GNU bug report logs - #11809
document "So how do we just simply make a backup file?"

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

From: jidanni <at> jidanni.org
To: bug-coreutils <at> gnu.org
Subject: document "So how do we just simply make a backup file?"
Date: Thu, 28 Jun 2012 23:30:59 +0800

(info "(coreutils) Backup options") should add some examples, for
"So how do we make a backup file of m?"
$ ls
m
$ cp -b m m #no go
$ cp m n
$ mv -b n m

Message #8 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: jidanni <at> jidanni.org
Cc: 11809 <at> debbugs.gnu.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Thu, 28 Jun 2012 18:01:31 +0200

jidanni <at> jidanni.org wrote:
> (info "(coreutils) Backup options") should add some examples, for
> "So how do we make a backup file of m?"
> $ ls
> m
> $ cp -b m m #no go

Thanks for the suggestion.
I use this zsh/bash shell function:

backup ()
{
  local i
  for i in "$@"; do
    command cp -bf "$i" "$i"
  done
}

but as I inserted the above, I realize it's buggy.
It doesn't propagate failure like you'd expect,
so here's a better one:

backup()
{
  local i fail=0
  for i in "$@"; do
    command cp -bf -- "$i" "$i" || fail=1
  done
  return $fail
}

That's already almost what info coreutils says:

  Make a backup of each file that would otherwise be overwritten or removed.
  As a special case, @command{cp} makes a backup of @var{source} when the force
  and backup options are given and @var{source} and @var{dest} are the same
  name for an existing, regular file.  One useful application of this
  combination of options is this tiny Bourne shell script:

  @example
  #!/bin/sh
  # Usage: backup FILE...
  # Create a @sc{gnu}-style backup of each listed FILE.
  for i; do
    cp --backup --force -- "$i" "$i"
  done
  @end example

I'll adjust that to reflect the above improvement:
Do you think that's enough?

> $ cp m n
> $ mv -b n m

Message #11 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: jidanni <at> jidanni.org
To: jim <at> meyering.net
Cc: 11809 <at> debbugs.gnu.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 00:16:07 +0800

OK but (info "(coreutils) Backup options") should also link back to the exact
cp -b spot, else most folks will miss it.

P.S., There _is_ an easier way of making backups of several files,
But there is a bug, one has to do it one at a time despite -b. Bug bug bug. 

$ \cp -fb h k l .
cp: `h' and `./h' are the same file
cp: `k' and `./k' are the same file
cp: `l' and `./l' are the same file
$ \cp -fb h h
$

Message #14 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: jidanni <at> jidanni.org
Cc: 11809 <at> debbugs.gnu.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 07:52:00 +0200

jidanni <at> jidanni.org wrote:
> OK but (info "(coreutils) Backup options") should also link back to the exact
> cp -b spot, else most folks will miss it.
>
> P.S., There _is_ an easier way of making backups of several files,
> But there is a bug, one has to do it one at a time despite -b. Bug bug bug.
>
> $ \cp -fb h k l .
> cp: `h' and `./h' are the same file
> cp: `k' and `./k' are the same file
> cp: `l' and `./l' are the same file
> $ \cp -fb h h
> $

No, that was deliberate.

I deliberately restricted the "make backup only" functionality to the
very limited case that is documented.  Widening the semantics, as you
suggest above, seems like it would make this "feature" more likely to
be discovered accidentally -- with data loss, when both originals and
backups are removed.

If people think the make-backup-only feature is useful enough for
multiple files, then we can consider adding an --only-backup option,
(better name welcome, but it cannot start with "--backup") rather than
co-opting the --force --backup combination and requiring a script to
process more than one at a time.

Message #17 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: jidanni <at> jidanni.org
To: jim <at> meyering.net
Cc: 11809 <at> debbugs.gnu.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 16:11:45 +0800

JM> I deliberately restricted the "make backup only" functionality to the
JM> very limited case that is documented.
Well you had better explicitly document that it does not work with
all forms in the cp SYNOPSIS, else people will think it is broken...

