis_bash_completion_script:=${TRAVIS_CONFIG_PATH:-${HOME}/.travis}/travis.sh}" ]]; then
+	# shellcheck disable=SC1090
+	source "${_travis_bash_completion_script}"
+fi
+unset "${!_travis_bash_completion@}"
diff --git a/completion/available/vault.completion.bash b/completion/available/vault.completion.bash
index 9520f166b1..ed5f5d297a 100644
--- a/completion/available/vault.completion.bash
+++ b/completion/available/vault.completion.bash
@@ -1,7 +1,16 @@
 # shellcheck shell=bash
-cite "about-completion"
 about-completion "vault completion"
 
-if _binary_exists vault; then
-	complete -C vault vault
+# Make sure vault is installed
+if ! _binary_exists vault; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+	return 1
 fi
+
+# Don't handle completion if it's already managed
+if _completion_exists vault; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+complete -C vault vault
diff --git a/completion/available/virsh.completion.bash b/completion/available/virsh.completion.bash
index 6450b4a305..beab7f0b3c 100644
--- a/completion/available/virsh.completion.bash
+++ b/completion/available/virsh.completion.bash
@@ -1,2 +1,3 @@
+# shellcheck shell=bash
 _log_warning 'Bash completion for "virsh" is now deprecated, as it used code with incompatible license.
 Please disable this completion and use the instructions from "virsh" developers instead.'
diff --git a/completion/available/wpscan.completion.bash b/completion/available/wpscan.completion.bash
index 105468a356..27ea793e48 100644
--- a/completion/available/wpscan.completion.bash
+++ b/completion/available/wpscan.completion.bash
@@ -1,8 +1,17 @@
 # shellcheck shell=bash
 
-_command_exists wpscan || return
+# Make sure wpscan is installed
+if ! _binary_exists wpscan; then
+	_log_warning "Without '$_' installed, this completion won't be too useful."
+fi
 
-function __wpscan_completion() {
+# Don't handle completion if it's already managed
+if _completion_exists wpscan; then
+	_log_warning "completion already loaded - this usually means it is safe to stop using this completion"
+	return 0
+fi
+
+function __wpscan() {
 	local _opt_
 	local OPTS=('--help' '--hh' '--version' '--url' '--ignore-main-redirect' '--verbose' '--output' '--format' '--detection-mode' '--scope' '--headers' '--user-agent' '--vhost' '--random-user-agent' '--user-agents-list' '--http-auth' '--max-threads' '--throttle' '--request-timeout' '--connect-timeout' '--disable-tlc-checks' '--proxy' '--proxy-auth' '--cookie-string' '--cookie-jar' '--cache-ttl' '--clear-cache' '--server' '--cache-dir' '--update' '--no-update' '--wp-content-dir' '--wp-plugins-dir' '--wp-version-detection' '--main-theme-detection' '--enumerate' '--exclude-content-based' '--plugins-list' '--plugins-detection' '--plugins-version-all' '--plugins-version-detection' '--themes-list' '--themes-detection' '--themes-version-all' '--themes-version-detection' '--timthumbs-list' '--timthumbs-detection' '--config-backups-list' '--config-backups-detection' '--db-exports-list' '--db-exports-detection' '--medias-detection' '--users-list' '--users-detection' '--passwords' '--usernames' '--multicall-max-passwords' '--password-attack' '--stealthy')
 	COMPREPLY=()
@@ -13,4 +22,4 @@ function __wpscan_completion() {
 	done
 }
 
-complete -F __wpscan_completion wpscan
+complete -F __wpscan wpscan