configure: avoid un-recommended command substitution form

The use of backticks to surround commands instead of "$(cmd)" is a
legacy of the oldest pre-POSIX shells. It is confusing, unreliable, and
hard to read. Its use is not recommended in new programs.

Link: http://mywiki.wooledge.org/BashFAQ/082
Signed-off-by: Eli Schwartz <eschwartz93@gmail.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/configure b/configure
index 488c5f880962aa546f840c77db53ee15a4f86f4c..158e76e187b20527dd123316be7650db473ba449 100755 (executable)
--- a/configure
+++ b/configure
@@ -250,8 +250,8 @@ check_elf()
        echo "HAVE_ELF:=y" >>$CONFIG
        echo "yes"
 
-       echo 'CFLAGS += -DHAVE_ELF' `${PKG_CONFIG} libelf --cflags` >> $CONFIG
-       echo 'LDLIBS += ' `${PKG_CONFIG} libelf --libs` >>$CONFIG
+       echo 'CFLAGS += -DHAVE_ELF' "$(${PKG_CONFIG} libelf --cflags)" >> $CONFIG
+       echo 'LDLIBS += ' "$(${PKG_CONFIG} libelf --libs)" >>$CONFIG
     else
        echo "no"
     fi
@@ -369,8 +369,8 @@ check_selinux()
                echo "HAVE_SELINUX:=y" >>$CONFIG
                echo "yes"
 
-               echo 'LDLIBS +=' `${PKG_CONFIG} --libs libselinux` >>$CONFIG
-               echo 'CFLAGS += -DHAVE_SELINUX' `${PKG_CONFIG} --cflags libselinux` >>$CONFIG
+               echo 'LDLIBS +=' "$(${PKG_CONFIG} --libs libselinux)" >>$CONFIG
+               echo 'CFLAGS += -DHAVE_SELINUX' "$(${PKG_CONFIG} --cflags libselinux)" >>$CONFIG
        else
                echo "no"
        fi
@@ -382,8 +382,8 @@ check_tirpc()
                echo "HAVE_RPC:=y" >>$CONFIG
                echo "yes"
 
-               echo 'LDLIBS +=' `${PKG_CONFIG} --libs libtirpc` >>$CONFIG
-               echo 'CFLAGS += -DHAVE_RPC' `${PKG_CONFIG} --cflags libtirpc` >>$CONFIG
+               echo 'LDLIBS +=' "$(${PKG_CONFIG} --libs libtirpc)" >>$CONFIG
+               echo 'CFLAGS += -DHAVE_RPC' "$(${PKG_CONFIG} --cflags libtirpc)" >>$CONFIG
        else
                echo "no"
        fi
@@ -395,8 +395,8 @@ check_mnl()
                echo "HAVE_MNL:=y" >>$CONFIG
                echo "yes"
 
-               echo 'CFLAGS += -DHAVE_LIBMNL' `${PKG_CONFIG} libmnl --cflags` >>$CONFIG
-               echo 'LDLIBS +=' `${PKG_CONFIG} libmnl --libs` >> $CONFIG
+               echo 'CFLAGS += -DHAVE_LIBMNL' "$(${PKG_CONFIG} libmnl --cflags)" >>$CONFIG
+               echo 'LDLIBS +=' "$(${PKG_CONFIG} libmnl --libs)" >> $CONFIG
        else
                echo "no"
        fi
@@ -436,8 +436,8 @@ EOF
        echo "no"
     else
        if ${PKG_CONFIG} libbsd --exists; then
-               echo 'CFLAGS += -DHAVE_LIBBSD' `${PKG_CONFIG} libbsd --cflags` >>$CONFIG
-               echo 'LDLIBS +=' `${PKG_CONFIG} libbsd --libs` >> $CONFIG
+               echo 'CFLAGS += -DHAVE_LIBBSD' "$(${PKG_CONFIG} libbsd --cflags)" >>$CONFIG
+               echo 'LDLIBS +=' "$(${PKG_CONFIG} libbsd --libs)" >> $CONFIG
                echo "no"
        else
                echo 'CFLAGS += -DNEED_STRLCPY' >>$CONFIG
@@ -453,8 +453,8 @@ check_cap()
                echo "HAVE_CAP:=y" >>$CONFIG
                echo "yes"
 
-               echo 'CFLAGS += -DHAVE_LIBCAP' `${PKG_CONFIG} libcap --cflags` >>$CONFIG
-               echo 'LDLIBS +=' `${PKG_CONFIG} libcap --libs` >> $CONFIG
+               echo 'CFLAGS += -DHAVE_LIBCAP' "$(${PKG_CONFIG} libcap --cflags)" >>$CONFIG
+               echo 'LDLIBS +=' "$(${PKG_CONFIG} libcap --libs)" >> $CONFIG
        else
                echo "no"
        fi