Re: [PATCH va/i18n-even-more] rebase-interactive: trim leading whitespace from progress count

On Thu, Jul 28, 2016 at 1:47 PM, Johannes Sixt [off-list ref] wrote:

Interactive rebase uses 'wc -l' to write the current patch number
in a progress report. Some implementations of 'wc -l' produce spaces
before the number, leading to ugly output such as

  Rebasing (     3/8)

Remove the spaces using a trivial arithmetic evaluation.

Before 9588c52 (i18n: rebase-interactive: mark strings for
translation) this was not a problem because printf was used to
generate the text. Since that commit, the count is interpolated
directly from a shell variable into the text, where the spaces
remain. The total number of patches does not have this problem
even though it is interpolated from a shell variable in the same
manner, because the variable is set by an arithmetic evaluation.

Later in the script, there is a virtually identical case where
leading spaces are trimmed, but it uses a pattern substitution:

todocount=$(git stripspace --strip-comments <"$todo" | wc -l)
todocount=${todocount##* }

I did not choose this idiom because it adds a line of code, and
there is already an arithmetic evaluation in the vicinity of the
line that is changed here.

On the other hand, to a newcomer (not familiar with this patch),
${foo##* } is an obvious and intentional stripping of whitespace,
whereas taking advantage of a side-effect of arithmetic evaluation to
achieve the same is quite subtle and likely to be interpreted as
pointless, thus forces the reader to consult 'blame' to understand why
the code is the way it is.