From: Eric Blake <eblake@redhat.com>
Date: Wed, 25 Aug 2010 22:54:42 +0000 (-0600)
Subject: docs: mention cost of globbing during variable expansion
X-Git-Tag: v2.68~52
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cb27df430d86d5a16bc1f210d36e29400369dbc2;p=thirdparty%2Fautoconf.git

docs: mention cost of globbing during variable expansion

* doc/autoconf.texi (Shell Substitutions) <${var=literal}>:
Recommend quoting substitutions that might trigger globbing.
(Limitations of Builtins) <:>: Likewise.
* bin/autoconf.as: Follow our own advice.
* lib/autoconf/functions.m4 (AC_FUNC_SELECT_ARGTYPES): Likewise.
* lib/autoconf/general.m4 (_AC_INIT_PARSE_ARGS): Likewise.
* lib/autoconf/status.m4 (AC_OUTPUT): Likewise.
* lib/autotest/general.m4 (_AT_FINISH): Likewise.
* lib/m4sugar/m4sh.m4 (AS_TMPDIR): Likewise.
* tests/autotest.at (parallel autotest and signal handling):
Likewise.
* tests/c.at (AC_OPENMP and C, AC_OPENMP and C++): Likewise.
* tests/foreign.at (shtool): Likewise.
* tests/fortran.at: Likewise.
* tests/tools.at (autom4te preselections): Likewise.
* tests/torture.at (VPATH): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>
---

diff --git a/ChangeLog b/ChangeLog
index 569d7ad9..ae486c52 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,23 @@
 2010-08-25  Eric Blake  <eblake@redhat.com>
 
+	docs: mention cost of globbing during variable expansion
+	* doc/autoconf.texi (Shell Substitutions) <${var=literal}>:
+	Recommend quoting substitutions that might trigger globbing.
+	(Limitations of Builtins) <:>: Likewise.
+	* bin/autoconf.as: Follow our own advice.
+	* lib/autoconf/functions.m4 (AC_FUNC_SELECT_ARGTYPES): Likewise.
+	* lib/autoconf/general.m4 (_AC_INIT_PARSE_ARGS): Likewise.
+	* lib/autoconf/status.m4 (AC_OUTPUT): Likewise.
+	* lib/autotest/general.m4 (_AT_FINISH): Likewise.
+	* lib/m4sugar/m4sh.m4 (AS_TMPDIR): Likewise.
+	* tests/autotest.at (parallel autotest and signal handling):
+	Likewise.
+	* tests/c.at (AC_OPENMP and C, AC_OPENMP and C++): Likewise.
+	* tests/foreign.at (shtool): Likewise.
+	* tests/fortran.at: Likewise.
+	* tests/tools.at (autom4te preselections): Likewise.
+	* tests/torture.at (VPATH): Likewise.
+
 	m4sh: fix some namespace safety issues
 	* lib/m4sugar/m4sh.m4 (_AS_SHELL_SANITIZE): Avoid problems if
 	as_myself is inherited from environment.
diff --git a/bin/autoconf.as b/bin/autoconf.as
index aa7fe6b5..dca46068 100644
--- a/bin/autoconf.as
+++ b/bin/autoconf.as
@@ -85,7 +85,7 @@ exit_missing_arg='
 # restore font-lock: '
 
 # Variables.
-: ${AUTOM4TE='@bindir@/@autom4te-name@'}
+: "${AUTOM4TE='@bindir@/@autom4te-name@'}"
 autom4te_options=
 outfile=
 verbose=false
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index a20be769..28637c51 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15398,10 +15398,36 @@ Similarly for $@{@var{var}:=@var{value}@}, $@{@var{var}:?@var{value}@}, etc.
 
