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(Shell Substitutions): Fix typo in case statement.

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Warn about newline stripping in `` and $().  Update Solaris
version to 9.
(Limitations of Builtins): Use expr "X...", not expr "x...", as
X insulates us from future changes to Posix.
(Limitations of Usual Tools): For AS_DIRNAME, warn about newline
stripping.
This commit is contained in:
Paul Eggert 2005-01-21 00:03:40 +00:00
parent 4c38a43946
commit d01f64e300
1 changed files with 18 additions and 6 deletions
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24
doc/autoconf.texi
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@ -10002,7 +10002,7 @@ For instance, the following code:
@example
case "$given_srcdir" in
.) top_srcdir="`echo "$dots" | sed 's,/$,,'`"
.) top_srcdir="`echo "$dots" | sed 's,/$,,'`" ;;
*) top_srcdir="$dots$given_srcdir" ;;
esac
@end example
@ -10012,7 +10012,7 @@ is more readable when written as:
@example
case $given_srcdir in
.) top_srcdir=`echo "$dots" | sed 's,/$,,'`
.) top_srcdir=`echo "$dots" | sed 's,/$,,'` ;;
*) top_srcdir=$dots$given_srcdir ;;
esac
@end example
@ -10190,6 +10190,11 @@ test "$@{var+set@}" = set || var=@var{@{value@}}
@item `@var{commands}`
@cindex `@var{commands}`
@cindex Command Substitution
Posix requires shells to trim all trailing newlines from command
output before substituting it, so assignments like
@samp{dir=`AS_DIRNAME(["$file"])`} will not work as expected if the
directory of @samp{$file} ends in a newline.
While in general it makes no sense, do not substitute a single builtin
with side effects, because Ash 0.2, trying to optimize, does not fork a
subshell to perform the command.
@ -10210,14 +10215,17 @@ The result of @samp{foo=`exit 1`} is left as an exercise to the reader.
@item $(@var{commands})
@cindex $(@var{commands})
This construct is meant to replace @samp{`@var{commands}`}; they can be
This construct is meant to replace @samp{`@var{commands}`},
and it has most of the problems listed under @code{`@var{commands}`}.
This construct can be
nested while this is impossible to do portably with back quotes.
Unfortunately it is not yet widely supported. Most notably, even recent
Unfortunately it is not yet universally supported. Most notably, even recent
releases of Solaris don't support it:
@example
$ @kbd{showrev -c /bin/sh | grep version}
Command version: SunOS 5.8 Generic 109324-02 February 2001
Command version: SunOS 5.9 Generic May 2002
$ @kbd{echo $(echo blah)}
syntax error: `(' unexpected
@end example
@ -11155,7 +11163,7 @@ expr "$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
or better yet
@example
expr "x$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
expr "X$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
@var{action}
@end example
@ -11481,6 +11489,10 @@ dir=`dirname "$file"` # This is not portable.
dir=`AS_DIRNAME(["$file"])` # This is more portable.
@end example
Unfortunately, neither of the above commands work if @code{$file}'s
directory name ends in newline, since @samp{`@dots{}`} removes all
trailing newlines.
@noindent
This handles a few subtleties in the standard way required by
Posix. For example, under UN*X, should @samp{dirname //1} give