diff --git a/go-core.bash b/go-core.bash
index 61cf511..ae66fdc 100755
--- a/go-core.bash
+++ b/go-core.bash
@@ -26,11 +26,14 @@
 #           https://mike-bland.com/
 #           https://github.com/mbland
 
+_GO_EC_GENERR="${_GO_EC_GENERR:-70}"
+_GO_EC_DEPMISS="${_GO_EC_DEPMISS:-72}"
+
 if [[ "${BASH_VERSINFO[0]}" -lt '3' ||
     ( "${BASH_VERSINFO[0]}" -eq '3' && "${BASH_VERSINFO[1]}" -lt '2' ) ]]; then
   printf "This module requires bash version 3.2 or greater:\n  %s %s\n" \
     "$BASH" "$BASH_VERSION"
-  exit 1
+  exit "$_GO_EXIT_DEPMISS"
 fi
 
 # The version of the framework
@@ -46,7 +49,7 @@ declare -r -x _GO_CORE_VERSION='v1.7.0'
 declare -r -x _GO_CORE_URL='https://github.com/mbland/go-script-bash'
 
 declare __go_orig_dir="$PWD"
-cd "${0%/*}" || exit 1
+cd "${0%/*}" || exit "$_GO_EC_GENERR"
 
 # Path to the project's root directory
 #
@@ -56,21 +59,23 @@ cd "${0%/*}" || exit 1
 declare -x _GO_ROOTDIR="$PWD"
 
 if [[ "${BASH_SOURCE[0]:0:1}" != '/' ]]; then
-  cd "$__go_orig_dir/${BASH_SOURCE[0]%/*}" || exit 1
+  cd "$__go_orig_dir/${BASH_SOURCE[0]%/*}" || exit "$_GO_EC_GENERR"
 else
-  cd "${BASH_SOURCE[0]%/*}" || exit 1
+  cd "${BASH_SOURCE[0]%/*}" || exit "$_GO_EC_GENERR"
 fi
 
 # Path to the ./go script framework's directory
 declare -r -x _GO_CORE_DIR="$PWD"
 
+. "$_GO_CORE_DIR/lib/internal/sysexits"
+
 # Set _GO_STANDALONE if your script is a standalone program.
 #
 # See the "Standalone mode" section of README.md for more information.
 if [[ -z "$_GO_STANDALONE" ]]; then
-  cd "$_GO_ROOTDIR" || exit 1
+  cd "$_GO_ROOTDIR" || exit "$_GO_EC_GENERR"
 else
-  cd "$__go_orig_dir" || exit 1
+  cd "$__go_orig_dir" || exit "$_GO_EC_GENERR"
 fi
 unset __go_orig_dir
 
@@ -193,6 +198,8 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
     done
     printf '%s' "$line"
   done <<<"${result//$'\n'/$'\n\x1f'}"$'\x1f'
+
+  return "$_GO_EC_OK"
 }
 
 # Prints the stack trace at the point of the call.
@@ -205,17 +212,17 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
 #   skip_callers:  The number of callers to skip over when printing the stack
 @go.print_stack_trace() {
   local skip_callers="$1"
-  local result=0
+  local result="$_GO_EC_OK"
   local i
 
   if [[ -n "$skip_callers" && ! "$skip_callers" =~ ^[1-9][0-9]*$ ]]; then
     printf '%s argument %s not a positive integer; printing full stack\n' \
       "$FUNCNAME" "'$skip_callers'" >&2
-    result=1
+    result="$_GO_EC_GENERR"
   elif [[ "$skip_callers" -ge "${#FUNCNAME[@]}" ]]; then
     printf '%s argument %d exceeds stack size %d; printing full stack\n' \
       "$FUNCNAME" "$skip_callers" "$((${#FUNCNAME[@]} - 1))" >&2
-    result=1
+    result="$_GO_EC_GENERR"
   fi
 
   if [[ "$result" -ne '0' ]]; then
@@ -263,15 +270,15 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
 #   search_func:  Helper function implementing the search operation
 #
 # Returns:
-#   Zero if `search_func` ever returns zero, nonzero otherwise
+#   _GO_EC_OK if `search_func` ever returns zero, _GO_EC_GENERR otherwise
 @go.search_plugins() {
   local __gsp_plugins_dir="$_GO_SCRIPTS_DIR/plugins"
 
   while true; do
     if "$1" "$__gsp_plugins_dir"; then
-      return
+      return "$_GO_EC_OK"
     elif [[ "$__gsp_plugins_dir" == "$_GO_PLUGINS_DIR" ]]; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
     __gsp_plugins_dir="${__gsp_plugins_dir%/plugins/*}/plugins"
   done
@@ -289,7 +296,7 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
   case "$cmd" in
   '')
     _@go.source_builtin 'help' 1>&2
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   -h|-help|--help)
     cmd='help'
@@ -297,12 +304,12 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
   -*)
     @go.printf "Unknown flag: $cmd\n\n"
     _@go.source_builtin 'help' 1>&2
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   edit)
     if [[ -z "$EDITOR" ]]; then
       echo "Cannot edit $@: \$EDITOR not defined."
-      return 1
+      return "$_GO_EC_CONFIG"
     fi
     "$EDITOR" "$@"
     return
@@ -314,7 +321,7 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
   cd|pushd|unenv)
     @go.printf "$cmd is only available after using \"$_GO_CMD env\" %s\n" \
       "to set up your shell environment." >&2
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   esac
 
@@ -329,7 +336,7 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
   local __go_argv
 
   if ! _@go.set_command_path_and_argv "$cmd" "$@"; then
-    return 1
+    return "$_GO_EC_GENERR"
   fi
 
   if [[ "${__go_cmd_path#$_GO_SCRIPTS_DIR}" =~ /plugins/[^/]+/bin/ ]]; then
@@ -366,7 +373,7 @@ _@go.run_command_script() {
     @go.printf \
       "The first line of %s does not contain #!/path/to/interpreter.\n" \
       "$cmd_path" >&2
-    return 1
+    return "$_GO_EC_BADFRMT"
   fi
 
   interpreter="${interpreter%$'\r'}"
@@ -383,7 +390,7 @@ _@go.run_command_script() {
     . "$cmd_path" "$@"
   elif [[ -z "$interpreter" ]]; then
     @go.printf "Could not parse interpreter from first line of $cmd_path.\n" >&2
-    return 1
+    return "$_GO_EC_BADFRMT"
   else
     if [[ -z "$_GO_CMD_NAME" ]]; then
       local origIFS="$IFS"
@@ -401,23 +408,26 @@ _@go.set_scripts_dir() {
 
   if [[ "$#" -ne '1' ]]; then
     echo "ERROR: there should be exactly one command script dir specified" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   elif [[ ! -e "$scripts_dir" ]]; then
     echo "ERROR: command script directory $scripts_dir does not exist" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   elif [[ ! -d "$scripts_dir" ]]; then
     echo "ERROR: $scripts_dir is not a directory" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   elif [[ ! -r "$scripts_dir" || ! -x "$scripts_dir" ]]; then
     echo "ERROR: you do not have permission to access the $scripts_dir" \
       "directory" >&2
-    return 1
+    return "$_GO_EC_NOPERM"
   fi
   _GO_SCRIPTS_DIR="$scripts_dir"
+  return "$_GO_EC_OK"
 }
 
-if ! _@go.set_scripts_dir "$@"; then
-  exit 1
+_@go.set_scripts_dir "$@" && ec=0 || ec="$?"
+
+if [[ "$ec" -ne "$_GO_EC_OK" ]]; then
+  exit "$ec"
 elif [[ -z "$COLUMNS" ]]; then
   # On Travis, $TERM is set to 'dumb', but `tput cols` still fails.
   if command -v tput >/dev/null && tput cols >/dev/null 2>&1; then
diff --git a/go-template b/go-template
index fe51f57..2e54f3c 100755
--- a/go-template
+++ b/go-template
@@ -57,7 +57,7 @@ download_go_script_bash_tarball() {
 
   if [[ "$protocol" == "$url" ]]; then
     printf 'GO_SCRIPT_BASH_DOWNLOAD_URL has no protocol: %s\n' "$url" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   elif [[ "$(git --version)" =~ windows && "$protocol" == 'file' ]]; then
     url="file://$(cygpath -m "${url#file://}")"
   fi
@@ -74,28 +74,28 @@ download_go_script_bash_tarball() {
     download_cmd=(wget -O - "$url")
   else
     printf "Failed to find cURL, wget, or fetch\n" >&2
-    return 1
+    return "$_GO_EC_DEPMISS"
   fi
 
   if ! command -v tar >/dev/null; then
     printf "Failed to find tar\n" >&2
-    return 1
+    return "$_GO_EC_DEPMISS"
   fi
   printf "Downloading framework from '%s'...\n" "$url"
 
   if ! "${download_cmd[@]}" | tar -xzf - ||
     [[ "${PIPESTATUS[0]}" -ne '0' ]]; then
     printf "Failed to download from '%s'.\n" "$url" >&2
-    return 1
+    return "$_GO_EC_NOTFND"
   elif [[ ! -d "$core_dir_parent" ]] && ! mkdir -p "$core_dir_parent" ; then
     printf "Failed to create scripts dir '%s'\n" "$core_dir_parent" >&2
     rm -rf "$unpacked_dir"
-    return 1
+    return "$_GO_EC_CANTCREAT"
   elif ! mv "$unpacked_dir" "$GO_SCRIPT_BASH_CORE_DIR"; then
     printf "Failed to install downloaded directory in '%s'\n" \
       "$GO_SCRIPT_BASH_CORE_DIR" >&2
     rm -rf "$unpacked_dir"
-    return 1
+    return "$_GO_EC_CANTCREAT"
   fi
   printf "Download of '%s' successful.\n\n" "$url"
 }
@@ -106,7 +106,7 @@ git_clone_go_script_bash() {
       -b "$GO_SCRIPT_BASH_VERSION" "$GO_SCRIPT_BASH_REPO_URL" \
       "$GO_SCRIPT_BASH_CORE_DIR"; then
     printf "Failed to clone '%s'; aborting.\n" "$GO_SCRIPT_BASH_REPO_URL" >&2
-    return 1
+    return "$_GO_EC_GENERR"
   fi
   printf "Clone of '%s' successful.\n\n" "$GO_SCRIPT_BASH_REPO_URL"
 }
@@ -115,7 +115,7 @@ if [[ ! -e "$GO_SCRIPT_BASH_CORE_DIR/go-core.bash" ]]; then
   if ! download_go_script_bash_tarball; then
     printf "Using git clone as fallback\n"
     if ! git_clone_go_script_bash; then
-      exit 1
+      exit "$_GO_EC_GENERR"
     fi
   fi
 fi
diff --git a/lib/bats-main b/lib/bats-main
index 74ec0b1..f977b50 100644
--- a/lib/bats-main
+++ b/lib/bats-main
@@ -180,7 +180,7 @@ fi
   if [[ "$word_index" -eq '0' ]]; then
     echo '--coverage' '--edit' '--list'
     if [[ "${1:0:1}" == '-' ]]; then
-      return
+      return "$_GO_EC_OK"
     fi
   fi
   @go 'glob' '--complete' "$test_word_index" "${_GO_BATS_GLOB_ARGS[@]}" "$@"
diff --git a/lib/bats/helpers b/lib/bats/helpers
index 76a281a..c4619a7 100644
--- a/lib/bats/helpers
+++ b/lib/bats/helpers
@@ -287,7 +287,7 @@ test_break_after_num_iterations() {
     for __tbani_caller_var in "${@:2}"; do
       printf -- '%s: %s\n' "$__tbani_caller_var" "${!__tbani_caller_var}" >&2
     done
-    exit 1
+    exit "$_GO_EC_GENERR"
   fi
 }
 export -f test_break_after_num_iterations
@@ -551,7 +551,7 @@ __create_bats_test_script() {
 
   if [[ -z "$script_path" ]]; then
     echo "No test script name or path specified" >&2
-    exit 1
+    exit "$_GO_EC_USAGE"
   elif [[ "$script_dir" == "$script_path" ]]; then
     script_dir=''
   fi
diff --git a/lib/complete b/lib/complete
index 50f492a..6414a38 100644
--- a/lib/complete
+++ b/lib/complete
@@ -28,7 +28,12 @@
 
   compgen_exit_index="$((${#compreply[@]} - 1))"
 
