zsh-users
 help / color / mirror / Atom feed
* if (()){}else{} documented?
@ 2021-04-20 14:40 david
  2021-04-20 15:19 ` Marc Chantreux
  2021-04-20 15:33 ` Lawrence Velázquez
  0 siblings, 2 replies; 12+ messages in thread
From: david @ 2021-04-20 14:40 UTC (permalink / raw)
  To: zsh-users

Hi

I have been in a world of pain playing around with compound control 
structures

e.g. this only works as a single line (is that true?)

  if (( $1 == 4 )) { echo good } else { echo bad }

just wondered where I could read up on this?



f(){if (($1==4)){echo ok} else {echo nok} }

or

joe(){ [[ $1 > 4 ]] && echo big || echo small }

or

fred(){ if [[ $1  =~ fred ]] { echo ok} else {echo nok} }


There seems to be some arbitrariness as to when spaces are required

zzapper



^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 14:40 if (()){}else{} documented? david
@ 2021-04-20 15:19 ` Marc Chantreux
  2021-04-20 15:28   ` Lawrence Velázquez
  2021-04-21  8:46   ` zzapper
  2021-04-20 15:33 ` Lawrence Velázquez
  1 sibling, 2 replies; 12+ messages in thread
From: Marc Chantreux @ 2021-04-20 15:19 UTC (permalink / raw)
  To: david; +Cc: zsh-users

Hi David,

> e.g. this only works as a single line (is that true?)
> if (( $1 == 4 )) { echo good } else { echo bad }

i'm not sure what a "single line" is. the "else" keyword should
not appear at the very begin of an expression but all the rest is ok.

meaning those are correct

     if (( $1 == 4 )) { echo good } else { echo bad }

     if (( $1 == 4 )) {
         echo good
     } else {
         echo bad
     }

this is not

     if (( $1 == 4 )) {
         echo good
     }
     else {
         echo bad
     }

> just wondered where I could read up on this?

all the following examples works fine there. i'm even surprised about
this one

> joe(){ [[ $1 > 4 ]] && echo big || echo small }

this is a math expression so i would have written

joe(){ (( $1 > 4 )) && echo big || echo small }

regards
marc


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 15:19 ` Marc Chantreux
@ 2021-04-20 15:28   ` Lawrence Velázquez
  2021-04-20 15:32     ` Marc Chantreux
  2021-04-21  8:46   ` zzapper
  1 sibling, 1 reply; 12+ messages in thread
From: Lawrence Velázquez @ 2021-04-20 15:28 UTC (permalink / raw)
  To: Marc Chantreux, david; +Cc: zsh-users

On Tue, Apr 20, 2021, at 11:19 AM, Marc Chantreux wrote:
> all the following examples works fine there. i'm even surprised about
> this one
> 
> > joe(){ [[ $1 > 4 ]] && echo big || echo small }
> 
> this is a math expression so i would have written
> 
> joe(){ (( $1 > 4 )) && echo big || echo small }

You'd be right because the original version is wrong (unless OP
*wants* lexicographic comparison and just didn't say so).

	% joe(){ [[ $1 > 4 ]] && echo big || echo small }
	% joe 5
	big
	% joe 10
	small

-- 
vq


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 15:28   ` Lawrence Velázquez
@ 2021-04-20 15:32     ` Marc Chantreux
  0 siblings, 0 replies; 12+ messages in thread
From: Marc Chantreux @ 2021-04-20 15:32 UTC (permalink / raw)
  To: Lawrence Velázquez; +Cc: david, zsh-users

> You'd be right because the original version is wrong (unless OP
> *wants* lexicographic comparison and just didn't say so).
> 	% joe(){ [[ $1 > 4 ]] && echo big || echo small }

ohh ... indeed :)

thanks
marc


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 14:40 if (()){}else{} documented? david
  2021-04-20 15:19 ` Marc Chantreux
@ 2021-04-20 15:33 ` Lawrence Velázquez
  2021-04-21  9:16   ` zzapper
  1 sibling, 1 reply; 12+ messages in thread
From: Lawrence Velázquez @ 2021-04-20 15:33 UTC (permalink / raw)
  To: david; +Cc: zsh-users

On Tue, Apr 20, 2021, at 10:40 AM, david wrote:
> Hi
> 
> I have been in a world of pain playing around with compound control 
> structures
> 
> e.g. this only works as a single line (is that true?)
> 
>   if (( $1 == 4 )) { echo good } else { echo bad }
> 
> just wondered where I could read up on this?

