Replace usage of the '[' Bash builtin with '[['

There's no benefit to using the POSIX-style '[' test builtin
considering its '-a' and '-o' operators are unused in the Libreboot
build system.  Plus, '[[' is safer with respect to any containing file
redirections (for example).

Prior, both '[' and '[[' were used throughout the codebase--a
disparity in usage which this change aims to eliminate.

4 files changed, 99 insertions, 99 deletions

diff --git a/libs/common b/libs/common
index 750886db..b7a7022e 100755
--- a/libs/common
+++ b/libs/common
@@ -155,7 +155,7 @@ file_checksum_check() {
 	local name=$( basename "$path" )
 	local directory_path=$( dirname "$path" )
 
-	if ! [ -f "$checksum_path" ]
+	if ! [[ -f "$checksum_path" ]]
 	then
 		printf 1>&2 '%s\n' 'Could not verify file checksum!'
 		return 1
@@ -172,7 +172,7 @@ file_signature_create() {
 
 	local signature_path="$path.$DSIG"
 
-	if [ -z "$RELEASE_KEY" ]
+	if [[ -z "$RELEASE_KEY" ]]
 	then
 		return 0
 	fi
@@ -185,7 +185,7 @@ file_signature_check() {
 
 	local signature_path="$path.$DSIG"
 
-	if ! [ -f "$signature_path" ]
+	if ! [[ -f "$signature_path" ]]
 	then
 		printf 1>&2 '%s\n' 'Could not verify file signature!'
 		return 1
@@ -217,7 +217,7 @@ file_exists_check() {
 directory_filled_check() {
 	local path=$1
 
-	if [ -z "$( ls -A "$path" 2> /dev/null )" ]
+	if [[ -z "$( ls -A "$path" 2> /dev/null )" ]]
 	then
 		return 1
 	else
@@ -381,7 +381,7 @@ requirements() {
 	do
 		requirement_path=$( which "$requirement" || true )
 
-		if [ -z "$requirement_path" ]
+		if [[ -z "$requirement_path" ]]
 		then
 			printf 1>&2 '%s\n' "Missing requirement: $requirement"
 			exit 1
@@ -398,7 +398,7 @@ requirements_root() {
 		# We need to keep stdout output to show the command.
 		requirement_path=$( execute_root which "$requirement" || true )
 
-		if [ -z "$requirement_path" ]
+		if [[ -z "$requirement_path" ]]
 		then
 			printf 1>&2 '%s\n' "Missing requirement: $requirement"
 			exit 1
@@ -414,7 +414,7 @@ arguments_concat() {
 
 	for argument in "$@"
 	do
-		if ! [ -z "$concat" ]
+		if ! [[ -z "$concat" ]]
 		then
 			concat="$concat""$delimiter""$argument"
 		else
@@ -432,7 +432,7 @@ execute_root() {
 	printf 1>&2 '%s' 'Running command as root: '
 	printf 1>&2 '%b\n' "$*"
 
-	if ! [ -z "$sudo" ]
+	if ! [[ -z "$sudo" ]]
 	then
 		sudo "$@"
 	else
diff --git a/libs/git b/libs/git
index decdfe01..fdf4d753 100755
--- a/libs/git
+++ b/libs/git
@@ -63,7 +63,7 @@ git_branch_create() {
 		cd "$repository_path"
 		git checkout -B "$branch"
 
-		if ! [ -z "$revision" ]
+		if ! [[ -z "$revision" ]]
 		then
 			git reset --hard "$revision"
 		fi
@@ -96,13 +96,13 @@ git_branch_check() {
 
 	(
 		cd "$repository_path" 2> /dev/null > /dev/null
-		if [ $? -ne 0 ]
+		if [[ $? -ne 0 ]]
 		then
 			return 1
 		fi
 
 		git rev-parse --verify "$branch" 2> /dev/null > /dev/null
-		if [ $? -ne 0 ]
+		if [[ $? -ne 0 ]]
 		then
 			return 1
 		fi
@@ -123,13 +123,13 @@ git_fetch_check() {
 
 	(
 		cd "$repository_path" 2> /dev/null > /dev/null
-		if [ $? -ne 0 ]
+		if [[ $? -ne 0 ]]
 		then
 			return 1
 		fi
 
 		local output=$( git fetch --dry-run origin 2>&1 )
-		if ! [ -z "$output" ]
+		if ! [[ -z "$output" ]]
 		then
 			return 1
 		fi
@@ -270,7 +270,7 @@ git_project_clone() {
 		do
 			git_clone "$repository_path" "$url"
 
