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cp: change --attributes-only to not truncate existing files

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* src/copy.c (copy_reg): Don't truncate an existing file,
to support copying attributes between existing files.
The original use case only considered creating new files,
and it would be a very unusual use case to be relying
on the truncating behavior.
* doc/coreutils.texi (cp invocation): Mention the non
truncating behavior.
* tests/cp/attr-existing: A new test to ensure O_TRUNC skipped.
* tests/Makefile.am: Reference the new test.
* NEWS: Mention the change in behavior.
This commit is contained in:
Pádraig Brady
2012-04-12 12:47:30 +01:00
parent 7e0ef7c035
commit 3d53e7fe1c
5 changed files with 41 additions and 4 deletions
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5
NEWS
View File

@@ -2,6 +2,11 @@ GNU coreutils NEWS -*- outline -*-
* Noteworthy changes in release ?.? (????-??-??) [?]
** Changes in behavior
cp --attributes-only no longer truncates any existing destination file,
allowing for more general copying of attributes from one file to another.
* Noteworthy changes in release 8.16 (2012-03-26) [stable]

6
doc/coreutils.texi
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@@ -7649,9 +7649,9 @@ Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
@itemx --attributes-only
@opindex --attributes-only
Preserve the specified attributes of the original files in the copy,
but do not copy any data. See the @option{--preserve} option for
controlling which attributes to copy.
Copy only the specified attributes of the source file to the destination.
If the destination already exists, do not alter its contents.
See the @option{--preserve} option for controlling which attributes to copy.
@item -b
@itemx @w{@kbd{--backup}[=@var{method}]}

4
src/copy.c
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@@ -826,7 +826,9 @@ copy_reg (char const *src_name, char const *dst_name,
by the specs for both cp and mv. */
if (! *new_dst)
{
dest_desc = open (dst_name, O_WRONLY | O_TRUNC | O_BINARY);
int open_flags =
O_WRONLY | O_BINARY | (x->data_copy_required ? O_TRUNC : 0);
dest_desc = open (dst_name, open_flags);
dest_errno = errno;
/* When using cp --preserve=context to copy to an existing destination,

1
tests/Makefile.am
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@@ -320,6 +320,7 @@ TESTS = \
chown/separator \
cp/abuse \
cp/acl \
cp/attr-existing \
cp/backup-1 \
cp/backup-dir \
cp/backup-is-src \

29
tests/cp/attr-existing Executable file
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@@ -0,0 +1,29 @@
#!/bin/sh
# Make sure cp --attributes-only doesn't truncate existing data
# Copyright 2012 Free Software Foundation, Inc.
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
. "${srcdir=.}/init.sh"; path_prepend_ ../src
print_ver_ cp
printf '1' > file1
printf '2' > file2
printf '2' > file2.exp
cp --attributes-only file1 file2 || fail=1
cmp file2 file2.exp || fail=1
Exit $fail