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Consider the 2 bash commands below:

$ VAR="hello world"
$ ./script.sh "$VAR"

Line 1 stores the string hello world (quotes removed) to parameter VAR. Line 2 should be processed as follows:

  • 2 tokens result from tokenization stage (token 1 is .\script.sh and token 2 is "$VAR")
  • Parameter and variable expansion applies to token 2 ("$VAR" gives "hello world")
  • Word splitting does not apply to "hello world" due to the double quotes ("hello world" remains one word)
  • Quote removal occurs and removes the double quotes around "hello world" Upon execution, we should have hello world being passed as a single argument to ./script.sh.

Hence, there should be one unique positional parameter $1 which is being assigned the unique word hello world.

QUESTIONS

  • Precisely, at what stage of command evaluation order does $1 get assigned its value?
  • In case this happens after quote removal, what mechanism helps the shell keep track of what constitutes an argument?
  • Does the shell store an indexed representation of the final list of words (post-expansion)?
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The shell that runs ./script.sh "$VAR" will ultimately build the ARGV array of null terminated values for the command line which then gets passed to execv(). This array is built after all substitution, processing, and quote removal is complete.

The shell that runs from that will receive hello world as ARGV[1] which corresponds to $1.

Note that neither shell "assigns" $1 specifically in this case. It is passed in as an array and $1 references that array.

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  • So, is this the final list of words (excluding $0, which should be passed to ARGV[0]) that are passed to the ARGV[] array on a per-index basis? Commented Feb 9 at 22:59
  • Actually, I think ARGV[0] becomes $0. Not sure what you mean by "per index basis", the whole array is passed and the $N syntax references it. Commented Feb 9 at 23:07
  • 2
    Start your educational journey with man execve and its "See also"s. Commented Feb 10 at 0:55
  • Along with the positional parameters like $1 don't forget the special parameters $@, $*, and $#. There may be equivalents among the shell variables with names that start with BASH_. Commented Feb 10 at 7:10

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