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To assign positional parameters, use set -- first second .. (or use [ ] to compare).

Problematic code:

if [ -z "$1" ]
then
  $1="help"
fi

or

if $1="help"
then
  echo "Usage: $0 filename"
fi

Correct code:

if [ -z "$1" ]
then
  set -- "help"
fi

or

if [ $1 = "help" ]
then
  echo "Usage: $0 filename"
fi

Rationale:

You have a command on the form $2=value.

If the goal is to assign a new value to the positional parameters, use the set builtin: set -- one two .. will cause $1 to be "one" and $2 to be "two".

If you instead want to compare the value, use [ ] and add spaces: [ "$1" = "foo" ]

Exceptions:

None

Related resources:

• Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!

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