-  if [[ "${compreply[$compgen_exit_index]}" -ne '0' ]]; then
+  if [[ "${compreply[$compgen_exit_index]}" -eq '1' ]]; then
+    return "$_GO_EC_NOTFND"
+  elif [[ "${compreply[$compgen_exit_index]}" -eq '2' ]]; then
+    return "$_GO_EC_USAGE"
+  elif [[ "${compreply[$compgen_exit_index]}" -ne '0' ]]; then
+    # probably never occurs
     return "${compreply[$compgen_exit_index]}"
   fi
   unset "compreply[$compgen_exit_index]"
@@ -77,4 +82,6 @@
       fi
     done
   done
+
+  return "$_GO_EC_OK"
 }
diff --git a/lib/diff b/lib/diff
index c6f3271..7de34c9 100644
--- a/lib/diff
+++ b/lib/diff
@@ -61,9 +61,9 @@ export _GO_DIFF_EDITOR="${_GO_DIFF_EDITOR:-vimdiff}"
       "$_GO_DIFF_EDITOR" "$lhs" "$rhs"
     fi
   else
-    return '0'
+    return "$_GO_EC_OK"
   fi
-  return '1'
+  return "$_GO_EC_SIGN1"
 }
 
 # Log differences between two directory structures
diff --git a/lib/existence b/lib/existence
index 80d4366..b18180a 100644
--- a/lib/existence
+++ b/lib/existence
@@ -25,10 +25,15 @@
 # Arguments:
 #   label:      Label describing the type of file
 #   file_path:  Path to the file to check
+#
+# Returns:
+#   _GO_EC_OK if file exists, _GO_EC_NOTFND otherwise
 @go.check_file_exists() {
   if [[ ! -e "$2" ]]; then
     @go.printf "%s doesn't exist: %s\n" "$1" "$2" >&2
-    return 1
+    return "$_GO_EC_NOTFND"
+  else
+    return "$_GO_EC_OK"
   fi
 }
 
@@ -37,11 +42,15 @@
 # Arguments:
 #   label:      Label describing the type of file
 #   file_path:  Path to the file to check
+#
+# Returns:
+#   _GO_EC_OK if file exists and is readable, _GO_EC_GENERR otherwise
 @go.check_file_readable() {
   if [[ ! -r "$2" ]]; then
     @go.printf "%s doesn't exist or isn't readable: %s\n" "$1" "$2" >&2
-    return 1
+    return "$_GO_EC_GENERR"
   fi
+  return "$_GO_EC_OK"
 }
 
 # Selects the first installed command from a list of possible commands/names.
@@ -54,18 +63,22 @@
 #   ...:         List of commands from which to select the first available
 #
 # Returns:
-#   Zero if any of the commands are installed, nonzero otherwise
+#   _GO_EC_OK if any of the commands are installed, _GO_EC_NOTFND otherwise
 @go.pick_command() {
   local __go_pick_cmd
   for __go_pick_cmd in "${@:2}"; do
     if command -v "$__go_pick_cmd" >/dev/null; then
-      printf -v "$1" -- '%s' "$__go_pick_cmd"
-      return
+      printf -v "$1" -- '%s' "$__go_pick_cmd" && ec=0 || ec="$?"
+      if [[ "$ec" -ne 0 ]]; then
+        return $((_GO_EC_GENERR+ec))
+      else
+        return "$_GO_EC_OK"
+      fi
     fi
   done
   @go.printf 'None of the following commands were found on the system:\n' >&2
   printf '  %s\n' "${@:2}" >&2
-  return 1
+  return "$_GO_EC_NOTFND"
 }
 
 # Checks whether a required command is installed on the system.
@@ -78,11 +91,13 @@
 #   err_msg:   Name of the command or other info to use in the error message
 #
 # Returns:
-#   Zero if the command is installed, nonzero otherwise
+#   _GO_EC_OK if the command is installed, _GO_EC_DEPMISS otherwise
 @go.check_command_installed() {
-  if ! command -v "$1" >/dev/null; then
+  if command -v "$1" >/dev/null; then
+    return "$_GO_EC_OK"
+  else
     @go.printf 'Please install %s on your system and try again.\n' \
       "${2:-$1}" >&2
-    return 1
+    return "$_GO_EC_DEPMISS"
   fi
 }
diff --git a/lib/file b/lib/file
index a0fc50d..026b334 100644
--- a/lib/file
+++ b/lib/file
@@ -27,7 +27,7 @@ if [[ ! "$_GO_MAX_FILE_DESCRIPTORS" =~ $__GO_FILE_DESCRIPTOR_PATTERN ||
   printf "_GO_MAX_FILE_DESCRIPTORS is %s, must be a number greater than %d.\n" \
     "\"$_GO_MAX_FILE_DESCRIPTORS\"" "$__GO_START_FD" >&2
   @go.print_stack_trace '2' >&2
-  exit 1
+  exit "$_GO_EC_CONFIG"
 fi
 
 . "$_GO_USE_MODULES" 'strings' 'validation'
@@ -80,7 +80,7 @@ fi
   *)
     echo "Unknown mode: $mode" >&2
     @go.print_stack_trace '1' >&2
-    exit 1
+    exit "$_GO_EC_GENERR"
     ;;
   esac
 
@@ -89,16 +89,20 @@ fi
       if ! eval "exec ${i}${bash_mode}${file_path_or_fd}"; then
         echo "Failed to open fd $i for $file_path_or_fd in mode '$mode' at:" >&2
         @go.print_stack_trace '1' >&2
-        exit 1
+        exit "$_GO_EC_ARGERR"
+      fi
+      printf -v "$fd_var_reference" -- '%s' "$i" && ec=0 || ec="$?"
+      if [[ "$ec" -ne 0 ]]; then
+        return $((_GO_EC_GENERR+ec))
+      else
+        return "$_GO_EC_OK"
       fi
-      printf -v "$fd_var_reference" -- '%s' "$i"
-      return
     fi
   done
   echo "No file descriptors < $_GO_MAX_FILE_DESCRIPTORS available; failed at:" \
     >&2
   @go.print_stack_trace '1' >&2
-  exit 1
+  exit "$_GO_EC_NOTFND"
 }
 
 # Calls `printf` on its arguments for each of a list of file descriptors.
@@ -117,7 +121,7 @@ fi
 #   ...:         Arguments to pass to the `printf` builtin
 @go.fds_printf() {
   local output_fds=()
-  local result=0
+  local result="$_GO_EC_OK"
 
   @go.split ',' "$1" 'output_fds'
   shift
@@ -126,7 +130,7 @@ fi
     if [[ ! "$output_fd" =~ $__GO_FILE_DESCRIPTOR_PATTERN ]]; then
       echo "Invalid file descriptor value \"$output_fd\" for $FUNCNAME at:" >&2
       @go.print_stack_trace '1' >&2
-      exit 1
+      exit "$_GO_EC_NOTFND"
     fi
   done
 
@@ -134,7 +138,7 @@ fi
     if ! printf "$@" >&"$output_fd"; then
       echo "Failed to print to fd $output_fd at:" >&2
       @go.print_stack_trace '1' >&2
-      result=1
+      result="$_GO_EC_IOERR"
     fi
   done
   return "$result"
@@ -151,20 +155,20 @@ fi
   if [[ "$#" -eq 0 ]]; then
     echo "No file descriptors to close specified at:" >&2
     @go.print_stack_trace '1' >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   for fd in "$@"; do
     if [[ ! "$fd" =~ $__GO_FILE_DESCRIPTOR_PATTERN ]]; then
       echo "Bad file descriptor \"$fd\" at:" >&2
       @go.print_stack_trace '1' >&2
-      return 1
+      return "$_GO_EC_BADFRMT"
     elif ! eval "exec $fd>&-"; then
       # Believe it or not, this case seems impossible to trigger given the $fd
       # check above. Keeping it despite not being able to cover it with a test.
       echo "Failed to close file descriptor \"$fd\" at:" >&2
       @go.print_stack_trace '1' >&2
-      return 1
+      return "$_GO_EC_GENERR"
     fi
   done
 }
diff --git a/lib/fileutil b/lib/fileutil
index 54c9b2f..61ad798 100644
--- a/lib/fileutil
+++ b/lib/fileutil
@@ -113,7 +113,7 @@
   local __go_source_file_errors=()
   local src
   local dest
-  local result='0'
+  local result="$_GO_EC_OK"
 
   _@go.parse_copy_files_safely_args "$@"
 
@@ -223,7 +223,7 @@ _@go.find_missing_parent_path() {
   __go_missing_parent="$1"
 
   if [[ ! -d "$1" ]]; then
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 }
 
@@ -314,7 +314,7 @@ _@go.set_source_files_for_copy_files_safely() {
   if [[ -n "$__go_src_dir" && "$#" -eq '0' ]]; then
     @go.collect_file_paths "$__go_src_dir"
     __go_src_files=("${__go_collected_file_paths[@]#$__go_src_dir/}")
-    return
+    return "$_GO_EC_OK"
   fi
   __go_src_dir="${__go_src_dir:-$PWD}"
   __go_src_files=()
@@ -337,5 +337,9 @@ _@go.set_source_files_for_copy_files_safely() {
       __go_src_files+=("$canonical_src")
     fi
   done
-  return "${#__go_source_file_errors[@]}"
+
+  if [[ "${#__go_source_file_errors[@]}" -gt 0 ]]; then
+    return "$_GO_EC_GENERR"
+  fi
+  return "$_GO_EC_OK"
 }
diff --git a/lib/internal/argv b/lib/internal/argv
index 296ad20..64684bd 100644
--- a/lib/internal/argv
+++ b/lib/internal/argv
@@ -6,8 +6,10 @@ _@go.check_flag_has_no_arguments() {
 
   if [[ "$#" -ne 0 ]]; then
     echo "ERROR: $flag takes no arguments" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
+
+  return "$_GO_EC_OK"
 }
 
 _@go.check_flag_has_one_argument() {
@@ -16,16 +18,20 @@ _@go.check_flag_has_one_argument() {
 
   if [[ "$#" -eq 0 ]]; then
     echo "ERROR: no argument given after $flag" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   elif [[ "$#" -ne 1 ]]; then
     echo "ERROR: only one argument should follow $flag" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
+
+  return "$_GO_EC_OK"
 }
 
 _@go.check_argv_empty_if_no_flags() {
   if [[ "$#" -ne '0' ]]; then
     echo 'ERROR: with no flag specified, the argument list should be empty' >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
+
+  return "$_GO_EC_OK"
 }
diff --git a/lib/internal/command_descriptions b/lib/internal/command_descriptions
index 11961c8..247715a 100644
--- a/lib/internal/command_descriptions
+++ b/lib/internal/command_descriptions
@@ -19,8 +19,11 @@ _@go.format_summary() {
   printf -v summary "  %-${longest_name_len}s  %s\n" "$cmd_name" "$summary"
 
   if [[ "${#summary}" -le "$COLUMNS" ]]; then
-    printf "$summary"
-    return
+    printf "$summary" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]]; then
+      return $((_GO_EC_GENERR+ec))
+    fi
+    return "$_GO_EC_OK"
   fi
 
