bin/: Use explicit "--" separator for assert-arg usages

In order to prevent legitimate cases to fail as errors, such as:

  NUM='-10'
  eval "$(assert-arg "$NUM" '-n NUM')"

To prevent assert-arg(1) from treating "-10" as the options "-1 and -0,
they need to be put after the "--" separator.

This way, all usages of assert-arg(1) that had its first argument as a
variable were adapted, and the usage and examples of assert-arg itself
were updated to encourage this best practice.

1 files changed, 2 insertions, 2 deletions

diff --git a/bin/assert-arg b/bin/assert-arg
index d7bc8f4..3c8990a 100755
--- a/bin/assert-arg
+++ b/bin/assert-arg
@@ -4,7 +4,7 @@ set -eu
 usage() {
 	cat <<-'EOF'
 		Usage:
-		  assert-arg STRING MESSAGE
+		  assert-arg -- STRING MESSAGE
 		  assert-arg -h
 	EOF
 }
@@ -23,7 +23,7 @@ help() {
 
 		  Assert that $1 contains an argument, named FILENAME:
 
-		    $ eval "$(assert-arg "${1:-}" 'FILENAME')"
+		    $ eval "$(assert-arg -- "${1:-}" 'FILENAME')"
 	EOF
 }