 @item $@{@var{var}=@var{literal}@}
 @cindex $@{@var{var}=@var{literal}@}
-Be sure to quote:
+When using @samp{$@{@var{var}=@var{value}@}} to assign a default value
+to @var{var}, remember that even though the assignment to @var{var} does
+not undergo file name expansion, the result of the variable expansion
+does.  In particular, when using @command{:} followed by unquoted
+variable expansion for the side effect of setting a default value, if
+either @samp{value} or the prior contents of @samp{$var} contains
+globbing characters, the shell has to spend time performing file name
+expansion and field splitting even though those results will not be
+used.  Therefore, it is a good idea to use double quotes when performing
+default initialization.
 
 @example
-: $@{var='Some words'@}
+$ time bash -c ': "$@{a=/usr/bin/*@}"; echo "$a"'
+/usr/bin/*
+
+real	0m0.005s
+user	0m0.002s
+sys	0m0.003s
+$ time bash -c ': $@{a=/usr/bin/*@}; echo "$a"'
+/usr/bin/*
+
+real	0m0.039s
+user	0m0.026s
+sys	0m0.009s
+@end example
+
+Use quotes if @var{literal} contains more than one shell word:
+
+@example
+: "$@{var='Some words'@}"
 @end example
 
 @noindent
@@ -15441,7 +15467,7 @@ running
 
 @example
 default="yu,yaa"
-: $@{var="$default"@}
+: "$@{var="$default"@}"
 @end example
 
 @noindent
@@ -15467,7 +15493,7 @@ One classic incarnation of this bug is:
 
 @example
 default="a b c"
-: $@{list="$default"@}
+: "$@{list="$default"@}"
 for c in $list; do
   echo $c
 done
@@ -15720,7 +15746,7 @@ If the default value is a literal and does not contain any closing
 brace, use:
 
 @example
-: $@{var='my literal'@}
+: "$@{var='my literal'@}"
 @end example
 
 @item
@@ -15729,7 +15755,7 @@ the variable being initialized is not intended to be IFS-split
 (i.e., it's not a list), then use:
 
 @example
-: $@{var="$default"@}
+: "$@{var="$default"@}"
 @end example
 
 @item
@@ -17432,6 +17458,11 @@ exit status of failure, which is correct for @command{false}, but not
 for @command{true}.
 @end quotation
 
+Remember that even though @samp{:} ignores its arguments, it still takes
+time to compute those arguments.  It is a good idea to use double quotes
+around any arguments to @samp{:} to avoid time spent in field splitting
+and file name expansion.
+
 
 @anchor{unset}
 @item @command{unset}
@@ -18259,7 +18290,7 @@ Here is sample code to create a new temporary directory safely:
 # Create a temporary directory $tmp in $TMPDIR (default /tmp).
 # Use mktemp if possible; otherwise fall back on mkdir,
 # with $RANDOM to make collisions less likely.
-: $@{TMPDIR=/tmp@}
+: "$@{TMPDIR=/tmp@}"
 @{
   tmp=`
     (umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null
diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index d7058c8a..7e69d461 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -1453,7 +1453,7 @@ AC_CACHE_CHECK([types of arguments for select],
  done
 done
 # Provide a safe default value.
-: ${ac_cv_func_select_args='int,int *,struct timeval *'}
+: "${ac_cv_func_select_args='int,int *,struct timeval *'}"
 ])
 ac_save_IFS=$IFS; IFS=','
 set dummy `echo "$ac_cv_func_select_args" | sed 's/\*/\*/g'`
diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 99cc3262..c6f39807 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -900,7 +900,7 @@ Try `$[0] --help' for more information])
     AC_MSG_WARN([you should use --build, --host, --target])
     expr "x$ac_option" : "[.*[^-._$as_cr_alnum]]" >/dev/null &&
       AC_MSG_WARN([invalid host type: $ac_option])
-    : ${build_alias=$ac_option} ${host_alias=$ac_option} ${target_alias=$ac_option}
+    : "${build_alias=$ac_option} ${host_alias=$ac_option} ${target_alias=$ac_option}"
     ;;
 
   esac
diff --git a/lib/autoconf/status.m4 b/lib/autoconf/status.m4
index 56190a42..9bd0a507 100644
--- a/lib/autoconf/status.m4
+++ b/lib/autoconf/status.m4
@@ -1271,7 +1271,7 @@ m4_ifdef([_AC_SEEN_CONFIG(HEADERS)], [DEFS=-DHAVE_CONFIG_H], [AC_OUTPUT_MAKE_DEF
 dnl Commands to run before creating config.status.
 AC_OUTPUT_COMMANDS_PRE()dnl
 