-			if [ $? -eq 0 ]
+			if [[ $? -eq 0 ]]
 			then
 				return 0
 			fi
@@ -301,7 +301,7 @@ git_project_prepare_blobs() {
 	local blobs_path=$( project_blobs_path "$project" "$@" )
 	local blob
 
-	if ! [ -f "$blobs_path" ]
+	if ! [[ -f "$blobs_path" ]]
 	then
 		return
 	fi
@@ -330,9 +330,9 @@ git_project_prepare_patch() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -344,7 +344,7 @@ git_project_prepare_patch() {
 
 		local revision_path="$configs_path/$path/$REVISION"
 
-		if ! [ -f "$revision_path" ]
+		if ! [[ -f "$revision_path" ]]
 		then
 			continue
 		fi
@@ -353,7 +353,7 @@ git_project_prepare_patch() {
 		prepare_path=$path
 	done
 
-	if ! [ -z "$prepare_branch" ]
+	if ! [[ -z "$prepare_branch" ]]
 	then
 		git_project_patch_recursive "$project" "$repository" "$prepare_branch" "$prepare_path"
 	fi
@@ -376,9 +376,9 @@ git_project_prepare_revision() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -390,7 +390,7 @@ git_project_prepare_revision() {
 
 		local revision_path="$configs_path/$path/$REVISION"
 
-		if ! [ -f "$revision_path" ]
+		if ! [[ -f "$revision_path" ]]
 		then
 			continue
 		fi
@@ -399,7 +399,7 @@ git_project_prepare_revision() {
 		prepare_revision=$( cat "$revision_path" )
 	done
 
-	if ! [ -z "$prepare_branch" ]
+	if ! [[ -z "$prepare_branch" ]]
 	then
 		git_branch_create "$repository_path" "$prepare_branch" "$prepare_revision"
 	fi
@@ -421,9 +421,9 @@ git_project_prepare_check() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -435,7 +435,7 @@ git_project_prepare_check() {
 
 		local revision_path="$configs_path/$path/$REVISION"
 
-		if ! [ -f "$revision_path" ]
+		if ! [[ -f "$revision_path" ]]
 		then
 			continue
 		fi
@@ -443,7 +443,7 @@ git_project_prepare_check() {
 		prepare_branch=$branch
 	done
 
-	if ! [ -z "$prepare_branch" ]
+	if ! [[ -z "$prepare_branch" ]]
 	then
 		git_branch_check "$repository_path" "$prepare_branch"
 	fi
@@ -462,7 +462,7 @@ git_project_prepare_clean() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			branch="$branch-$argument"
 		fi
@@ -475,7 +475,7 @@ git_project_prepare_clean() {
 		prepare_branch=$branch
 	done
 
-	if ! [ -z "$prepare_branch" ]
+	if ! [[ -z "$prepare_branch" ]]
 	then
 		# Let's not worry about missing branches.
 		(
@@ -483,7 +483,7 @@ git_project_prepare_clean() {
 
 			git_branch_delete "$repository_path" "$prepare_branch"
 
-			if [ $? -ne 0 ]
+			if [[ $? -ne 0 ]]
 			then
 				return 0
 			fi
@@ -504,7 +504,7 @@ git_project_checkout() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			branch="$branch-$argument"
 		fi
@@ -517,7 +517,7 @@ git_project_checkout() {
 		checkout_branch=$branch
 	done
 
-	if ! [ -z "$checkout_branch" ]
+	if ! [[ -z "$checkout_branch" ]]
 	then
 		git_branch_checkout "$repository_path" "$checkout_branch"
 		git_submodule_update "$repository_path"
@@ -564,7 +564,7 @@ git_project_release() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			branch="$branch-$argument"
 		fi
@@ -577,7 +577,7 @@ git_project_release() {
 		release_branch=$branch
 	done
 
-	if ! [ -z "$release_branch" ]
+	if ! [[ -z "$release_branch" ]]
 	then
 		local archive_path="$root/$RELEASE/$SOURCES/$project/$release_branch.$ARCHIVE"
 		local sources_path="$root/$SOURCES/$repository"
@@ -605,7 +605,7 @@ git_project_release_check() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			branch="$branch-$argument"
 		fi
@@ -618,13 +618,13 @@ git_project_release_check() {
 		release_branch=$branch
 	done
 
-	if ! [ -z "$release_branch" ]
+	if ! [[ -z "$release_branch" ]]
 	then
 		local archive_path="$root/$RELEASE/$SOURCES/$project/$release_branch.$ARCHIVE"
 
 		file_exists_check "$archive_path"
 