   # Pad 4 spaces from first format string, plus 2 more to indent wrapped lines.
@@ -30,7 +33,7 @@ _@go.format_summary() {
 
   if [[ "$padding_size" -ge "$((COLUMNS/2))" ]]; then
     printf "$summary"
-    return
+    return "$_GO_EC_OK"
   fi
   printf -v padding "%-${padding_size}s" ''
 
@@ -71,8 +74,9 @@ _@go.command_summary() {
   local __go_cmd_name
   __go_cmd_desc=''
 
-  if ! _@go.check_command_path_and_parse_command_name "$cmd_path"; then
-    return 1
+  _@go.check_command_path_and_parse_command_name "$cmd_path" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]]; then
+    return "$ec"
   fi
 
   local line
@@ -92,7 +96,7 @@ _@go.command_summary() {
 
   if [[ "$?" -ne '0' ]]; then
     echo "ERROR: problem reading $cmd_path" >&2
-    return 1
+    return "$_GO_EC_GENERR"
   elif [[ -z "$__go_cmd_desc" ]]; then
     __go_cmd_desc='No description available'
   fi
@@ -105,8 +109,9 @@ _@go.command_description() {
   local __go_cmd_name
   __go_cmd_desc=''
 
-  if ! _@go.check_command_path_and_parse_command_name "$cmd_path"; then
-    return 1
+  _@go.check_command_path_and_parse_command_name "$cmd_path" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   fi
 
   local line
@@ -156,7 +161,7 @@ _@go.command_description() {
 
   if [[ "$?" -ne '0' ]]; then
     echo "ERROR: problem reading $cmd_path" >&2
-    return 1
+    return "$_GO_EC_GENERR"
   elif [[ -z "$__go_cmd_desc" ]]; then
     __go_cmd_desc='No description available'
   else
@@ -176,10 +181,10 @@ _@go.check_command_path_and_parse_command_name() {
 
   if [[ -z "$cmd_path" ]]; then
     echo "ERROR: no command script specified" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   elif [[ ! -e "$cmd_path" ]]; then
     echo "ERROR: command script \"$cmd_path\" does not exist" >&2
-    return 1
+    return "$_GO_EC_NOTFND"
   elif [[ "$cmd_path" =~ $subcommand_pattern ]]; then
     __go_cmd_name="${BASH_REMATCH[1]//.d\// }"
   else
diff --git a/lib/internal/commands b/lib/internal/commands
index 46f088f..b72f2f1 100644
--- a/lib/internal/commands
+++ b/lib/internal/commands
@@ -60,7 +60,7 @@ _@go.find_commands() {
   done
 
   if [[ "${#__go_command_scripts[@]}" -eq '0' ]]; then
-    return 1
+    return "$_GO_EC_NOTFND"
   elif [[ -z "$_GO_STANDALONE" ]]; then
     __go_command_scripts=("${__go_command_scripts[@]#$_GO_ROOTDIR/}")
   else
diff --git a/lib/internal/complete b/lib/internal/complete
index a187dd3..64ac1e9 100644
--- a/lib/internal/complete
+++ b/lib/internal/complete
@@ -22,7 +22,7 @@ _@go.complete_top_level_commands() {
 # return status.
 _@go.complete_command_path() {
   if [[ "$#" -eq 0 ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
 
   __go_complete_word_index="$1"
@@ -31,16 +31,16 @@ _@go.complete_command_path() {
 
   if [[ "$#" -le 1 || "$__go_complete_word_index" -eq '0' ]]; then
     _@go.complete_top_level_commands
-    return 1
+    return "$_GO_EC_SIGN1"
   elif ! _@go.set_command_path_and_argv "$@"; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
   (( __go_complete_word_index -= ($# - ${#__go_argv[@]}) ))
 
   if [[ "$__go_complete_word_index" -lt '0' ]]; then
     # This (sub)command itself is the completion target.
     echo "${__go_cmd_path##*/}"
-    return 1
+    return "$_GO_EC_SIGN1"
 
   elif [[ "$__go_complete_word_index" -eq '0' ]]; then
     # Complete subcommand scripts.
diff --git a/lib/internal/path b/lib/internal/path
index e9a5075..063401f 100644
--- a/lib/internal/path
+++ b/lib/internal/path
@@ -10,7 +10,7 @@ _@go.list_available_commands() {
     echo "ERROR: No commands available in:" >&2
     local IFS=$'\n'
     echo "${@/#/  }" >&2
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 
   echo "Available commands are:"
@@ -20,7 +20,7 @@ _@go.list_available_commands() {
 
 _@go.set_command_path_and_argv() {
   if [[ "$#" -eq '0' || -z "$*" ]]; then
-    return 1
+    return "$_GO_EC_ARGERR"
   fi
 
   local cmd_args=("$@")
@@ -38,14 +38,14 @@ _@go.set_command_path_and_argv() {
       break
     elif [[ -e "$try_path" ]]; then
       @go.printf "$try_path is not an executable script\n" >&2
-      return 1
+      return "$_GO_EC_CONFIG"
     fi
   done
 
   if [[ -z "$cmd_path" ]]; then
     printf "Unknown command: ${cmd_name}\n\n" >&2
     _@go.list_available_commands "${_GO_SEARCH_PATHS[@]}" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   local cmd_arg_index=1
@@ -63,7 +63,7 @@ _@go.set_command_path_and_argv() {
       break
     elif [[ ! (-f "$try_path" && -x "$try_path") ]]; then
       @go.printf "$try_path is not an executable script\n" >&2
-      return 1
+      return "$_GO_EC_CONFIG"
     fi
 
     __go_cmd_name+=("$arg")
diff --git a/lib/internal/set-search-paths b/lib/internal/set-search-paths
index b540b39..8b61fec 100644
--- a/lib/internal/set-search-paths
+++ b/lib/internal/set-search-paths
@@ -12,7 +12,7 @@ _@go.set_search_paths_add_plugin_paths() {
       fi
     done
   fi
-  return 1
+  return "$_GO_EC_SIGN1"
 }
 
 _@go.set_search_paths() {
diff --git a/lib/internal/sysexits b/lib/internal/sysexits
new file mode 100644
index 0000000..1a36761
--- /dev/null
+++ b/lib/internal/sysexits
@@ -0,0 +1,75 @@
+#! /bin/bash
+
+declare -r -x -i _GO_EC_OFFSET=0
+# This is useful in case go-script-bash is used together with other frameworks
+# or commands that overlap in their exit codes and the user wants to
+# distinguish among them.
+
+declare -r -x -i _GO_EC_OK=0
+
+declare -r -x -i _GO_EC_GENERR=_GO_EC_OFFSET+64
+# A general error that is not covered by the other exit codes.
+
+declare -r -x -i _GO_EC_EXT1=_GO_EC_OFFSET+65
+declare -r -x -i _GO_EC_EXT2=_GO_EC_OFFSET+66
+# These should be used to return error codes from external commands. Eg when
+# calling `compgen` or `printf`. Most of these commands exit with `1` on general
+# error and `2` on usage error. Their return code should be captured in a
+# a variable, eg `ec`, and returned as `return $((_GO_EC_GENERR+ec)).
+
+declare -r -x -i _GO_EC_USAGE=_GO_EC_OFFSET+67
+# The application was called with an invalid option, parameter, command, etc.
+# This error refers to end-user supplied input to the application, not wrong
+# function arguments, etc.
+
+declare -r -x -i _GO_EC_NOINPUT=_GO_EC_OFFSET+68
+# Some input was expected but none was given. This refers to either expected
+# input from the user (eg via a prompt) or command/function input that is
+# empty (eg an empty file).
+
+declare -r -x -i _GO_EC_BADFRMT=_GO_EC_OFFSET+69
+# An argument or a file is not in the format expected. This is used in
+# validation errors or wrongly formatted files (eg scipts missing the shebang).
+# For bad arguments to functions, _GO_EC_ARGERR should be used.
+
+declare -r -x -i _GO_EC_NOTFND=_GO_EC_OFFSET+70
+# A resource was not found. "Resource" might refer to some file/folder on the
+# filesystem. This return code should also be used by functions that perform a
+# search for the case that no result was found.
+
+declare -r -x -i _GO_EC_ARGERR=_GO_EC_OFFSET+71
+# A function was passed an argument that is invalid. See also _GO_EC_BADFRMT.
+
+declare -r -x -i _GO_EC_DEPMISS=_GO_EC_OFFSET+72
+# A required program is missing.
+
+declare -r -x -i _GO_EC_CANTCREAT=_GO_EC_OFFSET+73
+# An operation failed to create a target. It can be used in filesystem
+# operations like `mv` and `tar x` or in network requests.
+
+declare -r -x -i _GO_EC_IOERR=_GO_EC_OFFSET+74
+# An input/output operation failed. Here, IO is defined loosely. Eg writing to
+# the console failed.
+
+declare -r -x -i _GO_EC_SIGN1=_GO_EC_OFFSET+75
+declare -r -x -i _GO_EC_SIGN2=_GO_EC_OFFSET+76
+# These should not be used as error codes. If a function should return two or
+# three different return values to signal two or three different cases, these
+# _GO_EC_OK should be used to signal the first, most common or expected one and
+# these two signals the rest. Eg, `@go.file_diff` returns _GO_EC_OK if the
+# supplied files are the same or _GO_EC_SIGN1 if not (in both cases, there is no
+# actual error).
+
+declare -r -x -i _GO_EC_NOPERM=_GO_EC_OFFSET+77
+# The user  running the script does not have permission to perform an operation,
+# either locally or over the network.
+
+declare -r -x -i _GO_EC_CONFIG=_GO_EC_OFFSET+78
+# There is an issue with the configuration of either the system, go-script or a
+# network resource. Eg, an environment variable is missing, a set parameter
+# exceeds a maximum value, etc.
+
+declare -r -x -i _GO_EC_BASE=_GO_EC_OFFSET+64
+declare -r -x -i _GO_EC_MAX=_GO_EC_OFFSET+78
+# These are useful in checking whether an exit code belongs to go-script's
+# exit codes.
diff --git a/lib/internal/use b/lib/internal/use
index a5ee0a9..a8a2615 100644
--- a/lib/internal/use
+++ b/lib/internal/use
@@ -87,7 +87,7 @@ _@go.find_module() {
   if [[ -n "$_GO_INJECT_MODULE_PATH" ]]; then
     __go_module_file="$_GO_INJECT_MODULE_PATH/$__go_module_name"
     if [[ -f "$__go_module_file" ]]; then
-      return
+      return "$_GO_EC_OK"
     fi
   fi
   __go_module_file="$_GO_CORE_DIR/lib/$__go_module_name"
@@ -135,7 +135,7 @@ _@go.use_modules() {
     if ! _@go.find_module; then
       @go.printf 'ERROR: Module %s not found at:\n' "$__go_module_name" >&2
       @go.print_stack_trace 1 >&2
-      exit 1
+      exit "$_GO_EC_NOTFND"
     fi
 