-: ${CONFIG_STATUS=./config.status}
+: "${CONFIG_STATUS=./config.status}"
 ac_write_fail=0
 ac_clean_files_save=$ac_clean_files
 ac_clean_files="$ac_clean_files $CONFIG_STATUS"
diff --git a/lib/autotest/general.m4 b/lib/autotest/general.m4
index ef76e63c..e639ce6d 100644
--- a/lib/autotest/general.m4
+++ b/lib/autotest/general.m4
@@ -847,7 +847,7 @@ do
 done
 
 # Autoconf <=2.59b set at_top_builddir instead of at_top_build_prefix:
-: ${at_top_build_prefix=$at_top_builddir}
+: "${at_top_build_prefix=$at_top_builddir}"
 
 # Perform any assignments requested during argument parsing.
 eval "$at_debug_args"
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 15dd80d1..6b1c1ead 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -1617,7 +1617,7 @@ m4_define([_AS_LITERAL_HEREDOC_IF_NO], [$2])
 # which name is inspired by PREFIX (should be 2-4 chars max).
 m4_define([AS_TMPDIR],
 [# Create a (secure) tmp directory for tmp files.
-m4_if([$2], [], [: ${TMPDIR=/tmp}])
+m4_if([$2], [], [: "${TMPDIR=/tmp}"])
 {
   as_tmp=`(umask 077 && mktemp -d "m4_default([$2],
     [$TMPDIR])/$1XXXXXX") 2>/dev/null` &&
diff --git a/tests/autotest.at b/tests/autotest.at
index 04524a50..811417bc 100644
--- a/tests/autotest.at
+++ b/tests/autotest.at
@@ -1502,7 +1502,7 @@ for signal in 2 15; do
   # AT_CHECK([[grep '[iI]nterrupt[	 ]' stderr]], [1])
 
   # Ditto with `make' in the loop.
-  : ${MAKE=make}
+  : "${MAKE=make}"
   unset MAKEFLAGS
   # Need to eliminate outer TESTSUITEFLAGS here.
   # Need to normalize exit status here: some make implementations
diff --git a/tests/c.at b/tests/c.at
index 8e772336..0e09798a 100644
--- a/tests/c.at
+++ b/tests/c.at
@@ -368,7 +368,7 @@ int main ()
 }
 ]])
 
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([env ACLOCAL=true autoreconf -vi], [], [ignore], [ignore])
 AT_CHECK([./configure $configure_options], [], [ignore], [ignore])
 AT_CHECK([$MAKE], [], [ignore], [ignore])
@@ -411,7 +411,7 @@ AT_DATA([foo.cpp],
 }
 ]])
 
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([env ACLOCAL=true autoreconf -vi], [], [ignore], [ignore])
 AT_CHECK([./configure $configure_options], [], [ignore], [ignore])
 AT_CHECK([$MAKE], [], [ignore], [ignore])
diff --git a/tests/foreign.at b/tests/foreign.at
index b223d206..08cb8b19 100644
--- a/tests/foreign.at
+++ b/tests/foreign.at
@@ -122,7 +122,7 @@ copy-shtool:
 : >file1
 : >file2
 chmod +x file1
-: ${MAKE=make}
+: "${MAKE=make}"
 mkdir build-aux inst
 instdir=`pwd`/inst
 AT_CHECK_AUTOCONF
diff --git a/tests/fortran.at b/tests/fortran.at
index c723748f..4397e354 100644
--- a/tests/fortran.at
+++ b/tests/fortran.at
@@ -107,7 +107,7 @@ AT_DATA([foo.f],
       end
 ]])
 
