On Mon, Oct 16, 2017 at 07:26:44AM -0700, William Tu wrote:
> Allow to pass grep's option to OVS_GREP_IFELSE.
> One use case is to pass '-w' for exact match.
>
> Signed-off-by: William Tu <[email protected]>
POSIX doesn't mention a -w option, and the Autoconf manual says that it
is not portable in practice. It also says that \b is not portable in
practice.
Is there another way to accomplish what you want to do? For example,
how about HAVE_SKB_GSO_UDP[^_]? Since this is Autoconf, probably it's
necessary to double the [], as: HAVE_SKB_GSO_UDP[[^_]]
(We don't really care that much about portability to everything that
Autoconf supports, so probably we could really use -w or \b in
practice.)
This is what the Autoconf manual says:
'grep'
Portable scripts can rely on the 'grep' options '-c', '-l', '-n',
and '-v', but should avoid other options. For example, don't use
'-w', as Posix does not require it and Irix 6.5.16m's 'grep' does
not support it. Also, portable scripts should not combine '-c'
with '-l', as Posix does not allow this.
Some of the options required by Posix are not portable in practice.
Don't use 'grep -q' to suppress output, because many 'grep'
implementations (e.g., Solaris) do not support '-q'. Don't use
'grep -s' to suppress output either, because Posix says '-s' does
not suppress output, only some error messages; also, the '-s'
option of traditional 'grep' behaved like '-q' does in most modern
implementations. Instead, redirect the standard output and
standard error (in case the file doesn't exist) of 'grep' to
'/dev/null'. Check the exit status of 'grep' to determine whether
it found a match.
The QNX4 implementation fails to count lines with 'grep -c '$'',
but works with 'grep -c '^''. Other alternatives for counting
lines are to use 'sed -n '$='' or 'wc -l'.
Some traditional 'grep' implementations do not work on long input
lines. On AIX the default 'grep' silently truncates long lines on
the input before matching.
Also, many implementations do not support multiple regexps with
'-e': they either reject '-e' entirely (e.g., Solaris) or honor
only the last pattern (e.g., IRIX 6.5 and NeXT). To work around
these problems, invoke 'AC_PROG_GREP' and then use '$GREP'.
Another possible workaround for the multiple '-e' problem is to
separate the patterns by newlines, for example:
grep 'foo
bar' in.txt
except that this fails with traditional 'grep' implementations and
with OpenBSD 3.8 'grep'.
Traditional 'grep' implementations (e.g., Solaris) do not support
the '-E' or '-F' options. To work around these problems, invoke
'AC_PROG_EGREP' and then use '$EGREP', and similarly for
'AC_PROG_FGREP' and '$FGREP'. Even if you are willing to require
support for Posix 'grep', your script should not use both '-E' and
'-F', since Posix does not allow this combination.
Portable 'grep' regular expressions should use '\' only to escape
characters in the string '$()*.0123456789[\^{}'. For example,
alternation, '\|', is common but Posix does not require its support
in basic regular expressions, so it should be avoided in portable
scripts. Solaris and HP-UX 'grep' do not support it. Similarly,
the following escape sequences should also be avoided: '\<', '\>',
'\+', '\?', '\`', '\'', '\B', '\b', '\S', '\s', '\W', and '\w'.
Posix does not specify the behavior of 'grep' on binary files. An
example where this matters is using BSD 'grep' to search text that
includes embedded ANSI escape sequences for colored output to
terminals ('\033[m' is the sequence to restore normal output); the
behavior depends on whether input is seekable:
$ printf 'esc\033[mape\n' > sample
$ grep . sample
Binary file sample matches
$ cat sample | grep .
escape
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