-		if [ $? -ne 0 ]
+		if [[ $? -ne 0 ]]
 		then
 			return 1
 		else
diff --git a/libs/project b/libs/project
index 524e6222..72bd647a 100755
--- a/libs/project
+++ b/libs/project
@@ -39,7 +39,7 @@ project_helper_include() {
 	local project_path=$( project_path "$project" )
 	local include="$project_path/$project-helper"
 
-	if [ -f "$include" ]
+	if [[ -f "$include" ]]
 	then
 		source "$include"
 	fi
@@ -254,7 +254,7 @@ project_sources_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path-$argument"
 		fi
@@ -267,7 +267,7 @@ project_sources_path() {
 		sources_path=$path
 	done
 
-	if ! [ -z "$sources_path" ]
+	if ! [[ -z "$sources_path" ]]
 	then
 		printf '%s\n' "$sources_path"
 		return
@@ -287,7 +287,7 @@ project_sources_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
@@ -300,7 +300,7 @@ project_sources_path() {
 		sources_path=$path
 	done
 
-	if ! [ -z "$sources_path" ]
+	if ! [[ -z "$sources_path" ]]
 	then
 		printf '%s\n' "$sources_path"
 		return
@@ -323,7 +323,7 @@ project_sources_directory_filled_error() {
 
 	local sources_path=$( project_sources_path "$project" "$@" )
 
-	if ! [ -z "$sources_path" ]
+	if ! [[ -z "$sources_path" ]]
 	then
 		printf 1>&2 '%s\n' "Sources directory for project $project (with ${arguments:-no argument}) already exists"
 		return 1
@@ -339,7 +339,7 @@ project_sources_directory_missing_empty_error() {
 
 	local sources_path=$( project_sources_path "$project" "$@" )
 
-	if [ -z "$sources_path" ]
+	if [[ -z "$sources_path" ]]
 	then
 		printf 1>&2 '%s\n' "Sources directory for project $project (with ${arguments:-no argument}) missing or empty"
 		return 1
@@ -358,14 +358,14 @@ project_sources_archive() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path-$argument"
 		fi
 
 		local archive="$path.$ARCHIVE"
 
-		if ! [ -f "$archive" ]
+		if ! [[ -f "$archive" ]]
 		then
 			continue
 		fi
@@ -373,7 +373,7 @@ project_sources_archive() {
 		sources_archive=$archive
 	done
 
-	if ! [ -z "$sources_archive" ]
+	if ! [[ -z "$sources_archive" ]]
 	then
 		printf '%s\n' "$sources_archive"
 	fi
@@ -403,7 +403,7 @@ project_sources_archive_update() {
 	local archive=$( project_sources_archive "$project" "$@" )
 	local destination=$( dirname "$archive" )
 
-	if [ -d "$sources_path" ]
+	if [[ -d "$sources_path" ]]
 	then
 		rm -rf "$sources_path"
 	fi
@@ -420,7 +420,7 @@ project_sources_archive_missing_error() {
 	local arguments="$*"
 
 	local archive=$( project_sources_archive "$project" "$@" )
-	if [ -z "$archive" ] || ! [ -f "$archive" ]
+	if [[ -z "$archive" ]] || ! [[ -f "$archive" ]]
 	then
 		printf 1>&2 '%s\n' "Missing sources archive for $project (with ${arguments:-no argument})"
 		return 1
@@ -434,7 +434,7 @@ project_sources_archive_missing_check() {
 	shift
 
 	local archive=$( project_sources_archive "$project" "$@" )
-	if [ -z "$archive" ] || ! [ -f "$archive" ]
+	if [[ -z "$archive" ]] || ! [[ -f "$archive" ]]
 	then
 		return 0
 	else
@@ -474,9 +474,9 @@ project_blobs_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -486,7 +486,7 @@ project_blobs_path() {
 
 		local blobs_path="$configs_path/$path/$BLOBS"
 
-		if [ -f "$blobs_path" ]
+		if [[ -f "$blobs_path" ]]
 		then
 			printf '%s\n' "$blobs_path"
 			return
@@ -507,9 +507,9 @@ project_blobs_ignore_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -519,7 +519,7 @@ project_blobs_ignore_path() {
 
 		blobs_ignore_path="$configs_path/$path/$BLOBS_IGNORE"
 
-		if [ -f "$blobs_ignore_path" ]
+		if [[ -f "$blobs_ignore_path" ]]
 		then
 			printf '%s\n' "$blobs_ignore_path"
 			return
@@ -542,7 +542,7 @@ project_arguments_targets() {
 
 	targets_path="$targets_path/$TARGETS"
 
