GNU bug report logs - #20928
cut (v. 8.21), using -f option with a single column

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Kuchta, Tomasz" <t.kuchta12 <at> imperial.ac.uk>
To: "bug-coreutils <at> gnu.org" <bug-coreutils <at> gnu.org>
Subject: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 08:18:25 +0000

Hello.

I’m not sure if this is a bug - I just wanted to let you know.
Thanks,
Tomek

——

When there is more than one column and we go beyond the number of columns with the -f option, the output is empty

$ echo "test1 test2" | cut -d' ' -f1
test1
$ echo "test1 test2" | cut -d' ' -f2
test2
$ echo "test1 test2" | cut -d' ' -f3

$

—— 

When there is only one column and we go beyond 1 with the -f option, the output remains the first column

$ echo "test1" | cut -d' ' -f1
test1
$ echo "test1" | cut -d' ' -f2
test1
$ echo "test1" | cut -d' ' -f3
test1

My setup:

$ cut --version
cut (GNU coreutils) 8.21
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David M. Ihnat, David MacKenzie, and Jim Meyering.

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 14.04.2 LTS
Release:	14.04
Codename:	trusty

Message #8 received at 20928 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: "Kuchta, Tomasz" <t.kuchta12 <at> imperial.ac.uk>, 20928 <at> debbugs.gnu.org
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 16:31:00 +0100

tag 20928 notabug
close 20928
stop

On 29/06/15 09:18, Kuchta, Tomasz wrote:
> Hello.
> 
> I’m not sure if this is a bug - I just wanted to let you know.
> Thanks,
> Tomek
> 
> ——
> 
> When there is more than one column and we go beyond the number of columns with the -f option, the output is empty
> 
> $ echo "test1 test2" | cut -d' ' -f1
> test1
> $ echo "test1 test2" | cut -d' ' -f2
> test2
> $ echo "test1 test2" | cut -d' ' -f3
> 
> $
> 
> —— 
> 
> When there is only one column and we go beyond 1 with the -f option, the output remains the first column
> 
> $ echo "test1" | cut -d' ' -f1
> test1
> $ echo "test1" | cut -d' ' -f2
> test1
> $ echo "test1" | cut -d' ' -f3
> test1

That difference in behavior is there for compat reasons.
To induce the behavior you expect, you need the -s option.

thanks,
Pádraig.

Message #15 received at 20928 <at> debbugs.gnu.org (full text, mbox):

From: "Kuchta, Tomasz" <t.kuchta12 <at> imperial.ac.uk>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: "Kuchta, Tomasz" <t.kuchta12 <at> imperial.ac.uk>,
 "20928 <at> debbugs.gnu.org" <20928 <at> debbugs.gnu.org>
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 15:37:29 +0000

Hi Pádraig,

Oh, I see - thanks for letting me know.

Kind regards,
Tomek

> On 29 Jun 2015, at 16:31, Pádraig Brady <P <at> draigBrady.com> wrote:
> 
> tag 20928 notabug
> close 20928
> stop
> 
> On 29/06/15 09:18, Kuchta, Tomasz wrote:
>> Hello.
>> 
>> I’m not sure if this is a bug - I just wanted to let you know.
>> Thanks,
>> Tomek
>> 
>> ——
>> 
>> When there is more than one column and we go beyond the number of columns with the -f option, the output is empty
>> 
>> $ echo "test1 test2" | cut -d' ' -f1
>> test1
>> $ echo "test1 test2" | cut -d' ' -f2
>> test2
>> $ echo "test1 test2" | cut -d' ' -f3
>> 
>> $
>> 
>> —— 
>> 
>> When there is only one column and we go beyond 1 with the -f option, the output remains the first column
>> 
>> $ echo "test1" | cut -d' ' -f1
>> test1
>> $ echo "test1" | cut -d' ' -f2
>> test1
>> $ echo "test1" | cut -d' ' -f3
>> test1
> 
> That difference in behavior is there for compat reasons.
> To induce the behavior you expect, you need the -s option.
> 
> thanks,
> Pádraig.
> 

Message #18 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stephane Chazelas <stephane.chazelas <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 16:54:19 +0100

2015-06-29 16:31:00 +0100, Pádraig Brady:
[...]
> > When there is only one column and we go beyond 1 with the -f option, the output remains the first column
> > 
> > $ echo "test1" | cut -d' ' -f1
> > test1
> > $ echo "test1" | cut -d' ' -f2
> > test1
> > $ echo "test1" | cut -d' ' -f3
> > test1
> 
> That difference in behavior is there for compat reasons.

