On Fri, Oct 4, 2019 at 9:08 AM Cameron Simpson <c...@cskk.id.au> wrote: > > On 03Oct2019 23:55, Chris Angelico <ros...@gmail.com> wrote: > >On Thu, Oct 3, 2019 at 11:41 PM Hongyi Zhao <hongyi.z...@gmail.com> wrote: > >> I'm very confusing on the following part in this script: > >> > >> ---- > >> ''':' # begin python string; this line is interpreted by the shell as `:` > >> which python >/dev/null 2>&1 && exec python "$0" "$@" > >> which python3 >/dev/null 2>&1 && exec python3 "$0" "$@" > >> which python2 >/dev/null 2>&1 && exec python2 "$0" "$@" > >> >&2 echo "error: cannot find python" > >> exit 1 > >> ''' > >> ---- > >> > >> Any hints for the meaning of several ' used above? > > > >The hint is there in that line, and stems from the way two different > >parsers (Python and sh) interpret the line. [...] > > > >In the shell, the first two are an > >empty string, then ':' is a colon, which introduces a label (the fact > >that it's in quotes is irrelevant to the shell). So there's an empty > >label followed by a shell comment. > > No. ":" is a synonym for "true". (Like "[" is a synonym for "test".) > > There aren't labels in the shell. This is just a dummy "true" command, > with a comment.
My bad. I remember using a leading colon-space as a multi-shell comment, and in at least some of them, it's a label (probably old MS-DOS batch files or something, given what my background is). In any case, that one line does nothing, but the subsequent lines are meaningful. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