-	if [ -f "$targets_path" ]
+	if [[ -f "$targets_path" ]]
 	then
 		cat "$targets_path"
 	fi
@@ -746,9 +746,9 @@ project_build_check() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -758,7 +758,7 @@ project_build_check() {
 
 		configs_install_path="$project_path/$CONFIGS/$path/$INSTALL"
 
-		if ! [ -f "$configs_install_path" ]
+		if ! [[ -f "$configs_install_path" ]]
 		then
 			continue
 		fi
@@ -771,7 +771,7 @@ project_build_check() {
 			# Source may contain a wildcard.
 			path_wildcard_expand "$source_path" | while read -r source_file_path
 			do
-				if ! [ -f "$source_file_path" ] && ! [ -d "$source_file_path" ]
+				if ! [[ -f "$source_file_path" ]] && ! [[ -d "$source_file_path" ]]
 				then
 					false
 				fi
@@ -826,9 +826,9 @@ project_install() {
 	# Install built files first.
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -838,7 +838,7 @@ project_install() {
 
 		configs_install_path="$project_path/$CONFIGS/$path/$INSTALL"
 
-		if ! [ -f "$configs_install_path" ]
+		if ! [[ -f "$configs_install_path" ]]
 		then
 			continue
 		fi
@@ -869,9 +869,9 @@ project_install() {
 	# Install install files then.
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -881,7 +881,7 @@ project_install() {
 
 		install_install_path="$project_path/$INSTALL/$path/$INSTALL"
 
-		if ! [ -f "$install_install_path" ]
+		if ! [[ -f "$install_install_path" ]]
 		then
 			continue
 		fi
@@ -920,9 +920,9 @@ project_install_check() {
 	# Install built files first.
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -932,7 +932,7 @@ project_install_check() {
 
 		configs_install_path="$project_path/$CONFIGS/$path/$INSTALL"
 
-		if ! [ -f "$configs_install_path" ]
+		if ! [[ -f "$configs_install_path" ]]
 		then
 			continue
 		fi
@@ -944,7 +944,7 @@ project_install_check() {
 			destination=$( printf '%s\n' "$rule" | sed "s/$INSTALL_REGEX/\\2/g" )
 			destination_path="$install_path/$destination"
 
-			if ! [ -f "$destination_path" ] && ! [ -d "$destination_path" ]
+			if ! [[ -f "$destination_path" ]] && ! [[ -d "$destination_path" ]]
 			then
 				false
 			fi
@@ -956,9 +956,9 @@ project_install_check() {
 	# Install install files then.
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
-			if [ -z "$path" ]
+			if [[ -z "$path" ]]
 			then
 				path="$argument"
 			else
@@ -968,7 +968,7 @@ project_install_check() {
 
 		install_install_path="$project_path/$INSTALL/$path/$INSTALL"
 
-		if ! [ -f "$install_install_path" ]
+		if ! [[ -f "$install_install_path" ]]
 		then
 			continue
 		fi
@@ -978,7 +978,7 @@ project_install_check() {
 			destination=$( printf '%s\n' "$rule" | sed "s/$INSTALL_REGEX/\\2/g" )
 			destination_path="$install_path/$destination"
 
-			if ! [ -f "$destination_path" ] && ! [ -d "$destination_path" ]
+			if ! [[ -f "$destination_path" ]] && ! [[ -d "$destination_path" ]]
 			then
 				false
 			fi
@@ -1025,7 +1025,7 @@ project_release_path() {
 	local release_path="$root/$RELEASE/$prefix"
 
 	# Special care for tools and systems, that depend on the host arch.
-	if [ "$prefix" = "$SYSTEMS" ] || [ "$prefix" = "$TOOLS" ]
+	if [[ "$prefix" = "$SYSTEMS" ]] || [[ "$prefix" = "$TOOLS" ]]
 	then
 		local machine=$( uname -m )
 
@@ -1088,7 +1088,7 @@ project_release_sources_archive_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path-$argument"
 		fi
@@ -1103,7 +1103,7 @@ project_release_sources_archive_path() {
 		release_path=$path
 	done
 
-	if ! [ -z "$release_path" ]
+	if ! [[ -z "$release_path" ]]
 	then
 		local archive_path="$root/$RELEASE/$SOURCES/$project/$release_path.$ARCHIVE"
 
@@ -1131,7 +1131,7 @@ project_release_sources_archive_exists_check() {
 	shift
 
 	local archive_path=$( project_release_sources_archive_path "$project" "$@" )
-	if [ -z "$archive_path" ] || ! [ -f "$archive_path" ]
+	if [[ -z "$archive_path" ]] || ! [[ -f "$archive_path" ]]
 	then
 		return 1
 	else
@@ -1399,12 +1399,12 @@ project_file_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
 
