Possible bug in zargs

Possible bug in zargs

[Dima Kogan]

I can't seem to get the -n option in zargs to work right. This looks like a bug
to me, but maybe I'm not using it correctly:

dima@shorty:/tmp$ ls -l
total 12
-rw-r--r-- 1 dima dima 1 Oct 27 15:29 1
-rw-r--r-- 1 dima dima 5 Oct 27 15:29 2
-rw-r--r-- 1 dima dima 5 Oct 27 15:29 3


dima@shorty:/tmp$ zargs -- * -- ls -l 
-rw-r--r-- 1 dima dima 1 Oct 27 15:29 1
-rw-r--r-- 1 dima dima 5 Oct 27 15:29 2
-rw-r--r-- 1 dima dima 5 Oct 27 15:29 3

dima@shorty:/tmp$ zargs -- * -- ls   
1  2  3

dima@shorty:/tmp$ zargs -n1 -- * -- ls 
1
2
3

dima@shorty:/tmp$ zargs -n1 -- * -- ls -l
zargs: argument list too long



The "argument list too long" doesn't make sense here.

Thanks

Re: Possible bug in zargs

[Dima Kogan]

[-- Attachment #1: Type: text/plain, Size: 962 bytes --]

> On Sat, 27 Oct 2012 15:34:00 -0700
> Dima Kogan <zsh@dima.secretsauce.net> wrote:
>
> I can't seem to get the -n option in zargs to work right. This looks like a bug
> to me, but maybe I'm not using it correctly:
> 
> dima@shorty:/tmp$ ls -l
> total 12
> -rw-r--r-- 1 dima dima 1 Oct 27 15:29 1
> -rw-r--r-- 1 dima dima 5 Oct 27 15:29 2
> -rw-r--r-- 1 dima dima 5 Oct 27 15:29 3
> 
> 
> dima@shorty:/tmp$ zargs -- * -- ls -l 
> -rw-r--r-- 1 dima dima 1 Oct 27 15:29 1
> -rw-r--r-- 1 dima dima 5 Oct 27 15:29 2
> -rw-r--r-- 1 dima dima 5 Oct 27 15:29 3
> 
> dima@shorty:/tmp$ zargs -- * -- ls   
> 1  2  3
> 
> dima@shorty:/tmp$ zargs -n1 -- * -- ls 
> 1
> 2
> 3
> 
> dima@shorty:/tmp$ zargs -n1 -- * -- ls -l
> zargs: argument list too long


Attached is a patch that fixes this. There was some misbehaving logic in the
script. I don't understand why that logic was ever necessary. Does anybody know
why the value of $n was connected to the value of $c at all?

[-- Attachment #2: 0001-n-option-of-zargs-now-works-correctly.patch --]
[-- Type: text/x-patch, Size: 994 bytes --]

>From b2d0722f78ce1c8effd69119b989a9112cbf5d27 Mon Sep 17 00:00:00 2001
From: Dima Kogan <dima@secretsauce.net>
Date: Tue, 30 Oct 2012 00:02:45 -0700
Subject: [PATCH] -n option of zargs now works correctly

Before this patch, the following wouls happen:

dima@shorty:/tmp$ ls
1  2  3

dima@shorty:/tmp$ zargs -n1 -- * -- ls -l
zargs: argument list too long
---
 Functions/Misc/zargs |    9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/Functions/Misc/zargs b/Functions/Misc/zargs
index 71fd428..59b369e 100644
--- a/Functions/Misc/zargs
+++ b/Functions/Misc/zargs
@@ -212,20 +212,13 @@ then
     fi
 fi
 
-n=${${n##-(n|-max-args(=|))}:-$[ARGC+c]}
+n=${${n##-(n|-max-args(=|))}:-$[ARGC]}
 if (( n <= 0 ))
 then
     print -u2 'zargs: value for max-args must be >= 1'
     return 1
 fi
 
-if (( n > c ))
-then (( n -= c ))
-else
-    print -u2 zargs: argument list too long
-    return 1
-fi
-
 s=${${s##-(s|-max-chars(=|))}:-20480}
 if (( s <= 0 ))
 then
-- 
1.7.10.4

Re: Possible bug in zargs

[Bart Schaefer]

On Oct 30, 12:05am, Dima Kogan wrote:
}
} Attached is a patch that fixes this. There was some misbehaving logic
} in the script. I don't understand why that logic was ever necessary.
} Does anybody know why the value of $n was connected to the value of $c
} at all?