Message #20 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: jidanni <at> jidanni.org
Cc: 11809 <at> debbugs.gnu.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 10:48:30 +0200

Jim Meyering wrote:
> jidanni <at> jidanni.org wrote:
>> (info "(coreutils) Backup options") should add some examples, for
>> "So how do we make a backup file of m?"
>> $ ls
>> m
>> $ cp -b m m #no go
>
> Thanks for the suggestion.
> I use this zsh/bash shell function:
>
> backup ()
> {
>   local i
>   for i in "$@"; do
>     command cp -bf "$i" "$i"
>   done
> }
>
> but as I inserted the above, I realize it's buggy.
> It doesn't propagate failure like you'd expect,
> so here's a better one:
>
> backup()
> {
>   local i fail=0
>   for i in "$@"; do
>     command cp -bf -- "$i" "$i" || fail=1
>   done
>   return $fail
> }
>
> That's already almost what info coreutils says:
>
>   Make a backup of each file that would otherwise be overwritten or removed.
>   As a special case, @command{cp} makes a backup of @var{source} when the force
>   and backup options are given and @var{source} and @var{dest} are the same
>   name for an existing, regular file.  One useful application of this
>   combination of options is this tiny Bourne shell script:
>
>   @example
>   #!/bin/sh
>   # Usage: backup FILE...
>   # Create a @sc{gnu}-style backup of each listed FILE.
>   for i; do
>     cp --backup --force -- "$i" "$i"
>   done
>   @end example
>
> I'll adjust that to reflect the above improvement:
> Do you think that's enough?

Here's the doc patch I suggested, but I'll hold off for now.
I'd like to hear if anyone thinks it's worth adding a new option,
which would obviate such a script.

From 3a1bc89c3e3ca277be49d4fceb60abb57e3fc9d2 Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering <at> redhat.com>
Date: Fri, 29 Jun 2012 10:45:31 +0200
Subject: [PATCH] doc: improve sample backup script

* doc/coreutils.texi (cp invocation): Make the backup script exit
with an accurate reflection of any failure.
---
 doc/coreutils.texi | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 08ef2d8..5207c44 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -7675,9 +7675,11 @@ cp invocation
 #!/bin/sh
 # Usage: backup FILE...
 # Create a @sc{gnu}-style backup of each listed FILE.
+fail=0
 for i; do
-  cp --backup --force -- "$i" "$i"
+  cp --backup --force -- "$i" "$i" || fail=1
 done
+exit $fail
 @end example

 @item --copy-contents
--
1.7.11.1.59.gbc9e7dd

Message #23 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Jim Meyering <jim <at> meyering.net>
Cc: 11809 <at> debbugs.gnu.org, jidanni <at> jidanni.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 11:30:38 +0200

On 06/29/2012 10:48 AM, Jim Meyering wrote:
> Here's the doc patch I suggested, but I'll hold off for now.
> I'd like to hear if anyone thinks it's worth adding a new option,
> which would obviate such a script.

I think it's okay, that special backup case is described in the info
page of cp twice anyway.

> diff --git a/doc/coreutils.texi b/doc/coreutils.texi
> index 08ef2d8..5207c44 100644
> --- a/doc/coreutils.texi
> +++ b/doc/coreutils.texi
> @@ -7675,9 +7675,11 @@ cp invocation
>  #!/bin/sh
>  # Usage: backup FILE...
>  # Create a @sc{gnu}-style backup of each listed FILE.
> +fail=0
>  for i; do
> -  cp --backup --force -- "$i" "$i"
> +  cp --backup --force -- "$i" "$i" || fail=1
>  done
> +exit $fail
>  @end example
> 
>  @item --copy-contents

When we speak of "backup", then maybe "--preserve=all" would be nice.

BTW: that special backup case accepts -a which includes both -d and -R
which both are maybe not ideal if you speak about a backup of a regular
file. The former treats symlinks specially, and the latter is designed
to recurse into directories - both may be misleading (although -d may
make some sense in certain situation when creating a backup of a
symlink). WDYT?

