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Paste with null delimiter

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  Paste with null delimiter julio.neves@gmail.com - 2015-11-03 08:29 -0800
    Re: Paste with null delimiter Eric Blake <eblake@redhat.com> - 2015-11-03 10:41 -0700
    Re: Paste with null delimiter Andreas Schwab <schwab@linux-m68k.org> - 2015-11-03 18:47 +0100
    Re: Paste with null delimiter Eric Blake <eblake@redhat.com> - 2015-11-03 13:32 -0700
    Re: Paste with null delimiter Eric Blake <eblake@redhat.com> - 2015-11-03 13:43 -0700
    Re: Paste with null delimiter Eric Blake <eblake@redhat.com> - 2015-11-03 13:52 -0700
    Re: Paste with null delimiter Andreas Schwab <schwab@linux-m68k.org> - 2015-11-03 22:57 +0100
    Re: Paste with null delimiter Stephane Chazelas <stephane.chazelas@gmail.com> - 2015-11-04 15:44 +0000

#11822 — Paste with null delimiter

An example is better than thousand words:

$ seq 1 2 9 > odd
$ seq 2 2 10 > even
$ paste -d "" odd even
12
34
56
78
910
$ paste -d"" odd even
2
4
6
8
10

Like you can see, with no space between the option (-d) and the null parameter (""), we have an unexpected result

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#11823

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On 11/03/2015 09:29 AM, julio.neves@gmail.com wrote:
> An example is better than thousand words:
> 
> $ seq 1 2 9 > odd
> $ seq 2 2 10 > even
> $ paste -d "" odd even
> 12
> 34
> 56
> 78
> 910
> $ paste -d"" odd even

This is equivalent to:

paste -dodd even

which is NOT the same as the NUL delimiter as the argument to -d.

There is no way to specify an empty string as the option to a short
option, except as a separate parameter.

This is not a bug in bash, but in your usage.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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#11824

julio.neves@gmail.com writes:

> $ paste -d"" odd even

This is the same as `paste -d odd even', so the delimiter list is odd.
As there is only one file, this in turn is the same as `paste even'.
Ultimately this is the same as `cat even'.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

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#11826

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On 11/03/2015 01:09 PM, Dennis Williamson wrote:
> On Nov 3, 2015 12:47 PM, "Julio C. Neves" <julio.neves@gmail.com> wrote:
>>
>> Thanks Dennis,
>> I know that you are rigth, but "paste -d"" odd even" and "paste -d "" odd
> even" are not the same? The diference is only a space between the option
> and its parameter.

They are indeed not the same.  In long option form, you have:

paste -d "" odd even
 ==
paste --delimiters="" odd even
 ==
paste --delimiters= odd even
 ==
paste --delimiters "" odd even

while:

paste -d"" odd even
 ==
paste -d odd even
 ==
paste --delimiters=odd even
 ==
paste --delimiters odd even

Remember, the shell strips quotes before it hands arguments to paste.
Thus, paste is receiving, as argv, ["paste", "-d", "", "odd", "even"]
for the first group, and ["paste", "-d", "odd", "even"] for the second
group.

There is NO way for any program using getopt() or getopt_long() to know
if the user spelled '-d""' vs. '"-d"' vs. '-d', or any other myriad of
patterns where the quotes are stripped.  The ONLY way to pass an empty
string argument to a short option is to do it as a separate argument,
because the quotes are already stripped by the time argv is formed.
Thus, the space is essential.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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#11827

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[adding the list back in with permission; please don't send private
mails when the discussion may benefit others]

[please don't top-post on technical lists]

On 11/03/2015 11:03 AM, Julio C. Neves wrote:
> Hi Eric, I wrote NUL because my english is not the best of the world, I
> wanna mean "empty" delimiter, I was not trying to use the binary zeroes as
> delimiter.
> 
> Using a space between the option and the delimiter it works fine, but if
> you take off this space, the first file disapears.
> 
> I can't agree that
> 
> paste -d odd even
> 
> is the same as:
> 
> paste -d odd even
> 

I think you typed that wrong, because what you typed is identical.

> In the 1st case we are specifying the delimiters as o, d and d again
> 
> let's use the -s option:
> 
> $ paste -sd odd even     # o, d & d are the delimiters
> 2o4d6d8o10
> $ paste -sd "" odd even  # An empty delimiter
> 13579
> 246810
> $ paste -sd"" odd even   # The same as the 1st
> 2o4d6d8o10

Remember, the shell strips quotes before creating the argv[] handed to
the paste process.  So 'paste -sd"" odd even' is indeed identical to
'paste -sd odd even' - by the time the quotes are stripped, you are left
with the same argv[] contents.

The space is absolutely important because it is what creates an argv of
["paste", "-sd", "", "odd", "even"] - once the quotes are stripped, you
are still left with an empty argument, but only if those quotes that
were trying to delineate an empty string weren't adjacent to anything else.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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#11828

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[adding the list back in, with permission]

On 11/03/2015 11:43 AM, Julio C. Neves wrote:
> I'm sorry to disturb you.

I have no problem replying to messages, so no need to apologize for
disturbing me.  My only problem is when messages are sent to just me
instead of the public list, because then it is a waste of resources.

> There are several responses to my question at the
> bash bug's site, but no one tells why the construction paste -s "" ...
> works, maybe because of my bad English

I don't think your English is the barrier here.  Bash quoting rules can
be tricky to learn, especially if you don't know at which point quotes
are stripped from the command line before creating the argv[] seen by
the final process.

It might help if you try this:

$ args() { echo "got $# args:"; for a; do printf '.%s.\n' "$a"; done; }
$ args a""
got 1 args:
.a.
$ args a ""
got 2 args:
.a.
..
$

Once you understand that, you will understand why "" must appear
isolated from any other text for it to produce an empty argument,
whether you are trying to pass an empty string to paste or to any other
application.

> 
> I'll give up, but if you want to post this consersation on the list fell
> free to do it.
> 
> I would like to thank you very much for your help and your time.
> 

We're trying to help. If we haven't answered your question yet, then
feel free to try asking it in a different manner.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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#11830

Eric Blake <eblake@redhat.com> writes:

> There is NO way for any program using getopt() or getopt_long() to know

s/using getopt() or getopt_long()//

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

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#11837

2015-11-03 08:29:17 -0800, julio.neves@gmail.com:
[...]
> $ paste -d "" odd even
[...]

Note that the portable and standard way to paste with no
separator is:

paste -d '\0' odd even

(no, it doesn't insert NUL characters).

not

paste -d '' odd even

which is not standard and won't work with all paste
implementations.

With traditional paste implementations:

$ paste -d '' a b
paste: no delimiters

-- 
Stephane

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