diffutils: patch and Tradition
10.13 GNU 'patch' and Traditional 'patch'
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The current version of GNU 'patch' normally follows the POSIX standard.
⇒patch and POSIX, for the few exceptions to this general rule.
Unfortunately, POSIX redefined the behavior of 'patch' in several
important ways. You should be aware of the following differences if you
must interoperate with traditional 'patch', or with GNU 'patch' version
2.1 and earlier.
* In traditional 'patch', the '-p' option's operand was optional, and
a bare '-p' was equivalent to '-p0'. The '-p' option now requires
an operand, and '-p 0' is now equivalent to '-p0'. For maximum
compatibility, use options like '-p0' and '-p1'.
Also, traditional 'patch' simply counted slashes when stripping
path prefixes; 'patch' now counts pathname components. That is, a
sequence of one or more adjacent slashes now counts as a single
slash. For maximum portability, avoid sending patches containing
'//' in file names.
* In traditional 'patch', backups were enabled by default. This
behavior is now enabled with the '--backup' ('-b') option.
Conversely, in POSIX 'patch', backups are never made, even when
there is a mismatch. In GNU 'patch', this behavior is enabled with
the '--no-backup-if-mismatch' option, or by conforming to POSIX.
The '-b SUFFIX' option of traditional 'patch' is equivalent to the
'-b -z SUFFIX' options of GNU 'patch'.
* Traditional 'patch' used a complicated (and incompletely
documented) method to intuit the name of the file to be patched
from the patch header. This method did not conform to POSIX, and
had a few gotchas. Now 'patch' uses a different, equally
complicated (but better documented) method that is optionally
POSIX-conforming; we hope it has fewer gotchas. The two methods
are compatible if the file names in the context diff header and the
'Index:' line are all identical after prefix-stripping. Your patch
is normally compatible if each header's file names all contain the
same number of slashes.
* When traditional 'patch' asked the user a question, it sent the
question to standard error and looked for an answer from the first
file in the following list that was a terminal: standard error,
standard output, '/dev/tty', and standard input. Now 'patch' sends
questions to standard output and gets answers from '/dev/tty'.
Defaults for some answers have been changed so that 'patch' never
goes into an infinite loop when using default answers.
* Traditional 'patch' exited with a status value that counted the
number of bad hunks, or with status 1 if there was real trouble.
Now 'patch' exits with status 1 if some hunks failed, or with 2 if
there was real trouble.
* Limit yourself to the following options when sending instructions
meant to be executed by anyone running GNU 'patch', traditional
'patch', or a 'patch' that conforms to POSIX. Spaces are
significant in the following list, and operands are required.
-c
-d DIR
-D DEFINE
-e
-l
-n
-N
-o OUTFILE
-pNUM
-R
-r REJECTFILE
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