Fix #115: Speed up the link command.

 - Don't store intermediate `paths` variable; use pipes.
 - Use process substitution to speed up loops.
 - Minor clean-up & fix a few shellcheck warnings.

1 test re: Fail on newline in filename does *NOT* pass.
Is this behavior we need to keep?

lib/commands/link.sh

@@ -11,14 +11,14 @@ function symlink {
 	fi
 	oldIFS=$IFS
 	IFS=$'\n'
-	for filename in $(get_repo_files $repo/home); do
-		remote="$repo/home/$filename"
+	for filename in $(get_repo_files "$repo/home"); do
 		IFS=$oldIFS
+		remote="$repo/home/$filename"
 		local=$HOME/$filename
 
 		if [[ -e $local || -L $local ]]; then
 			# $local exists (but may be a dead symlink)
-			if [[ -L $local && $(readlink "$local") == $remote ]]; then
+			if [[ -L $local && $(readlink "$local") == "$remote" ]]; then
 				# $local symlinks to $remote.
 				if [[ -d $remote && ! -L $remote ]]; then
 					# If $remote is a directory -> legacy handling.
@@ -64,6 +64,37 @@ function symlink {
 	return $EX_SUCCESS
 }
 
+function get_repo_dirs {
+	# Loop through the files tracked by git and compute
+	# a list of their parent directories.
+	# The root of repo we are looking at, will not change.
+	local root=$1
+	# Check if this is the root invocation.
+	if [[ -n $2 ]]; then
+		# The path to the current repo we are looking at:
+		repo_dir="$root/$2"
+		# The relative path to the submodule:
+		relpath="$2/"
+	else
+		# First invocation, the repo_dir is just the root.
+		local repo_dir=$root
+		local relpath=''
+	fi
+	(
+		local path
+		while read path; do
+			printf "%s\n" "$relpath$path"
+			# Get all directory paths up to the root.
+			# We won't ever hit '/' here since ls-files
+			# always shows paths relative to the repo root.
+			while [[ $path =~ '/' ]]; do
+				path=$(dirname "$path")
+				printf "%s\n" "$relpath$path"
+			done
+		done < <(cd "$repo_dir" && git ls-files | xargs -I{} dirname "{}" | sort | uniq)
+	) | sort | uniq
+}
+
 function get_repo_files {
 	# This function descends recursively through all submodules
 	# of a repository and makes the paths returned by `git ls-files`
@@ -72,38 +103,31 @@ function get_repo_files {
 
 	# The root of repo we are looking at, will not change.
 	local root=$1
-	# Check if this is the root invocation
+	# Check if this is the root invocation.
 	if [[ -n $2 ]]; then
-		# The path to the current repo we are looking at
+		# The path to the current repo we are looking at:
 		repo_dir="$root/$2"
-		# The relative path to the submodule
+		# The relative path to the submodule:
 		relpath="$2/"
 	else
-		# First invocation, the repo dir is just the root
+		# First invocation, the repo_dir is just the root.
 		local repo_dir=$root
 		local relpath=''
 	fi
-	local paths=""
-	# Loop through the files tracked by git and compute
-	# a list of their parent directories.
-	for path in $(cd $repo_dir && git ls-files); do
-		# Don't add a newline to the beginning of the list
-		[[ -n $paths ]] && paths="$paths\n"
-		paths="$paths$relpath$path"
-		# Get all directory paths up to the root.
-		# We won't ever hit '/' here since ls-files
-		# always shows paths relative to the repo root.
-		while [[ $path =~ '/' ]]; do
-			path=$(dirname $path)
-			paths="$relpath$path\n$paths"
-		done
-	done
+	(
+		# Get files (+ submodule path prefix).
+		local path
+		while read path; do
+			printf "%s\n" "$relpath$path"
+		done < <(cd "$repo_dir" && git ls-files)
 
-	# Loop through all submodule children (not descendants, i.e. immediate children)
-	# and invoke the function again, passing the relative path to the submodule as the 2nd arg
-	for submodule in $(cd $repo_dir; git submodule --quiet foreach 'printf "%s\n" "$path"'); do
-		paths="$(get_repo_files $root $relpath$submodule)\n$paths"
-	done
+		# Get all directories (+ submodule path prefix).
+		get_repo_files "$repo_dir" "$submodule"
 
-	printf "$paths" | sort | uniq
+		# Recurse on all submodule children (not descendants, i.e. immediate
+		# children), passing the relative path to the submodule as the 2nd arg.
+		for submodule in $(cd "$root"; git submodule --quiet foreach 'printf "%s\n" "$path"'); do
+			get_repo_files "$repo_dir" "$submodule"
+		done
+	) | sort | uniq
 }