The zshmisc(1) man page, section "ALTERNATE FORMS FOR COMPLEX
COMMANDS".  It assumes familiarity with lists, so probably also
look at "SIMPLE COMMANDS & PIPELINES".

-- 
vq


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 15:19 ` Marc Chantreux
  2021-04-20 15:28   ` Lawrence Velázquez
@ 2021-04-21  8:46   ` zzapper
  2021-04-21 10:41     ` Marc Chantreux
  2021-04-21 13:57     ` Bart Schaefer
  1 sibling, 2 replies; 12+ messages in thread
From: zzapper @ 2021-04-21  8:46 UTC (permalink / raw)
  To: Marc Chantreux, zsh-users


On 20/04/2021 16:19, Marc Chantreux wrote:
>
> not appear at the very begin of an expression but all the rest is ok.
>
> meaning those are correct
>
>       if (( $1 == 4 )) { echo good } else { echo bad }
>
>       if (( $1 == 4 )) {
>           echo good
>       } else {
>           echo bad
>       }
>
> this is not
>
>       if (( $1 == 4 )) {
>           echo good
>       }
>       else {
>           echo bad
>       }

This is very helpful & clarifies. I 'd forgotten that shells are more 
strict in their response to 'white space' than programming languages .

While playing golf I've noticed that the  'else' clause is particularly 
intolerant it needs '} else {'



^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-20 15:33 ` Lawrence Velázquez
@ 2021-04-21  9:16   ` zzapper
  0 siblings, 0 replies; 12+ messages in thread
From: zzapper @ 2021-04-21  9:16 UTC (permalink / raw)
  To: zsh-users

[-- Attachment #1: Type: text/plain, Size: 1939 bytes --]


On 20/04/2021 16:33, Lawrence Velázquez wrote:
> SIMPLE COMMANDS & PIPELINES

A /sublist/ is either a single pipeline, or a sequence of two or more 
pipelines separated by ‘&&’ or ‘||’. If two pipelines are separated by 
‘&&’, the second pipeline is executed only if the first succeeds 
(returns a zero status). If two pipelines are separated by ‘||’, the 
second is executed only if the first fails (returns a nonzero status). 
Both operators have equal precedence and are left associative. The value 
of the sublist is the value of the last pipeline executed. For example,

dmesg | grep panic && print yes

is a sublist consisting of two pipelines, the second just a simple 
command which will be executed if and only if the grep command returns a 
zero status. If it does not, the value of the sublist is that return 
status, else it is the status returned by the print (almost certainly 
zero).

A /list/ is a sequence of zero or more sublists, in which each sublist 
is terminated by ‘;’, ‘&’, ‘&|’, ‘&!’, or a newline. This terminator may 
optionally be omitted from the last sublist in the list when the list 
appears as a complex command inside ‘(...)’ or ‘{...}’. When a sublist 
is terminated by ‘;’ or newline, the shell waits for it to finish before 
executing the next sublist. If a sublist is terminated by a ‘&’, ‘&|’, 
or ‘&!’, the shell executes the last pipeline in it in the background, 
and does not wait for it to finish (note the difference from other 
shells which execute the whole sublist in the background). A 
backgrounded pipeline returns a status of zero.

More generally, a list can be seen as a set of any shell commands 
whatsoever, including the complex commands below; this is implied 
wherever the word ‘list’ appears in later descriptions. For example, the 
commands in a shell function form a special sort of list.


lv thanks will digest


[-- Attachment #2: Type: text/html, Size: 2929 bytes --]

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-21  8:46   ` zzapper
@ 2021-04-21 10:41     ` Marc Chantreux
  2021-04-21 12:32       ` zzapper
  2021-04-21 13:57     ` Bart Schaefer
  1 sibling, 1 reply; 12+ messages in thread
From: Marc Chantreux @ 2021-04-21 10:41 UTC (permalink / raw)
  To: zzapper; +Cc: zsh-users

> While playing golf I've noticed that the 'else' clause is particularly
> intolerant it needs '} else {'

'else' is not the problem: expressions are :) (problem of priority?)