-		if ! [ -f "$path/$file" ]
+		if ! [[ -f "$path/$file" ]]
 		then
 			continue
 		fi
@@ -1412,7 +1412,7 @@ project_file_path() {
 		file_path="$path/$file"
 	done
 
-	if [ -z "$file_path" ]
+	if [[ -z "$file_path" ]]
 	then
 		return 1
 	fi
@@ -1429,7 +1429,7 @@ project_file_test() {
 project_file_contents() {
 	local file_path=$( project_file_path "$@" )
 
-	if [ -f "$file_path" ]
+	if [[ -f "$file_path" ]]
 	then
 		cat "$file_path"
 	fi
@@ -1450,14 +1450,14 @@ project_file_contents_herit() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
 
 		file_path="$path/$file"
 
-		if ! [ -f "$file_path" ]
+		if ! [[ -f "$file_path" ]]
 		then
 			continue
 		fi
diff --git a/libs/tool b/libs/tool
index f469d0ef..c18ded8b 100755
--- a/libs/tool
+++ b/libs/tool
@@ -37,7 +37,7 @@ tool_helper_include() {
 	local tool_path=$( tool_path "$tool" )
 	local include="$tool_path/$tool-helper"
 
-	if [ -f "$include" ]
+	if [[ -f "$include" ]]
 	then
 		source "$include"
 	fi
@@ -85,7 +85,7 @@ tool_action() {
 
 		tool_action_check "$action" "$tool" "$@"
 
-		if [ $? -eq 0 ]
+		if [[ $? -eq 0 ]]
 		then
 			return 0
 		fi
@@ -104,7 +104,7 @@ tool_action() {
 			"$action" "$@"
 		)
 
-		if [ $? -ne 0 ]
+		if [[ $? -ne 0 ]]
 		then
 			printf 1>&2 '\n%s\n' "Tool $tool $action (with ${arguments:-no argument}) failed"
 			return 1
@@ -138,7 +138,7 @@ tool_action_check() {
 
 		for tool_force in $TOOLS_FORCE
 		do
-			if [ "$tool_force" = "$tool" ]
+			if [[ "$tool_force" = "$tool" ]]
 			then
 				return 1
 			fi
@@ -189,7 +189,7 @@ tool_action_arguments_recursive() {
 	local action_helper_arguments=$( tool_action_helper "arguments" "$tool" "$@" )
 	local argument
 
-	if [ $? -ne 0 ] || [ -z "$action_helper_arguments" ]
+	if [[ $? -ne 0 ]] || [[ -z "$action_helper_arguments" ]]
 	then
 		tool_action "$action" "$tool" "$@"
 	else
@@ -236,7 +236,7 @@ tool_sources_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
@@ -263,7 +263,7 @@ tool_usage_actions() {
 		fi
 	done
 
-	if [ $# -gt 0 ]
+	if [[ $# -gt 0 ]]
 	then
 		printf '\n%s\n' 'Specific actions:'
 
@@ -292,7 +292,7 @@ tool_usage_arguments_recursive() {
 	local action_helper_arguments=$( tool_action_helper "arguments" "$tool" "$@" )
 	local argument
 
-	if ! [ -z "$action_helper_arguments" ]
+	if ! [[ -z "$action_helper_arguments" ]]
 	then
 		printf '%s\n' "$action_helper_arguments" | while read argument
 		do
@@ -317,12 +317,12 @@ tool_file_path() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
 
-		if ! [ -f "$path/$file" ]
+		if ! [[ -f "$path/$file" ]]
 		then
 			continue
 		fi
@@ -330,7 +330,7 @@ tool_file_path() {
 		file_path="$path/$file"
 	done
 
-	if [ -z "$file_path" ]
+	if [[ -z "$file_path" ]]
 	then
 		return 1
 	fi
@@ -347,7 +347,7 @@ tool_file_test() {
 tool_file_contents() {
 	local file_path=$( tool_file_path "$@" )
 
-	if [ -f "$file_path" ]
+	if [[ -f "$file_path" ]]
 	then
 		cat "$file_path"
 	fi
@@ -368,14 +368,14 @@ tool_file_contents_herit() {
 
 	for argument in "" "$@"
 	do
-		if ! [ -z "$argument" ]
+		if ! [[ -z "$argument" ]]
 		then
 			path="$path/$argument"
 		fi
 
 		file_path="$path/$file"
 
-		if ! [ -f "$file_path" ]
+		if ! [[ -f "$file_path" ]]
 		then
 			continue
 		fi