     # If we found the module in our project, but we're installed as a plugin,
@@ -176,7 +176,7 @@ _@go.use_modules() {
       @go.printf 'ERROR: Failed to import %s module from %s at:\n' \
         "$__go_module_name" "$__go_module_file" >&2
       @go.print_stack_trace 1 >&2
-      exit 1
+      exit "$_GO_EC_IOERR"
     fi
   done
 }
diff --git a/lib/kcov-ubuntu b/lib/kcov-ubuntu
index fcd79a7..ada0598 100644
--- a/lib/kcov-ubuntu
+++ b/lib/kcov-ubuntu
@@ -54,13 +54,13 @@ run_kcov() {
   if ! command -v apt-get >/dev/null; then
     @go.printf 'Coverage is only available on Linux platforms %s.\n' \
        'with apt-get' >&2
-    return 1
+    return "$_GO_EC_GENERR"
   elif [[ -d "$coverage_dir" ]]; then
     @go.printf '%s %s\n' "The $coverage_dir directory already exists." \
       'Please move or remove this directory first.' >&2
-    return 1
+    return "$_GO_EC_GENERR"
   elif ! ( [[ -f "$kcov_path" ]] || __clone_and_build_kcov "$kcov_dir" ); then
-    return 1
+    return "$_GO_EC_CANTCREAT"
   fi
 
   local kcov_flags=("--include-pattern=$include_pattern"
@@ -86,7 +86,7 @@ run_kcov() {
     fi
   else
     @go.printf 'kcov exited with errors.\n'
-    return 1
+    return "$_GO_EC_GENERR"
   fi
 }
 
@@ -105,7 +105,7 @@ __clone_and_build_kcov() {
     @go.printf 'Cloning kcov repository from %s...\n' "$__KCOV_URL"
 
     if ! @go get git-repo "$__KCOV_URL" "$__KCOV_VERSION" "$kcov_dir"; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
   fi
 
@@ -116,17 +116,17 @@ __clone_and_build_kcov() {
 
     if ! sudo apt-get install -y "${__KCOV_DEV_PACKAGES[@]}"; then
       @go.printf "Failed to install dev packages needed to build kcov." >&2
-      return 1
+      return "$_GO_EC_GENERR"
     fi
   fi
 
   @go.printf 'Building kcov...\n'
 
   if cd "$kcov_dir" >/dev/null && cmake . && make && cd - >/dev/null; then
-    return
+    return "$_GO_EC_OK"
   fi
   @go.printf 'Failed to build kcov.\n' >&2
-  return 1
+  return "$_GO_EC_GENERR"
 }
 
 __check_kcov_dev_packages_installed() {
diff --git a/lib/log b/lib/log
index 793a9a0..8e4a880 100644
--- a/lib/log
+++ b/lib/log
@@ -223,7 +223,7 @@ readonly __GO_LOG_COMMAND_EXIT_PATTERN='^@go.log_command (exit|fatal):([0-9]+)$'
 @go.log() {
   local args=("$@")
   local log_level="${args[0]^^}"
-  local exit_status=0
+  local exit_status="$_GO_EC_OK"
   local log_msg
   local stripped_log_msg
   local level_fd
@@ -235,7 +235,7 @@ readonly __GO_LOG_COMMAND_EXIT_PATTERN='^@go.log_command (exit|fatal):([0-9]+)$'
   if ! _@go.log_level_index "$log_level"; then
     @go.log ERROR "Unknown log level $log_level; defaulting to WARN"
     @go.log WARN "${args[@]}"
-    return 1
+    return "$_GO_EC_GENERR"
   fi
 
   if [[ "$log_level" =~ ERROR|QUIT|FATAL ]]; then
@@ -305,17 +305,26 @@ readonly __GO_LOG_COMMAND_EXIT_PATTERN='^@go.log_command (exit|fatal):([0-9]+)$'
 @go.log_timestamp() {
   _@go.log_init
 
+  local ec=0
+
   case "$__GO_LOG_TIMESTAMP_IMPL" in
   printf)
-    printf -v __go_log_timestamp "%($_GO_LOG_TIMESTAMP_FORMAT)T"
-    return "$?"
+    printf -v __go_log_timestamp "%($_GO_LOG_TIMESTAMP_FORMAT)T" && ec=0 || ec="$?"
     ;;
   date)
-    __go_log_timestamp="$(date "+$_GO_LOG_TIMESTAMP_FORMAT")"
-    return "$?"
+    __go_log_timestamp="$(date "+$_GO_LOG_TIMESTAMP_FORMAT")" && ec=0 || ec="$?"
     ;;
+  *)
+    ec=127
   esac
-  return 1
+
+  if [[ "$ec" -eq 0 ]];then
+    return "$_GO_EC_OK"
+  elif [[ "$ec" -eq 127 ]]; then
+    return "$_GO_EC_DEPMISS"
+  else
+    return "$_GO_EC_GENERR"
+  fi
 }
 
 # Adds a new log level or updates an existing one.
@@ -430,7 +439,7 @@ readonly __GO_LOG_COMMAND_EXIT_PATTERN='^@go.log_command (exit|fatal):([0-9]+)$'
 @go.critical_section_end() {
   if [[ "$__GO_LOG_CRITICAL_SECTION" -ne '0' ]]; then
     ((--__GO_LOG_CRITICAL_SECTION))
-    return 0
+    return "$_GO_EC_OK"
   fi
 }
 
@@ -471,7 +480,7 @@ readonly __GO_LOG_COMMAND_EXIT_PATTERN='^@go.log_command (exit|fatal):([0-9]+)$'
   @go.log RUN "$cmd_string"
 
   if [[ -n "$_GO_DRY_RUN" ]]; then
-    return
+    return "$_GO_EC_OK"
   fi
 
   local __go_log_level_file_descriptors=('1')
@@ -607,7 +616,7 @@ _@go.log_init() {
   local run_fd
 
   if [[ -n "$__GO_LOG_INIT" ]]; then
-    return
+    return "$_GO_EC_OK"
   fi
 
   readonly __GO_LOG_INIT='done'
@@ -701,10 +710,10 @@ _@go.log_level_index() {
   for ((i=0; i != "${#_GO_LOG_LEVELS[@]}"; ++i)); do
     if [[ "${_GO_LOG_LEVELS[$i]}" == "$1" ]]; then
       __go_log_level_index="$i"
-      return
+      return "$_GO_EC_OK"
     fi
   done
-  return 1
+  return "$_GO_EC_NOTFND"
 }
 
 # Checks whether the log message is of sufficient priority to emit
@@ -752,11 +761,11 @@ _@go.log_load() {
   if [[ "${#__GO_LOG_LEVELS_FORMAT_CODES[@]}" != "$num_levels" ]]; then
     echo "Should have $num_levels log level format codes," \
       "only have ${#__GO_LOG_LEVELS_FORMAT_CODES[@]}" >&2
-    exit 1
+    exit "$_GO_EC_CONFIG"
   elif [[ "${#__GO_LOG_LEVELS_FILE_DESCRIPTORS[@]}" != "$num_levels" ]]; then
     echo "Should have $num_levels log level file descriptors," \
       "only have ${#__GO_LOG_LEVELS_FILE_DESCRIPTORS[@]}" >&2
-    exit 1
+    exit "$_GO_EC_CONFIG"
   fi
 }
 
diff --git a/lib/path b/lib/path
index a63a7dd..260b643 100644
--- a/lib/path
+++ b/lib/path
@@ -145,19 +145,19 @@
 
   for current in "${@:2}"; do
     if [[ -e "$current" ]] && ! "$operation" "$current"; then
-      return 1
+      return "$_GO_EC_GENERR"
     elif [[ -d "$current" ]]; then
       if [[ -n "$do_bfs" ]]; then
         bfs_queue+=("$current")
       elif ! @go.walk_file_system "$operation" "$current"/*; then
-        return 1
+        return "$_GO_EC_GENERR"
       fi
     fi
   done
 
   for current in "${bfs_queue[@]}"; do
     if ! @go.walk_file_system '--bfs' "$operation" "$current"/*; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
   done
 }
@@ -191,7 +191,7 @@
   for component in "${components[@]}"; do
     current_path+="${component:-/}"
     if ! "$operation" "$current_path"; then
-      return 1
+      return "$_GO_EC_GENERR"
     elif [[ -n "$component" ]]; then
       current_path+='/'
     fi
@@ -257,7 +257,7 @@
 #   path:  Current path passed in by @go.walk_path_forward
 _@go.realpath_impl() {
   if ! cd -P "$1" >/dev/null 2>&1; then
-    return 1
+    return "$_GO_EC_GENERR"
   fi
   printf -v '__grpi_real_prefix' '%s' "$1"
   printf -v '__grpi_real_dir' '%s' "$PWD"
diff --git a/lib/platform b/lib/platform
index e749d9f..8dbc952 100644
--- a/lib/platform
+++ b/lib/platform
@@ -22,7 +22,7 @@ _@go.platform_os_release() {
   local value
 
   if [[ ! -f "$__GO_ETC_OS_RELEASE" ]]; then
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 
   while read -r line; do
@@ -65,7 +65,7 @@ _@go.platform_ostype() {
 
 _@go.platform() {
   if [[ -n "$_GO_PLATFORM_ID" ]]; then
-    return
+    return "$_GO_EC_OK"
   elif ! _@go.platform_os_release; then
     _@go.platform_ostype
   fi
diff --git a/lib/prompt b/lib/prompt
index 393a9f4..fba1ab1 100644
--- a/lib/prompt
+++ b/lib/prompt
@@ -60,7 +60,7 @@
 
   if [[ -z "${!1}" && -n "$4" ]]; then
     @go.printf '%s\n' "$4" >&2
-    return 1
+    return "$_GO_EC_NOINPUT"
   fi
 }
 
@@ -89,14 +89,15 @@
   fi
   @go.validate_identifier_or_die 'Input prompt response variable name' "$1"
 
-  if ! @go.prompt_for_input "$@"; then
-    return 1
+  @go.prompt_for_input "$@" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]]; then
+    return "$ec"
   elif [[ "$or_die" == 'true' ]]; then
     @go.validate_input_or_die "$description" "${!1}"
   elif ! @go.validate_input "${!1}"; then
     @go.printf '"%s" is an invalid response, as it contains %s.\n' \
       "${!1}" 'unescaped shell metacharacters or control operators' >&2
-    return 1
+    return "$_GO_EC_BADFRMT"
   fi
 }
 
@@ -127,7 +128,7 @@
     @go.printf 'Invalid `default` parameter "%s" for %s at:\n' \
       "$default" "$FUNCNAME" >&2
     @go.print_stack_trace '1' >&2
-    exit 1
+    exit "$_GO_EC_BADFRMT"
     ;;
   esac
 
