Understanding Ambiguous Redirects and Word Splitting in Bash

Yeah, I agree! And just to add, the issue mainly revolves around how bash interprets commands. When you have unquoted `$a`, it can lead to unexpected behavior during command execution due to splitting spaces into separate arguments. A best practice here is to always wrap your variable expansions in quotes like: `"$a"`. This helps retain the original spacing without causing confusion in commands and redirections.

The "ambiguous redirect" you mentioned is often due to how bash processes commands. When the variable `$a` has whitespace, it can split the command line into multiple arguments, triggering that ambiguous error during redirection. To prevent this, always use double quotes around your variables when passing them as arguments! For instance: `ok "$a"` ensures the space is treated as intended.

You're on the right track, but keep in mind the distinctions between command substitution and parameter expansions. In your examples, once you expand a variable with whitespace like `$a`, it can lead to multiple outputs causing confusion for bash. Unquoted expansions allow whitespace to split arguments unless properly handled with quotes.

Great question! The "ambiguous redirection" error you're seeing is actually due to how bash handles word splitting and parameter expansion. When you use `$a`, which has spaces, bash will treat it as multiple arguments unless it's quoted. In your first example, `...$a"hhhhh"$....`, the presence of `$....` stops further expansions because `.` is not a valid variable, so it doesn't hit the split until everything is done.

In `ok$a"hhhhh"$USER`, after `$a` is expanded (resulting in spaces), bash tries to expand `$USER` next, and since there are now multiple words, it encounters the ambiguity. So the rule of thumb is to always quote variables when there's a chance of them containing spaces to avoid issues like these!