this is ok

    if {true} {echo ok} else {echo nope}

those are syntax errors

    if{true} {echo ok} else {echo nope}
    if {true}{echo ok} else {echo nope}
    if {true} {echo ok} else{echo nope}

this does not echoes what you expected :)

    if {true} {echo ok}else {echo nope}

regards
marc




^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-21 10:41     ` Marc Chantreux
@ 2021-04-21 12:32       ` zzapper
  2021-04-21 14:59         ` Marc Chantreux
  2021-04-21 15:01         ` Marc Chantreux
  0 siblings, 2 replies; 12+ messages in thread
From: zzapper @ 2021-04-21 12:32 UTC (permalink / raw)
  To: zsh-users


On 21/04/2021 11:41, Marc Chantreux wrote:
> this does not echoes what you expected:)
>
>      if {true} {echo ok}else {echo nope}
I'd come across this when I was tying myself up in knots it's quite 
logical really when you think about it LOL


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-21  8:46   ` zzapper
  2021-04-21 10:41     ` Marc Chantreux
@ 2021-04-21 13:57     ` Bart Schaefer
  1 sibling, 0 replies; 12+ messages in thread
From: Bart Schaefer @ 2021-04-21 13:57 UTC (permalink / raw)
  To: zzapper; +Cc: Zsh Users

On Wed, Apr 21, 2021 at 1:46 AM zzapper <zsh@rayninfo.co.uk> wrote:
>
> While playing golf I've noticed that the  'else' clause is particularly
> intolerant it needs '} else {'

Actually it only needs "} else", the next statement can appear on a
new line.  In fact the next statement doesn't even have to be enclosed
in braces.

I believe the only case where all three must be on the same line is
  } always {


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-21 12:32       ` zzapper
@ 2021-04-21 14:59         ` Marc Chantreux
  2021-04-21 15:01         ` Marc Chantreux
  1 sibling, 0 replies; 12+ messages in thread
From: Marc Chantreux @ 2021-04-21 14:59 UTC (permalink / raw)
  To: zzapper; +Cc: zsh-users

Le Wed, Apr 21, 2021 at 01:32:00PM +0100, zzapper a écrit :
> On 21/04/2021 11:41, Marc Chantreux wrote:
> > this does not echoes what you expected:)
> >      if {true} {echo ok}else {echo nope}
> I'd come across this when I was tying myself up in knots it's quite logical
> really when you think about it LOL

i don't think so :) i guess this behavior isn't intentional at the
begining but stay there because of retrocompatibility.

regards



^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: if (()){}else{} documented?
  2021-04-21 12:32       ` zzapper
  2021-04-21 14:59         ` Marc Chantreux
@ 2021-04-21 15:01         ` Marc Chantreux
  1 sibling, 0 replies; 12+ messages in thread
From: Marc Chantreux @ 2021-04-21 15:01 UTC (permalink / raw)
  To: zzapper; +Cc: zsh-users

Le Wed, Apr 21, 2021 at 01:32:00PM +0100, zzapper a écrit :
> 
> On 21/04/2021 11:41, Marc Chantreux wrote:
> > this does not echoes what you expected:)
> >      if {true} {echo ok}else {echo nope}
> I'd come across this when I was tying myself up in knots it's quite logical
> really when you think about it LOL

i don't think so. i guess it is unintentional but kept that way for
compatibility reasons?

regards
marc


^ permalink raw reply	[flat|nested] 12+ messages in thread

end of thread, other threads:[~2021-04-21 16:00 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-20 14:40 if (()){}else{} documented? david
2021-04-20 15:19 ` Marc Chantreux
2021-04-20 15:28   ` Lawrence Velázquez
2021-04-20 15:32     ` Marc Chantreux
2021-04-21  8:46   ` zzapper
2021-04-21 10:41     ` Marc Chantreux
2021-04-21 12:32       ` zzapper
2021-04-21 14:59         ` Marc Chantreux
2021-04-21 15:01         ` Marc Chantreux
2021-04-21 13:57     ` Bart Schaefer
2021-04-20 15:33 ` Lawrence Velázquez
2021-04-21  9:16   ` zzapper

zsh-users

This inbox may be cloned and mirrored by anyone:

	git clone --mirror http://inbox.vuxu.org/zsh-users

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V1 zsh-users zsh-users/ http://inbox.vuxu.org/zsh-users \
		zsh-users@zsh.org
	public-inbox-index zsh-users

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.vuxu.org/vuxu.archive.zsh.users


code repositories for the project(s) associated with this inbox:

	https://git.vuxu.org/mirror/zsh/

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git