@@ -135,9 +136,9 @@
     @go.read_prompt_response 'response' "$default"
 
     if [[ "$response" =~ ^[Yy]([Ee][Ss])?$ ]]; then
-      return 0
+      return "$_GO_EC_OK"
     elif [[ "$response" =~ ^[Nn]([Oo])?$ ]]; then
-      return 1
+      return "$_GO_EC_SIGN1"
     else
       if [[ -n "$response" ]]; then
         @go.printf '\n"%s" is an invalid response.\n' "$response" >&2
diff --git a/lib/subcommands b/lib/subcommands
index 5b731ef..68f34d4 100644
--- a/lib/subcommands
+++ b/lib/subcommands
@@ -19,14 +19,14 @@
 # Returns:
 #   zero on success, nonzero on error (when `_GO_CMD_ARGV` is not empty)
 @go.show_subcommands() {
-  local result='0'
+  local result="$_GO_EC_OK"
   local out_fd='1'
   local cmd_name="${_GO_CMD_NAME[*]}"
 
   if [[ "${#_GO_CMD_ARGV[@]}" -ne 0 ]]; then
     @go.printf '"%s" is not an available subcommand of "%s".\n\n' \
       "${_GO_CMD_ARGV[0]}" "$cmd_name" >&2
-    result='1'
+    result="$_GO_EC_USAGE"
     out_fd='2'
   fi
 
diff --git a/lib/testing/log b/lib/testing/log
index e0a7ac9..432f082 100644
--- a/lib/testing/log
+++ b/lib/testing/log
@@ -54,7 +54,7 @@ export _GO_LOG_TIMESTAMP_FORMAT=
   local __go_log_level_index=0
   if ! _@go.log_level_index "$label"; then
     printf 'Unknown log level label: %s\n' "$label" >&2
-    exit 1
+    exit "$_GO_EC_NOTFND"
   fi
   printf '%s' "${__GO_LOG_LEVELS_FORMATTED[$__go_log_level_index]}"
   restore_bats_shell_options "$?"
@@ -174,7 +174,7 @@ __@go.assert_log_equals() {
 
       if ! shift 2; then
         printf 'ERROR: Wrong number of arguments for log line %d.\n' "$i" >&2
-        return 1
+        return "$_GO_EC_ARGERR"
       fi
     else
       expected+=("$1")
@@ -205,7 +205,7 @@ __@go.parse_log_level_label() {
   fi
 
   if ! _@go.log_level_index "$try_level"; then
-    return 1
+    return "$_GO_EC_NOTFND"
   elif [[ "$level_label" != "$try_level" ]]; then
     __log_level_label="$level_label"
   else
diff --git a/lib/testing/stack-trace b/lib/testing/stack-trace
index dfec99f..5c84257 100644
--- a/lib/testing/stack-trace
+++ b/lib/testing/stack-trace
@@ -104,11 +104,11 @@ __@go.stack_trace_item() {
 
   if [[ -z "$function_name" ]]; then
     printf 'No function name specified for `%s`.\n' "${FUNCNAME[1]}" >&2
-    exit 1
+    exit "$_GO_EC_ARGERR"
   elif [[ "$function_name" =~ ^(main|source)$ && -z "$target_line" ]]; then
     printf 'No target line from `%s` specified for `%s`.\n'  \
       "$function_name" "${FUNCNAME[1]}" >&2
-    exit 1
+    exit "$_GO_EC_ARGERR"
   fi
 
   if [[ "$function_name" == 'main' || "$function_name" == 'source' ]]; then
@@ -163,8 +163,11 @@ __@go.stack_trace_item() {
 
   case "$state" in
   SUCCESS)
-    printf '  %s:%d %s\n' "$filepath" "$lineno" "$function_name"
-    return
+    printf '  %s:%d %s\n' "$filepath" "$lineno" "$function_name" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]]; then
+      return $((_GO_EC_GENERR+ec))
+    fi
+    return "$_GO_EC_OK"
     ;;
   MAIN|FOUND_FUNCTION)
     printf 'Line not found in `%s` from "%s": "%s"\n' \
@@ -174,7 +177,7 @@ __@go.stack_trace_item() {
     printf 'Function `%s` not found in "%s".\n' "$function_name" "$filepath" >&2
     ;;
   esac
-  return '1'
+  return "$_GO_EC_NOTFND"
 }
 
 # Implementation for `@go.set_go_core_stack_trace_components`
@@ -199,7 +202,7 @@ __@go.set_go_core_stack_trace_components() {
       if [[ "$stack_item" =~ $go_core_file ]]; then
         GO_CORE_STACK_TRACE_COMPONENTS+=("$stack_item")
       elif [[ "${#_GO_CORE_STACK_TRACE_COMPONENTS[@]}" -ne '0' ]]; then
-        return
+        return "$_GO_EC_OK"
       fi
     done
     rm "$script" "$TEST_GO_SCRIPTS_DIR/print-stack-trace"
@@ -220,7 +223,7 @@ __@go.count_lines() {
 
   if [[ -z "$result_name" ]]; then
     printf 'No result variable specified for `%s`.\n' "${FUNCNAME[1]}" >&2
-    exit 1
+    exit "$_GO_EC_ARGERR"
   fi
 
   while read line; do
@@ -238,9 +241,9 @@ __@go.count_lines() {
 __@go.check_file_path_specified_and_present() {
   if [[ -z "$1" ]]; then
     printf 'No file specified for `%s`.\n' "${FUNCNAME[1]}" >&2
-    exit 1
+    exit "$_GO_EC_ARGERR"
   elif [[ ! -e "$1" ]]; then
     printf 'Create "%s" before calling `%s`.\n' "$1" "${FUNCNAME[1]}" >&2
-    exit 1
+    exit "$_GO_EC_GENERR"
   fi
 }
diff --git a/lib/validation b/lib/validation
index 9be7e9d..61bd913 100644
--- a/lib/validation
+++ b/lib/validation
@@ -36,7 +36,11 @@ readonly __GO_VALID_IDENTIFIER_PATTERN='^[[:alpha:]_][[:alnum:]_]*$'
 # Returns:
 #   0 on success; nonzero on failure
 @go.validate_input() {
-  [[ ! "$1" =~ $__GO_VALIDATE_INPUT_PATTERN ]]
+  if [[ "$1" =~ $__GO_VALIDATE_INPUT_PATTERN ]]; then
+    return "$_GO_EC_BADFRMT"
+  else
+    return "$_GO_EC_OK"
+  fi
 }
 
 # Wraps `@go.validate_input` to print an error and exit on failure
@@ -56,7 +60,7 @@ readonly __GO_VALID_IDENTIFIER_PATTERN='^[[:alpha:]_][[:alnum:]_]*$'
       "$description" "$value" "${FUNCNAME[$((skip_callers - 1))]}" \
       'unescaped shell metacharacters or control operators' >&2
     @go.print_stack_trace "$skip_callers" >&2
-    exit 1
+    exit "$_GO_EC_BADFRMT"
   fi
 }
 
@@ -70,7 +74,11 @@ readonly __GO_VALID_IDENTIFIER_PATTERN='^[[:alpha:]_][[:alnum:]_]*$'
 # Returns:
 #   0 on success; nonzero on failure
 @go.validate_identifier() {
-  [[ "$1" =~ $__GO_VALID_IDENTIFIER_PATTERN ]]
+  if [[ "$1" =~ $__GO_VALID_IDENTIFIER_PATTERN ]]; then
+    return "$_GO_EC_OK"
+  else
+    return "$_GO_EC_BADFRMT"
+  fi
 }
 
 # Wraps `@go.validate_identifier` to print an error and exit on failure
@@ -98,6 +106,6 @@ readonly __GO_VALID_IDENTIFIER_PATTERN='^[[:alpha:]_][[:alnum:]_]*$'
     printf '%s "%s" for %s %s at:\n' \
       "$description" "$value" "$called_func" "$err_msg" >&2
     @go.print_stack_trace "$skip_callers" >&2
-    exit 1
+    exit "$_GO_EC_BADFRMT"
   fi
 }
diff --git a/libexec/aliases b/libexec/aliases
index ecfbbcd..2836527 100755
--- a/libexec/aliases
+++ b/libexec/aliases
@@ -31,14 +31,14 @@ _@go.aliases() {
     for c in "${_GO_ALIAS_CMDS[@]}"; do
       echo "$c"
     done
-    return
+    return "$_GO_EC_OK"
   elif [[ "$1" == '--complete' ]]; then
     # Tab completions
     local word_index="$2"
     if [[ "$word_index" -eq 0 ]]; then
       echo "--exists"
     fi
-    return
+    return "$_GO_EC_OK"
   fi
 
   . "$_GO_CORE_DIR/lib/internal/argv"
@@ -49,17 +49,17 @@ _@go.aliases() {
     flag="${1#--}"
     shift
     if ! _@go.check_flag_has_one_argument "--$flag" "$@"; then
-      return 1
+      return "$_GO_EC_USAGE"
     fi
     ;;
   -*)
     @go.printf "ERROR: unknown flag: $1\n" >&2
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   esac
 
   if [[ -z "$flag" ]] && ! _@go.check_argv_empty_if_no_flags "$@"; then
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   # Help filter
@@ -67,7 +67,7 @@ _@go.aliases() {
     local pattern='{{_GO_ALIAS_CMDS}}'
     local replacement="${_GO_ALIAS_CMDS[@]}"
     echo "${1//$pattern/$replacement}"
-    return
+    return "$_GO_EC_OK"
   fi
 
   for c in "${_GO_ALIAS_CMDS[@]}"; do
@@ -84,10 +84,10 @@ _@go.aliases() {
           "\"$_GO_CMD env\" to set up your shell environment."
       fi
     fi
-    return
+    return "$_GO_EC_OK"
   done
 
-  return 1
+  return "$_GO_EC_NOTFND"
 }
 
 _@go.aliases "$@"
diff --git a/libexec/builtins b/libexec/builtins
index 8cb485d..a99e14e 100755
--- a/libexec/builtins
+++ b/libexec/builtins
@@ -59,8 +59,10 @@ _@go.builtin_summaries() {
   local __go_cmd_desc
 
   for cmd_name in "${_GO_BUILTIN_CMDS[@]}"; do
-    if ! _@go.command_summary "$_GO_CORE_DIR/libexec/$cmd_name"; then
-      return 1
+
+    _@go.command_summary "$_GO_CORE_DIR/libexec/$cmd_name" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]] ; then
+      return "$ec"
     fi
     _@go.format_summary "$cmd_name" "$__go_cmd_desc" $longest_name_len
   done
@@ -70,14 +72,14 @@ _@go.builtins() {
   if [[ "$#" -eq '0' ]]; then
     local IFS=$'\n'
     echo "${_GO_BUILTIN_CMDS[*]}"
-    return
+    return "$_GO_EC_OK"
   elif [[ "$1" == '--complete' ]]; then
     # Tab completions
     local word_index="$2"
     if [[ "$word_index" -eq '0' ]]; then
       echo '--exists' '--summaries'
     fi
-    return
+    return "$_GO_EC_OK"
   fi
 
   . "$_GO_CORE_DIR/lib/internal/argv"
@@ -88,7 +90,7 @@ _@go.builtins() {
     flag="$1"
     shift
     if ! _@go.check_flag_has_no_arguments "$flag" "$@"; then
-      return 1
+      return "$_GO_EC_USAGE"
     fi
     _@go.builtin_summaries
     return
@@ -97,35 +99,35 @@ _@go.builtins() {
     flag="$1"
     shift
     if ! _@go.check_flag_has_one_argument "$flag" "$@"; then
-      return 1
+      return "$_GO_EC_USAGE"
     fi
     for cmd_name in "${_GO_BUILTIN_CMDS[@]}"; do
       if [[ "$cmd_name" == "$1" ]]; then
-        return
+        return "$_GO_EC_OK"
       fi
     done
-    return 1
+    return "$_GO_EC_NOTFND"
     ;;
   --help-filter)
     flag="$1"
     shift
     # Help filter
     if ! _@go.check_flag_has_one_argument "$flag" "$@"; then
-      return 1
+      return "$_GO_EC_USAGE"
     fi
     local pattern='{{_GO_BUILTIN_SUMMARIES}}'
     local replacement="$(_@go.builtin_summaries)"
     echo "${1//$pattern/$replacement}"
-    return
+    return "$_GO_EC_OK"
     ;;
   -*)
     echo "ERROR: unknown flag: $1"
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   esac
 
   if ! _@go.check_argv_empty_if_no_flags "$@"; then
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 }
 
diff --git a/libexec/commands b/libexec/commands
index ad65a5d..6ea3ebb 100755
--- a/libexec/commands
+++ b/libexec/commands
@@ -64,7 +64,7 @@ _@go.commands_parse_search_paths() {
   for search_path in "${__go_commands_search_paths[@]}"; do
     if [[ ! -d "$search_path" ]]; then
       @go.printf "Command search path %s does not exist.\n" "$search_path" >&2
-      return 1
+      return "$_GO_EC_NOTFND"
     fi
   done
 }
@@ -77,7 +77,7 @@ _@go.commands_parse_argv() {
     ;;
   -*)
     echo "Unknown option: $1"
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   esac
 