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([env ACLOCAL=true autoreconf -vi], [], [ignore], [ignore])
 AT_CHECK_CONFIGURE
 AT_CHECK([$MAKE], [], [ignore], [ignore])
@@ -147,7 +147,7 @@ AT_DATA([foo.f],
       end
 ]])
 
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([env ACLOCAL=true autoreconf -vi], [], [ignore], [ignore])
 AT_CHECK_CONFIGURE
 AT_CHECK([$MAKE], [], [ignore], [ignore])
@@ -240,7 +240,7 @@ int main(int argc, char *argv[])
 AT_CHECK_AUTOCONF
 AT_CHECK_AUTOHEADER
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram])
 
@@ -321,7 +321,7 @@ int main (int argc, char *argv[])
 AT_CHECK_AUTOCONF
 AT_CHECK_AUTOHEADER
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram])
 
@@ -400,7 +400,7 @@ int F77_MAIN (int argc, char *argv[])
 AT_CHECK_AUTOCONF
 AT_CHECK_AUTOHEADER
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram], [], [output from C main
 dnl  some output from Fortran sources
@@ -482,7 +482,7 @@ int FC_MAIN (int argc, char *argv[])
 AT_CHECK_AUTOCONF
 AT_CHECK_AUTOHEADER
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram], [], [output from C main
 dnl  some output from Fortran sources
@@ -559,7 +559,7 @@ int main(int argc, char *argv[])
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram])
 
@@ -633,7 +633,7 @@ int main(int argc, char *argv[])
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./cprogram])
 AT_CLEANUP
@@ -718,7 +718,7 @@ end
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 
 AT_CLEANUP
@@ -754,7 +754,7 @@ end
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./prog])
 
@@ -792,7 +792,7 @@ end
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./prog])
 
@@ -830,7 +830,7 @@ C      fixed-form style comment
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./prog])
 
@@ -869,7 +869,7 @@ C      fixed-form style comment
 
 AT_CHECK_AUTOCONF
 AT_CHECK_CONFIGURE
-: ${MAKE=make}
+: "${MAKE=make}"
 AT_CHECK([$MAKE], [], [ignore], [ignore])
 dnl AT_CHECK([./prog])
 
@@ -933,7 +933,7 @@ EOF
 
     AT_CHECK_AUTOCONF
     AT_CHECK_CONFIGURE
-    : ${MAKE=make}
+    : "${MAKE=make}"
     AT_CHECK([$MAKE], [], [ignore], [ignore])
     dnl AT_CHECK([./prog])
     AT_CHECK([$MAKE clean], [], [ignore], [ignore])
diff --git a/tests/tools.at b/tests/tools.at
index 167d68a8..20e90379 100644
--- a/tests/tools.at
+++ b/tests/tools.at
@@ -1160,7 +1160,7 @@ AT_CLEANUP
 # -----------------------------
 
 AT_SETUP([autom4te preselections])
-: ${sleep='sleep 1'}	# Command to force different time stamps.
+: "${sleep='sleep 1'}"	# Command to force different time stamps.
 # If this test should run on FAT file systems and older w32,
 # then setting $sleep correctly needs to be revisited.
 
diff --git a/tests/torture.at b/tests/torture.at
index 97cb5c6c..a8a2aa15 100644
--- a/tests/torture.at
+++ b/tests/torture.at
@@ -1213,7 +1213,7 @@ all: f f1 f2
 
 AT_CHECK_AUTOCONF
 
-: ${MAKE=make}
+: "${MAKE=make}"
 
 # In place.
 AT_CHECK([./configure $configure_options], [], [ignore])