Have a nice day,
Berny

Message #26 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 11809 <at> debbugs.gnu.org, jidanni <at> jidanni.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Fri, 29 Jun 2012 12:22:01 +0200

Bernhard Voelker wrote:
> On 06/29/2012 10:48 AM, Jim Meyering wrote:
>> Here's the doc patch I suggested, but I'll hold off for now.
>> I'd like to hear if anyone thinks it's worth adding a new option,
>> which would obviate such a script.
>
> I think it's okay, that special backup case is described in the info
> page of cp twice anyway.
>
>> diff --git a/doc/coreutils.texi b/doc/coreutils.texi
>> index 08ef2d8..5207c44 100644
>> --- a/doc/coreutils.texi
>> +++ b/doc/coreutils.texi
>> @@ -7675,9 +7675,11 @@ cp invocation
>>  #!/bin/sh
>>  # Usage: backup FILE...
>>  # Create a @sc{gnu}-style backup of each listed FILE.
>> +fail=0
>>  for i; do
>> -  cp --backup --force -- "$i" "$i"
>> +  cp --backup --force -- "$i" "$i" || fail=1
>>  done
>> +exit $fail
>>  @end example
>>
>>  @item --copy-contents
>
> When we speak of "backup", then maybe "--preserve=all" would be nice.
>
> BTW: that special backup case accepts -a which includes both -d and -R
> which both are maybe not ideal if you speak about a backup of a regular
> file. The former treats symlinks specially, and the latter is designed
> to recurse into directories - both may be misleading (although -d may
> make some sense in certain situation when creating a backup of a
> symlink). WDYT?

Adding --preserve=all sounds like a good idea.
Thanks.

Allowing this little script to work also for non-regular files
seems like it'd be useful, too.  But it's beginning to look as if
this combination of options is both useful and involved enough that
the functionality should be provided by a new --only-backup option.

Message #29 received at 11809 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 11809 <at> debbugs.gnu.org, jidanni <at> jidanni.org
Subject: Re: bug#11809: document "So how do we just simply make a backup file?"
Date: Sat, 30 Jun 2012 11:52:57 +0200

Jim Meyering wrote:
> Bernhard Voelker wrote:
>> On 06/29/2012 10:48 AM, Jim Meyering wrote:
>>> Here's the doc patch I suggested, but I'll hold off for now.
>>> I'd like to hear if anyone thinks it's worth adding a new option,
>>> which would obviate such a script.
>>
>> I think it's okay, that special backup case is described in the info
>> page of cp twice anyway.
>>
>>> diff --git a/doc/coreutils.texi b/doc/coreutils.texi
>>> index 08ef2d8..5207c44 100644
>>> --- a/doc/coreutils.texi
>>> +++ b/doc/coreutils.texi
>>> @@ -7675,9 +7675,11 @@ cp invocation
>>>  #!/bin/sh
>>>  # Usage: backup FILE...
>>>  # Create a @sc{gnu}-style backup of each listed FILE.
>>> +fail=0
>>>  for i; do
>>> -  cp --backup --force -- "$i" "$i"
>>> +  cp --backup --force -- "$i" "$i" || fail=1
>>>  done
>>> +exit $fail
>>>  @end example
>>>
>>>  @item --copy-contents
>>
>> When we speak of "backup", then maybe "--preserve=all" would be nice.
>>
>> BTW: that special backup case accepts -a which includes both -d and -R
>> which both are maybe not ideal if you speak about a backup of a regular
>> file. The former treats symlinks specially, and the latter is designed
>> to recurse into directories - both may be misleading (although -d may
>> make some sense in certain situation when creating a backup of a
>> symlink). WDYT?
>
> Adding --preserve=all sounds like a good idea.
> Thanks.
>
> Allowing this little script to work also for non-regular files
> seems like it'd be useful, too.  But it's beginning to look as if
> this combination of options is both useful and involved enough that
> the functionality should be provided by a new --only-backup option.

I went ahead and pushed this:

From 5f6c22fceedd0d350e1a8246d4d73840de666c7e Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering <at> redhat.com>
Date: Fri, 29 Jun 2012 10:45:31 +0200
Subject: [PATCH] doc: improve sample backup script

* doc/coreutils.texi (cp invocation): Make the backup script exit
with an accurate reflection of any failure.
Also, add --preserve=all.

Improved-by: Bernhard Voelker
---
 doc/coreutils.texi | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 08ef2d8..954a1f8 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -7675,9 +7675,11 @@ cp invocation
 #!/bin/sh
 # Usage: backup FILE...
 # Create a @sc{gnu}-style backup of each listed FILE.
+fail=0
 for i; do
-  cp --backup --force -- "$i" "$i"
+  cp --backup --force --preserve=all -- "$i" "$i" || fail=1
 done
+exit $fail
 @end example

 @item --copy-contents
--
1.7.11.1.104.ge7b44f1

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