@@ -86,19 +86,20 @@ _@go.commands_parse_argv() {
   elif [[ "$1" =~ : || -d "$1" ]]; then
     if [[ "$#" -ne 1 ]]; then
       @go.printf 'Cannot specify any arguments after search paths.\n' >&2
-      return 1
+      return "$_GO_EC_USAGE"
     elif ! _@go.commands_parse_search_paths "$1"; then
-      return 1
+      return "$_GO_EC_NOTFND"
     fi
   else
     if _@go.source_builtin 'aliases' --exists "$1"; then
       @go.printf '%s is a shell alias.\n' "$1" >&2
-      return 1
+      return "$_GO_EC_GENERR"
     fi
 
     local __go_cmd_path
-    if ! _@go.set_command_path_and_argv "$@"; then
-      return 1
+    _@go.set_command_path_and_argv "$@" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]]; then
+      return "$?"
     fi
     __go_commands_search_paths=("${__go_cmd_path}.d")
   fi
@@ -111,7 +112,7 @@ _@go.commands_tab_completions() {
   if [[ "$word_index" -eq '0' ]]; then
     echo '--paths' '--summaries'
     if [[ "${1:0:1}" == '-' || "$#" -gt 1 ]]; then
-      return
+      return "$_GO_EC_OK"
     fi
   fi
 
@@ -119,13 +120,13 @@ _@go.commands_tab_completions() {
     shift
     ((--word_index))
   elif [[ "$1" =~ : || -d "$1" ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
 
   local args=("$@")
   local last_arg_index="$((${#args[@]} - 1))"
   if [[ "$word_index" -lt "$last_arg_index" ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
   _@go.commands "${args[@]:0:$word_index}"
 }
@@ -141,8 +142,9 @@ _@go.commands() {
   local __go_commands_action="list"
   local __go_commands_search_paths=()
 
-  if ! _@go.commands_parse_argv "$@"; then
-    return 1
+  _@go.commands_parse_argv "$@" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   fi
 
   . "$_GO_CORE_DIR/lib/internal/commands"
@@ -152,7 +154,7 @@ _@go.commands() {
   local __go_longest_name_len
 
   if ! _@go.find_commands "${__go_commands_search_paths[@]}"; then
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 
   case "$__go_commands_action" in
diff --git a/libexec/complete b/libexec/complete
index 9de742b..c31e5c0 100755
--- a/libexec/complete
+++ b/libexec/complete
@@ -69,6 +69,7 @@ _@go.complete_args() {
   local args=("$@")
   local cmd_name="${args[0]}"
   local word="${args[$word_index]}"
+  local ec=0
 
   . "$_GO_CORE_DIR/lib/internal/complete"
 
@@ -90,6 +91,7 @@ _@go.complete_args() {
     return
   fi
 
+  ec="unset"
   case "$cmd_name" in
   cd|pushd)
     @go.compgen -d -- "$word"
@@ -103,12 +105,12 @@ _@go.complete_args() {
     cmd_name='help'
     ;;
   -*|unenv)
-    return 1
+    return "$_GO_EC_GENERR"
     ;;
   esac
 
   if _@go.source_builtin 'aliases' --exists "$cmd_name"; then
-    @go.compgen -f -- "$word"
+    @go.compgen -f -- "$word" && ec=0 || ec="$?"
     return
   fi
 
diff --git a/libexec/demo-core.d/log b/libexec/demo-core.d/log
index 2b049b3..19fa5db 100755
--- a/libexec/demo-core.d/log
+++ b/libexec/demo-core.d/log
@@ -68,7 +68,7 @@ log_demo() {
     if [[ "$2" -eq 0 ]]; then
       echo "-v --verbose"
     fi
-    return
+    return "$_GO_EC_OK"
   fi
 
   . "$_GO_USE_MODULES" 'log'
diff --git a/libexec/demo-core.d/prompt b/libexec/demo-core.d/prompt
index 6b4e2c9..544dc4d 100755
--- a/libexec/demo-core.d/prompt
+++ b/libexec/demo-core.d/prompt
@@ -18,7 +18,7 @@ _@go.prompt_demo() {
   # No default value; returns error on no input.
   if ! @go.prompt_for_input 'name' $'What is your name?\n' '' \
     'Run away, Sir or Madam Not Appearing in this Film! Run away!'; then
-    return 1
+    return "$_GO_EC_NOINPUT"
   fi
   @go.printf 'Nice to meet you, %s!\n' "$name"
 
@@ -28,7 +28,7 @@ _@go.prompt_demo() {
     @go.prompt_for_input 'quest' $'What is your quest?\n' "$quest"
   elif ! @go.prompt_for_yes_or_no "Might I suggest: $quest" 'yes'; then
     @go.printf 'OK, no quest. Suit yourself!\n'
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
   @go.printf 'Your quest is: %s\n' "$quest"
 }
diff --git a/libexec/demo-core.d/select-option b/libexec/demo-core.d/select-option
index b55789e..7f83a1f 100755
--- a/libexec/demo-core.d/select-option
+++ b/libexec/demo-core.d/select-option
@@ -27,7 +27,7 @@ select_option_demo() {
 
     if ! @go.select_option 'selected' "${options[@]}"; then
       @go.printf 'You declined to select an option. Exiting...\n\n'
-      return 1
+      return "$_GO_EC_NOINPUT"
     else
       @go.printf 'You selected: "%s"\n\n' "$selected"
     fi
@@ -35,7 +35,7 @@ select_option_demo() {
     if ! @go.prompt_for_yes_or_no 'Would you like to select another option?' \
       'yes'; then
       @go.printf 'Exiting...\n'
-      return 0
+      return
     fi
   done
 }
diff --git a/libexec/env b/libexec/env
index 22e52b4..cf93054 100755
--- a/libexec/env
+++ b/libexec/env
@@ -26,7 +26,7 @@ _@go.env() {
     if [[ "$word_index" -eq '0' ]]; then
       echo '-'
     fi
-    return
+    return "$_GO_EC_OK"
   fi
 
   local go_func="$1"
@@ -39,7 +39,7 @@ _@go.env() {
     @go.printf "%s%s\n" \
       "Check $_GO_CORE_URL/tree/master/lib/env to see if an implementation " \
       "has been added, or feel free to send a pull request to add it." >&2
-    return 1
+    return "$_GO_EC_GENERR"
   fi
 
   local spaces_error=('ERROR: %s must not contain spaces in order'
@@ -47,7 +47,7 @@ _@go.env() {
 
   if _@go.has_spaces "$default_name"; then
     @go.printf "${spaces_error[*]}" "the \"$default_name\" script" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   fi
 
   if [[ -z "$go_func" ]]; then
@@ -67,7 +67,7 @@ _@go.env() {
       @go.printf 'ERROR: %s must contain a line of the form "%s" %s%s\n' \
         "$shell_impl" "$eval_pattern" "illustrating the command used to " \
         "evaluate the generated shell commands." >&2
-      return 1
+      return "$_GO_EC_BADFRMT"
     fi
 
     read -r -d '' help_msg <<END_OF_HELP
@@ -84,7 +84,7 @@ END_OF_HELP
 
   if _@go.has_spaces "$go_func"; then
     @go.printf "${spaces_error[*]}" "\"$go_func\"" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   fi
 
   read -r -d '' env_script < "$shell_impl"
diff --git a/libexec/get.d/file b/libexec/get.d/file
index f6fc7a6..dca7351 100755
--- a/libexec/get.d/file
+++ b/libexec/get.d/file
@@ -98,7 +98,7 @@ _@go.get_file_download_command() {
     fi
     @go.printf 'Please install curl or wget before running "%s".\n' \
       "${_GO_CMD_NAME[*]}" >&2
-    return 1
+    return "$_GO_EC_DEPMISS"
     ;;
   esac
 }
@@ -116,27 +116,27 @@ _@go.get_file_impl() {
   local download_dir="$1"
   local filename="$2"
   local url="$3"
-  local result='0'
+  local result="$_GO_EC_OK"
   local errfile="${url##*/}.get-error"
   local errmsg
 
   local __go_get_file_download_cmd=()
   if ! _@go.get_file_download_command "$filename"; then
-    return 1
+    return "$_GO_EC_DEPMISS"
   fi
 
   if [[ -n "$filename" ]]; then
     if [[ -f "$filename" ]]; then
       @go.printf 'File already exists; not overwriting: %s\n' "$filename" >&2
-      return 1
+      return "$_GO_EC_CANTCREAT"
     elif [[ ! -d "$download_dir" ]] && ! mkdir -p "$download_dir"; then
       @go.printf "Download dir doesn't exist and can't be created: %s\n" \
         "$download_dir" >&2
-      return 1
+      return "$_GO_EC_CANTCREAT"
     elif [[ ! -w "$download_dir" ]]; then
       @go.printf "You don't have permission to write to download dir: %s\n" \
         "$download_dir" >&2
-      return 1
+      return "$_GO_EC_NOPERM"
     fi
     errfile="${filename}.get-error"
   fi
@@ -154,7 +154,7 @@ _@go.get_file_impl() {
     if [[ -f "$filename" ]]; then
       rm "$filename"
     fi
-    result='1'
+    result="$_GO_EC_GENERR"
 
   elif [[ -n "$filename" ]]; then
     @go.printf 'Downloaded "%s" as: %s\n' "$url" "$filename"
@@ -186,7 +186,7 @@ _@go.get_file() {
 
   if [[ "$#" -ne '1' ]]; then
     @go help "${_GO_CMD_NAME[@]}" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   url="$1"
diff --git a/libexec/get.d/git-repo b/libexec/get.d/git-repo
index 9064aa8..acb6252 100755
--- a/libexec/get.d/git-repo
+++ b/libexec/get.d/git-repo
@@ -32,13 +32,13 @@ _@go.get_git_repo_impl() {
   if ! command -v git >/dev/null; then
     @go.printf 'Please install git before running "%s".\n' \
       "${_GO_CMD_NAME[*]}" >&2
-    return 1
+    return "$_GO_EC_DEPMISS"
   elif [[ -e "$clone_dir" ]]; then
     @go.printf '"%s" already exists; not updating.\n' "$clone_dir"
-    return 1
+    return "$_GO_EC_GENERR"
   elif ! "${git_clone[@]}" -b "$git_ref" "$repo_url" "$clone_dir"; then
     @go.printf 'Failed to clone %s.\n' "$repo_msg" >&2
-    return 1
+    return "$_GO_EC_IOERR"
   fi
   @go.printf 'Successfully cloned %s.\n' "$repo_msg"
 }
@@ -62,7 +62,7 @@ _@go.get_git_repo() {
 
   if [[ "$#" -ne '3' ]]; then
     @go help "${_GO_CMD_NAME[@]}" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   if [[ -e "$repo_url" ]]; then
diff --git a/libexec/glob b/libexec/glob
index 94217f7..0d8dd2c 100755
--- a/libexec/glob
+++ b/libexec/glob
@@ -52,7 +52,7 @@ _@go.glob_impl() {
   # directory (preferring the file if they share the same name).
   if [[ -f "$pattern$__go_glob_suffix" ]]; then
     __go_glob_matches+=("$pattern$__go_glob_suffix")
-    return
+    return "$_GO_EC_OK"
   elif [[ -d "$pattern" ]]; then
     pattern="${pattern%/}/*"
   fi
@@ -63,7 +63,7 @@ _@go.glob_impl() {
   _@go.glob_impl_helper "$pattern"
 
   if [[ "${#__go_glob_impl_matches[@]}" -eq '0' ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
   __go_glob_matches+=("${__go_glob_impl_matches[@]}")
 }
@@ -119,7 +119,7 @@ _@go.glob_tab_completion_parse_argv() {
 
