I have one script - two versions; these are test scripts to solve my problem/issue.
The difference between the two scripts is that the "for....loop" in script 'loop1' uses a variable ($xlim) to control the loop; whereas in script 'loop2' the loop parameter are fixed integers.
Of course, my actual script needs a 'parametric loop' like in script 'loop1'.
So why if one of the loop parameters is not a 'static' (constant) value does "I = {1..5}" and not "I = 1", i.e why does $i substitute to "{1..5}"?
I have not been able to find any help otherwise and would appreciate any advice!
The observed behaviour can be understood by carefully reading the man page, e.g. man bash:
Quote:
EXPANSION
...
The order of expansions is: brace expansion; tilde expansion, parameter and variable expansion, ...
...
Brace Expansion
Brace expansion is a mechanism by which arbitrary strings may be generated.
...
A sequence expression takes the form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an optional increment, is an integer.
...
Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result.
...
A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid sequence expression. Any incorrectly formed brace expansion is left unchanged.
As laid out, brace expansion is the first to take place, and it needs x and y to integers or characters, NOT variable references, which in turn make it fail and leave the construct unchanged (resulting in one single element (literal "{1..$xlim}") in the for loop and leading to the error message that you see in your post).
Others have shown before that you could use (the highly deprecated because inherently dangerous) evalto get the desired results, or e.g. use the seq command for your for loop:
You can't do that in bash however if you really need to do something like {1..5} then this is a workaround. Not recommended though...
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