Yes, and that's required by POSIX
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cut.html

> To induce the behavior you expect, you need the -s option.
[...]

-s suppresses the lines that don't have the field which is
different from outputting a blank field. Here, the OP more
likely wants:

paste -d ' ' - /dev/null | cut -d' ' -f3
(or awk -F'[ ]' '{print $3}')

$ printf '%s\n' a:b c d:e | cut -d: -f2
b
c
e
$ printf '%s\n' a:b c d:e | cut -sd: -f2
b
e
$ printf '%s\n' a:b c d:e | paste -d: - /dev/null | cut -d: -f2
b

e

-- 
Stephane

Message #21 received at 20928 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Stephane Chazelas <stephane.chazelas <at> gmail.com>, 
 20928 <at> debbugs.gnu.org
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 17:25:11 +0100

On 29/06/15 16:54, Stephane Chazelas wrote:
> 2015-06-29 16:31:00 +0100, Pádraig Brady:
> [...]
>>> When there is only one column and we go beyond 1 with the -f option, the output remains the first column
>>>
>>> $ echo "test1" | cut -d' ' -f1
>>> test1
>>> $ echo "test1" | cut -d' ' -f2
>>> test1
>>> $ echo "test1" | cut -d' ' -f3
>>> test1
>>
>> That difference in behavior is there for compat reasons.
> 
> Yes, and that's required by POSIX
> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cut.html
> 
>> To induce the behavior you expect, you need the -s option.
> [...]
> 
> -s suppresses the lines that don't have the field which is
> different from outputting a blank field. Here, the OP more
> likely wants:
> 
> paste -d ' ' - /dev/null | cut -d' ' -f3
> (or awk -F'[ ]' '{print $3}')
> 
> $ printf '%s\n' a:b c d:e | cut -d: -f2
> b
> c
> e
> $ printf '%s\n' a:b c d:e | cut -sd: -f2
> b
> e
> $ printf '%s\n' a:b c d:e | paste -d: - /dev/null | cut -d: -f2
> b
> 
> e

Good point. Or to better support field ranges:

$ printf '%s\n' a:b c d:e | sed 's/^[^:]*$/&:/' | cut -d: -f2-
b

e

cheers,
Pádraig.

Message #24 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stephane Chazelas <stephane.chazelas <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Mon, 29 Jun 2015 17:42:53 +0100

2015-06-29 17:25:11 +0100, Pádraig Brady:
[...]
> > $ printf '%s\n' a:b c d:e | paste -d: - /dev/null | cut -d: -f2
> > b
> > 
> > e
> 
> Good point. Or to better support field ranges:
> 
> $ printf '%s\n' a:b c d:e | sed 's/^[^:]*$/&:/' | cut -d: -f2-
> b
> 
> e
[...]

Maybe better as:

$ printf '%b\n' a:b 'P\0341draig' d:e | sed '/:/!s/$/:/' | cut -d: -f2-

so it also works on lines that contain invalid characters.

-- 
Stephane

Message #27 received at 20928 <at> debbugs.gnu.org (full text, mbox):

From: "Kuchta, Tomasz" <t.kuchta12 <at> imperial.ac.uk>
To: "20928 <at> debbugs.gnu.org" <20928 <at> debbugs.gnu.org>
Subject: Re: bug#20928: cut (v. 8.21), using -f option with a single column
Date: Tue, 30 Jun 2015 08:03:38 +0000

Pádraig, Stephane - thanks a lot for your help and quick response!
Tomek

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