improve exit code use in bin scripts

The use of exit codes and exit code ranges has been
made more consistent across most bin tools.

bin/subst.default.sh

@@ -58,7 +58,7 @@ shopt -s globstar	# enable ** to match all files and zero or more directories an
 
 # set variables referenced in the usage message
 #
-export VERSION="1.2 2024-02-05"
+export VERSION="1.2.1 2024-02-23"
 NAME=$(basename "$0")
 export NAME
 export V_FLAG=0
@@ -66,7 +66,7 @@ GIT_TOOL=$(type -P git)
 export GIT_TOOL
 if [[ -z "$GIT_TOOL" ]]; then
     echo "$0: FATAL: git tool is not installed or not in \$PATH" 1>&2
-    exit 210
+    exit 5
 fi
 "$GIT_TOOL" rev-parse --is-inside-work-tree >/dev/null 2>&1
 status="$?"
@@ -107,12 +107,12 @@ export USAGE="usage: $0 [-h] [-v level] [-V] [-d topdir] [-D docroot/] [-n] [-N]
 
 Exit codes:
      0         all OK
-     1	       pandoc exited non-zero
+     1	       some internal tool exited non-zero
      2         -h and help string printed or -V and version string printed
      3         command line error
      4         bash version is < 4.2
- >= 10  < 210  ((not used))
- >= 210	       internal tool error
+     5	       some internal tool is not found or not an executable file
+ >= 10         internal error
 
 $NAME version: $VERSION"