Re: why not promote the plague ? (brace|rc|alternative|modern) syntax

["Mark J. Reed" <markjreed@xxxxxxxxx>]

Sorry, please ignore, was an old draft I accidentally sent.

On Mon, Dec 16, 2024 at 4:05 PM Mark J. Reed <markjreed@xxxxxxxxx> wrote:

Let's try this again:

First, we have the standard syntax that works in any POSIX shell:

    for var in val1 val2 val3; do command1; command2; done

    while command1; command2; do command3; command4; done

    until command1; command2; do command3; command4; done

    if command1; command2; then command3; command4; else command5; command6; fi

The C-style for loop is not part of POSIX, but is common to bash, ksh, and zsh:

    for (( init; condition; increment )) do command1; command2; done

The repeat loop is purely a Zsh innovation not present in the other shells:

    repeat $times; do command1; command2; done 

 

All of the above have alternative syntax in Zsh that works irrespective of the SHORT_LOOPS option.

So far, so correct, but I got a little too specific with the details. 

Since all of these constructs have the form intro-keyword part1 keyword1 part2 keyword2, the basic idea is to replace keyword1 and keyword2 with curly braces.  But the for...in loop also has a keyword0, namely in, which needs its own d

    for var (val1 val2 val3) { command1; command2; }

    while (command1; command2) { command3; command4; }

    until (command1; command2) { command3; command4; }

    if (command1; command2) { command3; command4; } else { command5; command6; }

    for (( init; condition; increment )) { command1; command2; }

    repeat $times { command1; command2; }

NOTE: If the conditional command for while/until/if is a single ((...)) or [[...]] test, you don't need the extra parentheses around it.

Finally, we have the Zsh "short" syntax, which works only with setopt SHORT_LOOPS, and only if the body is a single command:

    for var (val1 val2 val3) command1; 

    while (command1; command2) command3

    until (command1; command2) command3

    if (command1; command2) command3;

    for (( init; condition; increment )) command1;

NOTE: again, the parentheses can be omitted around a single ((...)) or [[...]] test. Also, as far as I know, there's no way to attach an else to an if when using the short syntax. 

On Sat, Dec 14, 2024 at 2:29 AM Marc Chantreux <mc@xxxxxxxxxx> wrote:

On Fri, Dec 13, 2024 at 07:07:17PM -0500, Lawrence Velázquez wrote:
> Mikael's point was to distinguish between the alternative forms
> and the SHORT_LOOPS forms.  None of your examples works without
> SHORT_LOOPS

thanks for noticing. which leads me to open zshmisc(1) and read
read "ALTERNATE FORMS FOR COMPLEX COMMANDS". TIL that my coding
style is actually a mix of the alternative form and SHORT_LOOPS
and the difference is subtile:

        « The  short  versions  below only work if sublist is of the form `{
        list }' or if the SHORT_LOOPS option is set »

regards
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Marc Chantreux

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Mark J. Reed <markjreed@xxxxxxxxx>

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Mark J. Reed <markjreed@xxxxxxxxx>

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Mark J. Reed <markjreed@xxxxxxxxx>