Sorry, meant to reply to this thread earlier but I had an unusually busy
weekend.  Short answer:  The previous behavior was the intended behavior
and I'm going to recommend against accepting this patch.

$n represents the maximum number of arguments that may be passed to the
called command.  NOT the maximum number of arguments that may be taken
from the input list and added to the other arguments of the command, but
the maximum that may be passed to the command, period.

$c is the number of arguments of the command that appear outside of the
input list, that is, the number of arguments that trail the end of the
whole zargs construct.  In your example:

} > dima@shorty:/tmp$ zargs -n1 -- * -- ls -l
} > zargs: argument list too long

You've said that "ls" should be passed at most one argument (-n1).  That 
one argument is "-l".  Therefore there is no room to pass any of the
arguments from the input list (expansion of "*") without passing too
many arguments, so you get the error.

This may seem silly your example above, but it could be very important
if for example you're using a larger value of -n with some sort of
$(command) substitution generating the command for zargs to execute.

What you actually want in your example is this:

    zargs -l1 -- * -- ls -l

The manual page explains this:

     The options -i, -I, -l, -L, and -n differ slightly from their
     usage in xargs.  There are no input lines for zargs to count, so
     -l and -L count through the INPUT list, and -n counts the number
     of arguments passed to each execution of COMMAND, _including_ any
     ARG list.  Also, any time -i or -I is used, each INPUT is
     processed separately as if by `-L 1'.

Re: Possible bug in zargs

[Dima Kogan]

> On Tue, 30 Oct 2012 09:09:09 -0700
> Bart Schaefer <schaefer@brasslantern.com> wrote:
>
> On Oct 30, 12:05am, Dima Kogan wrote:
> }
> } Attached is a patch that fixes this. There was some misbehaving logic
> } in the script. I don't understand why that logic was ever necessary.
> } Does anybody know why the value of $n was connected to the value of $c
> } at all?
> 
> Sorry, meant to reply to this thread earlier but I had an unusually busy
> weekend.  Short answer:  The previous behavior was the intended behavior
> and I'm going to recommend against accepting this patch.
> 
> $n represents the maximum number of arguments that may be passed to the
> called command.  NOT the maximum number of arguments that may be taken
> from the input list and added to the other arguments of the command, but
> the maximum that may be passed to the command, period.
> 
> $c is the number of arguments of the command that appear outside of the
> input list, that is, the number of arguments that trail the end of the
> whole zargs construct.  In your example:
> 
> } > dima@shorty:/tmp$ zargs -n1 -- * -- ls -l
> } > zargs: argument list too long
> 
> You've said that "ls" should be passed at most one argument (-n1).  That 
> one argument is "-l".  Therefore there is no room to pass any of the
> arguments from the input list (expansion of "*") without passing too
> many arguments, so you get the error.
> 
> This may seem silly your example above, but it could be very important
> if for example you're using a larger value of -n with some sort of
> $(command) substitution generating the command for zargs to execute.
> 
> What you actually want in your example is this:
> 
>     zargs -l1 -- * -- ls -l
> 
> The manual page explains this:
> 
>      The options -i, -I, -l, -L, and -n differ slightly from their
>      usage in xargs.  There are no input lines for zargs to count, so
>      -l and -L count through the INPUT list, and -n counts the number
>      of arguments passed to each execution of COMMAND, _including_ any
>      ARG list.  Also, any time -i or -I is used, each INPUT is
>      processed separately as if by `-L 1'.
> 

Thanks, Bart. I indeed missed that part of the doc. Sorry for the false alarm.

dima