+2006-05-22 Paul Eggert <eggert@cs.ucla.edu>,
+ Ralf Wildenhues <Ralf.Wildenhues@gmx.de>,
+ Stepan Kasal <kasal@ucw.cz>
+
+ * doc/autoconf.texi (Particular Programs): Do not promise that
+ we always prefer the GNU version of the program, and that we
+ search according to PATH; both rules can have exceptions.
+ Update description of AC_PROG_GREP, AC_PROG_EGREP, AC_PROG_FGREP,
+ AC_PROG_SED. Move descriptions of limitations
+ to the Limitations of Usual Tools section.
+ (Limitations of Usual Tools) <sed>: Mention script length
+ limitations with Solaris /usr/ucb/sed.
+ <grep>: Fix wording for empty alternative. Mention that -c and
+ -l should not be combined, and that -E and -F should not be
+ combined.
+
2006-05-21 Paul Eggert <eggert@cs.ucla.edu>
and Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
@defmac AC_PROG_GREP
@acindex{PROG_GREP}
@ovindex GREP
-On AIX the default @code{grep} silently truncates long lines on the
-input before matching. On Solaris, @code{/usr/bin/grep} does not
-understand the @option{-e} option. On NeXT, @code{grep} understands only a
-single @option{-e} option. This macro looks for @sc{gnu} Grep or
-else the best available @code{grep} or @code{ggrep} in the user's
-@env{PATH} which accepts the longest input lines possible, and which
-accepts and respects multiple @option{-e} options. Set the
-output variable @code{GREP} to whatever is chosen.
+Look for the best available @code{grep} or @code{ggrep} that accepts the
+longest input lines possible, and that supports multiple @option{-e} options.
+Set the output variable @code{GREP} to whatever is chosen.
+@xref{Limitations of Usual Tools}, for more information about
+portability problems with the @command{grep} command family.
@end defmac
@defmac AC_PROG_EGREP
@acindex{PROG_EGREP}
@ovindex EGREP
-Check whether @code{$GREP -E} works, or else search the user's
-@env{PATH} for @code{egrep}, and @code{gegrep}, in that order, and set
-output variable @code{EGREP} to the one that accepts the longest input
-lines.
+Check whether @code{$GREP -E} works, or else look for the best available
+@code{egrep} or @code{gegrep} that accepts the longest input lines possible.
+Set the output variable @code{EGREP} to whatever is chosen.
@end defmac
@defmac AC_PROG_FGREP
@acindex{PROG_FGREP}
@ovindex FGREP
-Check whether @code{$GREP -F} works, or else search the user's
-@env{PATH} for @code{fgrep}, and @code{gfgrep}, in that order, and set
-output variable @code{FGREP} to the one that accepts the longest input
-lines.
+Check whether @code{$GREP -F} works, or else look for the best available
+@code{fgrep} or @code{gfgrep} that accepts the longest input lines possible.
+Set the output variable @code{FGREP} to whatever is chosen.
@end defmac
@defmac AC_PROG_INSTALL
@defmac AC_PROG_SED
@acindex{PROG_SED}
@ovindex SED
-Set output variable @code{SED} to a Sed implementation on @env{PATH} that
-truncates as few characters as possible. If @sc{gnu} Sed is found,
-use that instead.
+Set output variable @code{SED} to a Sed implementation that conforms to
+Posix and does not have arbitrary length limits. Report an error if no
+acceptable Sed is found. @xref{Limitations of Usual Tools}, for more
+information about portability problems with Sed.
@end defmac
@defmac AC_PROG_YACC
characters in the string @samp{$()*+.?[\^@{|}. For example, @samp{\@}}
is not portable, even though it typically matches @samp{@}}.
-The empty alternative is not portable, use @samp{?} instead. For
+The empty alternative is not portable. Use @samp{?} instead. For
instance with Digital Unix v5.0:
@example
Portable scripts can rely on the @command{grep} options @option{-c},
@option{-l}, @option{-n}, and @option{-v}, but should avoid other
options. For example, don't use @option{-w}, as Posix does not require
-it and Irix 6.5.16m's @command{grep} does not support it.
+it and Irix 6.5.16m's @command{grep} does not support it. Also,
+portable scripts should not combine @option{-c} with @option{-l},
+as Posix does not allow this.
Some of the options required by Posix are not portable in practice.
Don't use @samp{grep -q} to suppress output, because many @command{grep}
status of @code{grep} to determine whether it found a match.
Some traditional @command{grep} implementations do not work on long
-input lines. Also, many implementations do not support multiple regexps
+input lines. On AIX the default @code{grep} silently truncates long
+lines on the input before matching.
+
+Also, many implementations do not support multiple regexps
with @option{-e}: they either reject @option{-e} entirely (e.g., Solaris)
-or honor only the last pattern (e.g., @acronym{IRIX} 6.5). To
+or honor only the last pattern (e.g., @acronym{IRIX} 6.5 and NeXT). To
work around these problems, invoke @code{AC_PROG_GREP} and then use
@code{$GREP}.
Traditional @command{grep} implementations (e.g., Solaris) do not
support the @option{-E} or @option{-F} options. To work around these
problems, invoke @code{AC_PROG_EGREP} and then use @code{$EGREP}, and
-similarly for @code{AC_PROG_FGREP} and @code{$FGREP}.
+similarly for @code{AC_PROG_FGREP} and @code{$FGREP}. Even if you are
+willing to require support for Posix @command{grep}, your script should
+not use both @option{-E} and @option{-F}, since Posix does not allow
+this combination.
Portable @command{grep} regular expressions should use @samp{\} only to
escape characters in the string @samp{$()*.0123456789[\^@{@}}. For example,
(not counting @samp{:} commands) and
48 labels, which can not be circumvented by using more than one script
file. It can execute up to 19 reads with the @samp{r} command per cycle.
+Solaris @command{/usr/ucb/sed} rejects usages that exceed an limit of
+about 6000 bytes for the internal representation of commands.
Avoid redundant @samp{;}, as some @command{sed} implementations, such as
Net@acronym{BSD} 1.4.2's, incorrectly try to interpret the second
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