       if [[ "$word_index" -eq "$((i+1))" ]]; then
         # No completion for the GLOBIGNORE spec.
-        return 1
+        return "$_GO_EC_SIGN1"
       elif [[ "${__go_glob_ignore_spec:0:1}" =~ $shell_quote ]]; then
         # The shell won't expand arguments or remove quotes during completion.
         local spec_len="${#__go_glob_ignore_spec}"
@@ -130,17 +130,17 @@ _@go.glob_tab_completion_parse_argv() {
 
     if [[ "$word_index" -lt "$i" ]]; then
       __go_glob_complete_flags_only='true'
-      return
+      return "$_GO_EC_OK"
     elif [[ -d "$arg" ]]; then
       if [[ "$word_index" -eq "$((i+1))" ]]; then
         # No completion for the file suffix.
-        return 1
+        return "$_GO_EC_SIGN1"
       elif [[ "$word_index" -ne "$i" ]]; then
         # Don't set rootdir if rootdir is the completion target argument.
         __go_glob_rootdir="${arg%/}"
         __go_glob_suffix="${args[$((i+1))]}"
       fi
-      return
+      return "$_GO_EC_OK"
     fi
   done
 }
@@ -178,10 +178,10 @@ _@go.glob_tab_completion() {
   local __go_glob_complete_flags_only
 
   if ! _@go.glob_tab_completion_parse_argv "$@"; then
-    return 1
+    return "$_GO_EC_SIGN1"
   elif [[ "$__go_glob_complete_flags_only" == 'true' ]]; then
     echo "${__go_glob_flags[@]}"
-    return
+    return "$_GO_EC_OK"
   elif [[ -z "$__go_glob_rootdir" ]]; then
     echo "${__go_glob_flags[@]}"
     . "$_GO_USE_MODULES" 'complete'
@@ -195,7 +195,7 @@ _@go.glob_tab_completion() {
   _@go.glob_trim_matches
 
   if [[ "${#__go_glob_matches[@]}" -eq '0' ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   elif [[ "${#__go_glob_matches[@]}" -eq '1' ]]; then
     echo "${__go_glob_matches[0]}"
   else
@@ -209,10 +209,10 @@ _@go.glob_set_globignore() {
 
   if [[ -z "$rootdir" ]]; then
     echo "ERROR: root dir not set before setting GLOBIGNORE" >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   elif [[ ! -d "$rootdir" ]]; then
     echo "ERROR: root dir not valid when setting GLOBIGNORE: $rootdir " >&2
-    return 1
+    return "$_GO_EC_CONFIG"
   fi
 
   if [[ -n "$globignore_spec" ]]; then
@@ -239,7 +239,7 @@ _@go.glob_parse_argv() {
       ;;
     *)
       @go.printf "Unknown flag: $1" >&2
-      return 1
+      return "$_GO_EC_USAGE"
       ;;
     esac
   done
@@ -249,11 +249,11 @@ _@go.glob_parse_argv() {
 
   if [[ -z "$__go_glob_rootdir" ]]; then
     @go.printf "Root directory argument not specified.\n" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   elif [[ ! -d "$__go_glob_rootdir" ]]; then
     @go.printf "Root directory argument %s is not a directory.\n" \
       "$__go_glob_rootdir" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   fi
 
   __go_glob_suffix="$1"
@@ -261,11 +261,11 @@ _@go.glob_parse_argv() {
 
   if [[ -z "$__go_glob_suffix" ]]; then
     @go.printf "File suffix argument not specified.\n" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   fi
 
   if ! _@go.glob_set_globignore "$globignore" "$__go_glob_rootdir"; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
   __go_glob_patterns=("${@:-*}")
 }
@@ -275,7 +275,7 @@ _@go.glob() {
   if [[ "$1" == '--complete' ]]; then
     shift
     _@go.glob_tab_completion "$@"
-    return
+    return "$_GO_EC_OK"
   fi
 
   local __go_glob_trim
@@ -284,7 +284,7 @@ _@go.glob() {
   local __go_glob_patterns
 
   if ! _@go.glob_parse_argv "$@"; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
 
   local pattern
@@ -294,7 +294,7 @@ _@go.glob() {
     if ! _@go.glob_impl "$__go_glob_rootdir/$pattern"; then
       @go.printf "\"$pattern\" does not match any %s files in %s.\n" \
         "$__go_glob_suffix" "$__go_glob_rootdir" >&2
-      return 1
+      return "$_GO_EC_NOTFND"
     fi
   done
 
diff --git a/libexec/help b/libexec/help
index 7c3d207..8611adc 100755
--- a/libexec/help
+++ b/libexec/help
@@ -90,14 +90,15 @@ _@go.usage() {
 
 _@go.help_message_for_command() {
   if _@go.source_builtin 'aliases' --help "$1"; then
-    return
+    return "$_GO_EC_OK"
   fi
 
   local __go_cmd_path
   local __go_argv
 
-  if ! _@go.set_command_path_and_argv "$@"; then
-    return 1
+  _@go.set_command_path_and_argv "$@" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   fi
 
   local cmd_name="${__go_cmd_path//.d\// }"
@@ -111,7 +112,7 @@ _@go.help_message_for_command() {
     # _shouldn't_ ever happen.
     @go.printf "ERROR: failed to parse description from %s\n" \
       "$__go_cmd_path" >&2
-    return 1
+    return "$_GO_EC_BADFRMT"
   fi
 
   local filter_pattern='# [Hh]elp [Ff]ilter['$'\n\r'']'
diff --git a/libexec/modules b/libexec/modules
index 3afe2af..e174ea0 100755
--- a/libexec/modules
+++ b/libexec/modules
@@ -63,10 +63,10 @@ _@go.modules_help() {
     __go_module_file="$_GO_USE_MODULES"
   elif [[ "$#" -ne '1' ]]; then
     @go.printf "Please specify only one module name.\n" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   elif ! _@go.find_module; then
     @go.printf "Unknown module: $1\n" >&2
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 
   local __go_cmd_desc
@@ -76,7 +76,7 @@ _@go.modules_help() {
   if ! _@go.command_description "$__go_module_file"; then
     @go.printf "ERROR: failed to parse description from %s\n" \
       "$__go_module_file" >&2
-    return 1
+    return "$_GO_EC_BADFRMT"
   fi
   @go.printf "$__go_module_name - $__go_cmd_desc\n"
 }
@@ -102,7 +102,7 @@ _@go.modules_summaries() {
   for module_path in "${__go_modules[@]}"; do
     if ! _@go.command_summary "$module_path"; then
       @go.printf "ERROR: failed to parse summary from %s\n" "$module_path" >&2
-      return 1
+      return "$_GO_EC_BADFRMT"
     fi
     __go_modules_summaries+=("$__go_cmd_desc")
   done
@@ -134,7 +134,7 @@ _@go.modules_produce_listing() {
 
   if [[ -z "$action" ]]; then
     __go_modules_listing=("${modules[@]}")
-    return
+    return "$_GO_EC_OK"
   fi
 
   . "$_GO_USE_MODULES" 'format'
@@ -148,7 +148,7 @@ _@go.modules_produce_listing() {
   summaries)
     local __go_modules_summaries=()
     if ! _@go.modules_summaries; then
-      return 1
+      return "$_GO_EC_BADFRMT"
     fi
     @go.zip_items modules __go_modules_summaries '  ' modules
     ;;
@@ -156,7 +156,7 @@ _@go.modules_produce_listing() {
     # Should only happen if _@go.modules is updated and this case statement
     # isn't.
     @go.printf 'ERROR: Unknown action: %s\n' "$action" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   esac
   __go_modules_listing=("${modules[@]}")
 }
@@ -241,22 +241,24 @@ _@go.modules_list() {
     if [[ "$__go_module_name" == '*' ]]; then
       if [[ "${#module_specs[@]}" -ne 1 ]]; then
         @go.printf "Do not specify other patterns when '*' is present.\n" >&2
-        return 1
+        return "$_GO_EC_USAGE"
       fi
       _@go.modules_search
     elif [[ "$__go_module_name" =~ \*|/$ ]]; then
       _@go.modules_search "$__go_module_name"
     elif ! _@go.find_module; then
       @go.printf "Unknown module: $__go_module_name\n" >&2
-      return 1
+      return "$_GO_EC_NOTFND"
     else
       __go_modules+=("$__go_module_file")
     fi
   done
 
   local __go_modules_listing=()
-  if ! _@go.modules_produce_listing "$action"; then
-    return 1
+
+  _@go.modules_produce_listing "$action" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   fi
   printf '%s\n' "${__go_modules_listing[@]}"
 }
@@ -310,9 +312,9 @@ _@go.modules_tab_completion() {
 
   if [[ ( "$word_index" -ne '0' && "${first:0:1}" == '-' ) &&
         ( ! "$first" =~ $flags_pattern || "$first" == '--imported' ) ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   elif [[ "$first" =~ ^(-h|-help|--help)$ && "$word_index" -gt '1' ]]; then
-    return 1
+    return "$_GO_EC_SIGN1"
   fi
 
   if [[ "$#" -eq '0' || "$word_index" -eq '0' ]]; then
@@ -343,9 +345,11 @@ _@go.modules_tab_completion() {
   fi
 
   local __go_modules_listing=()
-  if ! _@go.modules_produce_listing; then
+
+  _@go.modules_produce_listing && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
     # Shouldn't happen, since modules_produce_listing isn't parsing summaries.
-    return 1
+    return "$ec"
   fi
   completions+=("${__go_modules_listing[@]}")
   @go.complete_remove_completions_already_present \
@@ -356,7 +360,7 @@ _@go.modules_tab_completion() {
 _@go.modules_list_imported() {
   if [[ "$#" -ne 0 ]]; then
     @go.printf 'The --imported option takes no other arguments.\n' >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   # Collect imported module info before _GO_USE_MODULES imports possibly more.
@@ -399,7 +403,7 @@ _@go.modules() {
     ;;
   -*)
     @go.printf "Unknown option: $action\n" >&2
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   *)
     # Here we treat $action as a potential glob pattern.
diff --git a/libexec/new b/libexec/new
index 276f750..88d519d 100755
--- a/libexec/new
+++ b/libexec/new
@@ -48,7 +48,7 @@ _@go.new_tab_completions() {
 
   if [[ "$word_index" -eq '0' ]]; then
     printf -- '--command --internal --public --test --type'
-    return
+    return "$_GO_EC_OK"
   fi
   ((--word_index))
 
@@ -64,27 +64,27 @@ _@go.new_tab_completions() {
     ;;
   --internal)
     if [[ "$word_index" -ne '0' ]] || ! cd "$_GO_SCRIPTS_DIR/lib"; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
     ;;
   --public)
     if [[ "$word_index" -ne '0' ]] || ! cd "$_GO_ROOTDIR/lib"; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
     ;;
   --test)
     if [[ "$word_index" -ne '0' ]] || ! cd "$_GO_ROOTDIR/$_GO_TEST_DIR"; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
     ;;
   --type)
     if [[ "$word_index" -ne '1' ]]; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
     shift
     ;;
   *)
-    return 1
+    return "$_GO_EC_USAGE"
     ;;
   esac
   @go.compgen -f -- "$1"
@@ -114,25 +114,25 @@ _@go.new_file() {
 
   if [[ -z "$file_path" ]]; then
     @go.printf 'No %sfile path specified.\n' "$file_type" >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   elif [[ ! "$permissions" =~ $permissions_pattern ]]; then
     @go.printf 'Invalid permissions specification "%s" for %sfile: %s\n' \
       "$permissions" "$file_type" "$relpath" >&2
-      return 1
+      return "$_GO_EC_ARGERR"
   elif [[ ! -d "$parent_dir" ]] && ! mkdir -p "$parent_dir"; then
     @go.printf "Couldn't create parent directory for new %sfile: %s\n" \
       "$file_type" "$relpath" >&2
-    return 1
+    return "$_GO_EC_CANTCREAT"
   elif [[ -f "$file_path" ]]; then
     @go.printf '%sfile already exists: %s\n' "$file_type" "$relpath" >&2
-    return 1
+    return "$_GO_EC_GENERR"
   elif ! printf -- '%s\n' "$@" >"$file_path"; then
     @go.printf 'Failed to create new %sfile: %s\n' "$file_type" "$relpath" >&2
-    return 1
+    return "$_GO_EC_CANTCREAT"
   elif ! chmod "$permissions" "$file_path"; then
     @go.printf 'Failed to set permissions for new %sfile to "%s": %s\n' \
       "$file_type" "$permissions" "$relpath" >&2
-    return 1
+    return "$_GO_EC_NOPERM"
   fi
 }
 
