Bash Arithmetic – Fixing Math Failures with Leading Zero in Bash Double Paren

Prefix the first number with a 0 to force each term to have the same width.

$ echo {08..10}
08 09 10

From the bash man page section on Brace Expansion:

Supplied integers may be prefixed with 0 to force each term to have the same width. When either x or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary.

Also note that you can use seq with the -w option to equalize width by padding with leading zeroes:

$ seq -w 8 10
08
09
10

$ seq -s " " -w 8 10
08 09 10

If you want more control, you can even specify a printf style format:

$ seq -s " " -f %02g 8 10
08 09 10

I'm torn between whether this is a poor implementation or poor documentation. Bash says this about quote removal:

Quote Removal

After the preceding expansions, all unquoted occurrences of the characters \, ', and " that did not result from one of the above expansions are removed.

I think the key might be "all unquoted occurrences" in that paragraph. Everything inside $(( )) is treated as if it's in double quotes, per the documentation. Those characters are all quoted if they're inside the parens, making quote removal essentially a noop. For example, note how the other "removed" chars are treated (also note how trailing space is preserved, due to how quoted strings are parsed):

$ echo $(( '5' ))
bash: '5' : syntax error: operand expected (error token is "'5' ")
$ echo $(( \ ))
bash: \ : syntax error: operand expected (error token is "\ ")

Skimming the source code, the quotes do need to be balanced, as a result of the code which scans to identify if $(( )) is math or a nested legacy subexpression. When the string is identified as an arithmetic expression, it's then parsed as if it's double quoted - which means all the chars inside are considered quoted before quote removal happens.

Personally, this is part of why I prefer ksh - especially for math. It treats the single-quoted 5 above as a C string which evaluates as 53, for example. man ascii to see why that makes sense. :)