cleanup of help, info and error messages

nft-edit-ruleset

@@ -68,19 +68,39 @@ yes=false
 while true ; do
   case "$1" in
     -h|--help)
+      # shellcheck disable=SC2016
+      backticks='```'
       cat << EOF
-Usage: nft-edit-ruleset [--config [CONFIG_FILE]] [--fail] [--timeout SECONDS] [--yes] 
-Description:
- Interactively edit the current nftables ruleset using the editor specified
- by environment variable EDITOR (defaulting to vim). Optionally, revert
- changes after a timeout given in seconds.
-Options:
- - \`-c\`, \`--config [CONFIG_FILE]\`: On successfully applying the  
-  changes, save ruleset to \`CONFIG_FILE\` (default: $default_config_file).
- - \`-f\`, \`--fail\`: Exit unsuccessfully if changes fail to apply.
- - \`-h\`, \`--help\`: Display this message and exit.
- - \`-t NUM\`, \`--timeout NUM\`: Revert changes after NUM seconds.
- - \`-y\`, \`--yes\`: No confirmation before applying changes.
+# SYNOPSIS
+$backticks
+nft-edit-ruleset [--config [CONFIG_FILE]] [--fail] [--timeout SECONDS] [--yes] 
+$backticks
+
+# DESCRIPTION
+Interactively edit the current nftables ruleset using the editor specified by
+environment variable EDITOR (defaulting to vim). Optionally, revert changes
+after a timeout given in seconds.
+
+# OPTIONS
+- \`-c\`, \`--config [CONFIG_FILE]\`:  
+  On success, save ruleset to \`CONFIG_FILE\` (default: $default_config_file).
+- \`-f\`, \`--fail\`:  
+  Exit unsuccessfully if changes fail to apply.
+- \`-h\`, \`--help\`:  
+  Display this message and exit.
+- \`-t NUM\`, \`--timeout NUM\`:  
+  Revert changes after NUM seconds.
+- \`-y\`, \`--yes\`:  
+  No confirmation before applying changes.
+
+# EXIT CODES
+- 0: Success: No changes to apply or changes applied successfully.
+- 1: Error: Usage error or failed or aborted changes.
+
+# AUTHOR AND LICENSE
+Copyleft 2021 Tilman Kranz <tilt@linuxfoo.de>  
+This software is distributed on the terms and conditions of the  
+MIT License [https://opensource.org/licenses/MIT](https://opensource.org/licenses/MIT)
 EOF
       exit 0
       ;;
@@ -96,7 +116,7 @@ EOF
         timeout=true
         timeout_secs=$1
       else
-        echo "ERROR: Missing argument for option \`--timeout\`, aborted."
+        echo "ERROR: Missing argument for option \`--timeout\`, aborted." >&2
       exit 1
       fi
       ;;
@@ -107,7 +127,10 @@ EOF
         shift 1
         config_file=$1
       elif test -z "$default_config_file" ; then
-        echo "ERROR: Option \`--config\` was used without an argument, but no default location of a file \"nftables.conf\" could be found (use \`--config CONFIG_FILE\` to specify a location); aborted."
+        echo \
+          "ERROR: Option \`--config\` was used without an argument," \
+          "but no default location of a file \"nftables.conf\" could be found" \
+          "(use \`--config CONFIG_FILE\` to specify a location); aborted." >&2
         exit 1
       else
         config_file=$default_config_file
@@ -117,7 +140,7 @@ EOF
       :
       ;;
     *)
-      echo "ERROR: Unknown or unexpected argument \"$1\"; aborted."
+      echo "ERROR: Unknown or unexpected argument \"$1\"; aborted." >&2
       exit 1
       ;;
   esac
@@ -133,7 +156,7 @@ done
 # Main Program
 
 if ! test -t ; then
-  echo "ERROR: Not connected to a terminal; aborted."
+  echo "ERROR: Not connected to a terminal; aborted." >&2
   exit 1
 fi
 
@@ -161,7 +184,7 @@ while true ; do
       if store_config "$tmp" "$config_file" ; then
         echo "Stored unchanged ruleset to config_file=\"$config_file\"."
       else
-        echo "ERROR: Storing unchanged ruleset to config_file=\"$config_file\" failed."
+        echo "ERROR: Storing unchanged ruleset to config_file=\"$config_file\" failed." >&2
         exit 1
       fi
     fi
@@ -205,7 +228,7 @@ while true ; do
         if store_config "$tmp" "$config_file" ; then
           echo "Stored changed ruleset to config_file=\"$config_file\"."
         else
-          echo "ERROR: Storing changed ruleset to config_file=\"$config_file\" failed."
+          echo "ERROR: Storing changed ruleset to config_file=\"$config_file\" failed." >&2
           exit 1
         fi
       fi
@@ -218,4 +241,4 @@ done
 ##
 # Exit Codes
 # - 0: Success: No changes to apply or changes applied successfully.
-# - 1: Error: Usage error or failed or aborted changes.
+# - 1: Error: Usage error, failed or aborted changes or failureto store configfile.