Positional Parameters and shift

#!/bin/bash
set -- alpha beta gamma
echo "script/function name placeholder: $0"
echo "first: $1, second: $2, third: $3"
echo "total arguments: $#"

#!/bin/bash
set -- one two three
while [[ $# -gt 0 ]]; do
    echo "processing: $1"
    shift
done
echo "no arguments left: $#"

#!/bin/bash
set -- --name Ada extra1 extra2
if [[ $1 == "--name" ]]; then
    value=$2
    shift 2
fi
echo "parsed name: $value"
echo "remaining: $*"

#!/bin/bash
show_args() {
    echo "inside function: $1 $2"
}

set -- outer1 outer2
echo "outer script args: $1 $2"
show_args inner1 inner2
echo "outer script args unchanged: $1 $2"

1. Forgetting $0 is the script's own name, not the first argument; the first real argument is $1.
2. Using $* when "$@" was needed, losing the distinction between separate arguments once word splitting or quoting differs.
3. Calling shift more times than there are remaining arguments, which is usually harmless but can be a sign of a loop-counting bug.

• $0 is the script name, $1, $2, ... are the actual arguments, and $# is the argument count.
• shift (or shift N) discards the first (or first N) positional parameters, renumbering the rest.
• A while [[ $# -gt 0 ]]; do ...; shift; done loop is a standard way to process an unknown number of arguments one at a time.
• Inside a function, positional parameters refer to the function's own arguments, not the script's.