@@ -168,7 +168,7 @@ _@go.new_command_scripts() {
 
   if [[ "$#" -eq '0' ]]; then
     printf 'No command script name specified.\n' >&2
-    return 1
+    return "$_GO_EC_ARGERR"
   fi
 
   for cmd in "$@"; do
@@ -182,8 +182,9 @@ _@go.new_command_scripts() {
     fi
     new_scripts+=("$cmd_path")
 
-    if ! _@go.new_command_script "$cmd" "$cmd_path" "$is_last_cmd"; then
-      return 1
+    _@go.new_command_script "$cmd" "$cmd_path" "$is_last_cmd" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]] ; then
+      return "$ec"
     fi
   done
 
@@ -213,8 +214,9 @@ _@go.new_module() {
     ;;
   esac
 
-  if ! _@go.new_file "$module_type" "$module_path" '644' "${impl[@]}"; then
-    return 1
+  _@go.new_file "$module_type" "$module_path" '644' "${impl[@]}" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   elif command -v "$EDITOR" >/dev/null; then
     "$EDITOR" "$module_path"
   fi
@@ -248,8 +250,9 @@ _@go.new_test() {
     '@test "$SUITE: short description of your first test case" {'
     '}')
 
-  if ! _@go.new_file "Bats test" "$test_path" '644' "${impl[@]}"; then
-    return 1
+  _@go.new_file "Bats test" "$test_path" '644' "${impl[@]}" && ec=0 || ec="$?"
+  if [[ "$ec" -ne 0 ]] ; then
+    return "$ec"
   elif command -v "$EDITOR" >/dev/null; then
     "$EDITOR" "$test_path"
   fi
@@ -260,7 +263,7 @@ _@go.new() {
 
   if [[ "$#" -eq '0' ]]; then
     @go 'help' "${_GO_CMD_NAME[@]}" >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
   shift
 
@@ -283,8 +286,9 @@ _@go.new() {
     _@go.new_test "$_GO_ROOTDIR/$_GO_TEST_DIR/$1"
     ;;
   --type)
-    if ! _@go.new_file "$1" "$2" "${@:3}"; then
-      return 1
+    _@go.new_file "$1" "$2" "${@:3}" && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]]; then
+      return "$ec"
     elif [[ "$#" -le '3' ]] && command -v "$EDITOR" >/dev/null; then
       "$EDITOR" "$2"
     fi
@@ -292,7 +296,7 @@ _@go.new() {
   *)
     printf 'The first argument is "%s", but must be one of:\n  %s\n' \
       "$mode" '--command --internal --public --test --type' >&2
-    return 1
+    return "$_GO_EC_USAGE"
   esac
 }
 
diff --git a/libexec/path b/libexec/path
index 0921ec2..5ba962c 100755
--- a/libexec/path
+++ b/libexec/path
@@ -21,17 +21,18 @@ _@go.path() {
   if [[ "$#" -ne '0' ]]; then
     if _@go.source_builtin 'aliases' --exists "$1"; then
       echo '[alias]'
-      return
+      return "$_GO_EC_OK"
     elif _@go.source_builtin 'builtins' --exists "$1"; then
       echo -n '[builtin] '
     fi
 
     local __go_cmd_path
 
-    if _@go.set_command_path_and_argv "$@"; then
+    _@go.set_command_path_and_argv "$@" && ec=0 || ec="$?"
+    if [[ "$ec" -eq 0 ]]; then
       echo "${__go_cmd_path#$_GO_ROOTDIR/}"
     else
-      return 1
+      return "$ec"
     fi
   fi
 }
diff --git a/libexec/plugins b/libexec/plugins
index fe09450..d805c3a 100755
--- a/libexec/plugins
+++ b/libexec/plugins
@@ -55,7 +55,7 @@ _@go.plugins() {
     # Tab completions
     _@go.source_builtin 'commands' "$@" "$__go_plugins_pathspec"
   else
-    return 1
+    return "$_GO_EC_NOTFND"
   fi
 }
 
diff --git a/scripts/changes b/scripts/changes
index f08d04e..cb149ff 100755
--- a/scripts/changes
+++ b/scripts/changes
@@ -17,10 +17,13 @@ _changes() {
     # Tab completions
     local word_index="$2"
     if [[ "$word_index" -gt 1 ]]; then
-      return 1
+      return "$_GO_EC_GENERR"
     fi
-    git tag
-    return
+    git tag && ec=0 || ec="$?"
+    if [[ "$ec" -ne 0 ]]; then
+      return "$ec"
+    fi
+    return "$_GO_EC_OK"
   fi
 
   local start_ref="$1"
@@ -28,10 +31,10 @@ _changes() {
 
   if [[ -z "$start_ref" ]]; then
     echo "Start ref not specified." >&2
-    return 1
+    return "$_GO_EC_USAGE"
   elif [[ -z "$end_ref" ]]; then
     echo "End ref not specified." >&2
-    return 1
+    return "$_GO_EC_USAGE"
   fi
 
   git log '--pretty=format:%h %an <%ae>%n        %s%n' \
diff --git a/tests/vars.bats b/tests/vars.bats
index 9eedb0c..3bb3064 100644
--- a/tests/vars.bats
+++ b/tests/vars.bats
@@ -44,6 +44,25 @@ quotify_expected() {
     "declare -rx _GO_CORE_URL=\"$_GO_CORE_URL\""
     "declare -rx _GO_CORE_VERSION=\"$_GO_CORE_VERSION\""
     "declare -x _GO_COVERALLS_URL=\"$_GO_COVERALLS_URL\""
+    'declare -irx _GO_EC_ARGERR="71"'
+    'declare -irx _GO_EC_BADFRMT="69"'
+    'declare -irx _GO_EC_BASE="64"'
+    'declare -irx _GO_EC_CANTCREAT="73"'
+    'declare -irx _GO_EC_CONFIG="78"'
+    'declare -irx _GO_EC_DEPMISS="72"'
+    'declare -irx _GO_EC_EXT1="65"'
+    'declare -irx _GO_EC_EXT2="66"'
+    'declare -irx _GO_EC_GENERR="64"'
+    'declare -irx _GO_EC_IOERR="74"'
+    'declare -irx _GO_EC_MAX="78"'
+    'declare -irx _GO_EC_NOINPUT="68"'
+    'declare -irx _GO_EC_NOPERM="77"'
+    'declare -irx _GO_EC_NOTFND="70"'
+    'declare -irx _GO_EC_OFFSET="0"'
+    'declare -irx _GO_EC_OK="0"'
+    'declare -irx _GO_EC_SIGN1="75"'
+    'declare -irx _GO_EC_SIGN2="76"'
+    'declare -irx _GO_EC_USAGE="67"'
     'declare -a _GO_IMPORTED_MODULES=()'
     'declare -a _GO_IMPORTED_MODULE_CALLERS=()'
     'declare -a _GO_IMPORTED_MODULE_FILES=()'
@@ -118,6 +137,25 @@ quotify_expected() {
     "declare -rx _GO_CORE_URL=\"$_GO_CORE_URL\""
     "declare -rx _GO_CORE_VERSION=\"$_GO_CORE_VERSION\""
     "declare -x _GO_COVERALLS_URL=\"$_GO_COVERALLS_URL\""
+    "declare -irx _GO_EC_ARGERR=\"71\""
+    "declare -irx _GO_EC_BADFRMT=\"69\""
+    "declare -irx _GO_EC_BASE=\"64\""
+    "declare -irx _GO_EC_CANTCREAT=\"73\""
+    "declare -irx _GO_EC_CONFIG=\"78\""
+    "declare -irx _GO_EC_DEPMISS=\"72\""
+    "declare -irx _GO_EC_EXT1=\"65\""
+    "declare -irx _GO_EC_EXT2=\"66\""
+    "declare -irx _GO_EC_GENERR=\"64\""
+    "declare -irx _GO_EC_IOERR=\"74\""
+    "declare -irx _GO_EC_MAX=\"78\""
+    "declare -irx _GO_EC_NOINPUT=\"68\""
+    "declare -irx _GO_EC_NOPERM=\"77\""
+    "declare -irx _GO_EC_NOTFND=\"70\""
+    "declare -irx _GO_EC_OFFSET=\"0\""
+    "declare -irx _GO_EC_OK=\"0\""
+    "declare -irx _GO_EC_SIGN1=\"75\""
+    "declare -irx _GO_EC_SIGN2=\"76\""
+    "declare -irx _GO_EC_USAGE=\"67\""
     "declare -a _GO_IMPORTED_MODULES=(${expected_modules[*]})"
     "declare -a _GO_IMPORTED_MODULE_CALLERS=(${expected_module_callers[*]})"
     "declare -a _GO_IMPORTED_MODULE_FILES=(${expected_module_files[*]})"
@@ -168,6 +206,25 @@ quotify_expected() {
     "_GO_CORE_URL: $_GO_CORE_URL" \
     "_GO_CORE_VERSION: $_GO_CORE_VERSION" \
     "_GO_COVERALLS_URL: $_GO_COVERALLS_URL" \
+    "_GO_EC_ARGERR: $_GO_EC_ARGERR" \
+    "_GO_EC_BADFRMT: $_GO_EC_BADFRMT" \
+    "_GO_EC_BASE: $_GO_EC_BASE" \
+    "_GO_EC_CANTCREAT: $_GO_EC_CANTCREAT" \
+    "_GO_EC_CONFIG: $_GO_EC_CONFIG" \
+    "_GO_EC_DEPMISS: $_GO_EC_DEPMISS" \
+    "_GO_EC_EXT1: $_GO_EC_EXT1" \
+    "_GO_EC_EXT2: $_GO_EC_EXT2" \
+    "_GO_EC_GENERR: $_GO_EC_GENERR" \
+    "_GO_EC_IOERR: $_GO_EC_IOERR" \
+    "_GO_EC_MAX: $_GO_EC_MAX" \
+    "_GO_EC_NOINPUT: $_GO_EC_NOINPUT" \
+    "_GO_EC_NOPERM: $_GO_EC_NOPERM" \
+    "_GO_EC_NOTFND: $_GO_EC_NOTFND" \
+    "_GO_EC_OFFSET: $_GO_EC_OK" \
+    "_GO_EC_OK: $_GO_EC_OK" \
+    "_GO_EC_SIGN1: $_GO_EC_SIGN1" \
+    "_GO_EC_SIGN2: $_GO_EC_SIGN2" \
+    "_GO_EC_USAGE: $_GO_EC_USAGE" \
     "_GO_KCOV_DIR: $_GO_KCOV_DIR" \
     "_GO_ROOTDIR: $TEST_GO_ROOTDIR" \
     "_GO_SCRIPT: $TEST_GO_SCRIPT" \