Check if environment variable is set in configure script? - environment-variables

Question

I'm trying to test if ANDROID_NDK_ROOT is set in an Autoconf script. The relevant stanza is shown below. According to How can I check an environment variable? on the Autoconf mailing list, I can use:
if test "${var+set}" = set; then
echo "variable \$var is set to: $var"
fi
The variable is not set, but my AC_MSG_ERROR is not being executed.
$ printenv | grep ANDROID_NDK_ROOT
$
Instead, the test is producing the following error:
./configure: line 20616: syntax error near unexpected token `('
./configure: line 20616: ` $as_echo_n "(cached) " >&6'
(There's another reply in the thread but it seems to be just a comment and does not answer the question).
How do I test if an environmental variable is set in Autoconf?
Here is the stanza I am trying to execute in configure.ac:
# if test "$IS_ANDROID_OS" != "0"; then
if true; then
if test "${ANDROID_NDK_ROOT+set}" != set; then
AC_MSG_ERROR([ANDROID_NDK_ROOT is not set. Please set ANDROID_NDK_ROOT])
fi
THIS_FILE="$ANDROID_NDK_ROOT/sources/android/cpufeatures/cpu-features.h"
AC_CHECK_FILE([$THIS_FILE],
[cp "$THIS_FILE" "$ac_srcdir"],
AC_MSG_RESULT([cpu-features.h does not exist in ANDROID_NDK_ROOT, skipping])
)
THIS_FILE="$ANDROID_NDK_ROOT/sources/android/cpufeatures/cpu-features.c"
AC_CHECK_FILE([$THIS_FILE],
[cp "$THIS_FILE" "$ac_srcdir"],
AC_MSG_RESULT([cpu-features.c does not exist in ANDROID_NDK_ROOT, skipping])
)
fi
Here is the chunk of configure from cat -n:
20610
20611 THIS_FILE="$ANDROID_NDK_ROOT/sources/android/cpufeatures/cpu-features.c"
20612 as_ac_File=`$as_echo "ac_cv_file_$THIS_FILE" | $as_tr_sh`
20613 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $THIS_FILE" >&5
20614 $as_echo_n "checking for $THIS_FILE... " >&6; }
20615 if eval \${$as_ac_File+:} false; then :
20616 $as_echo_n "(cached) " >&6
20617 else
20618 test "$cross_compiling" = yes &&
20619 as_fn_error $? "cannot check for file existence when cross compiling""$LINENO" 5
20620 if test -r "$THIS_FILE"; then
20621 eval "$as_ac_File=yes"
20622 else
20623 eval "$as_ac_File=no"
20624 fi

Answer 1

I came across this old question and figured I'd share a solution I ended up using when I needed to check multiple variables were set (in this sanitized example, VAR1 thru VAR4):
m4_foreach_w([my_var],[VAR1 VAR2 VAR3 VAR4],[
AS_VAR_IF(myvar, [], AC_MSG_ERROR([Missing required variable: myvar!]))
AC_SUBST(myvar)dnl Export variable to Makefile as well
AC_ARG_VAR(myvar, [])dnl if this variable changes, re-run configuration
])

Answer 2

There's nothing wrong with your shell syntax for testing whether a variable is set, and it works fine with Autoconf.
The problem appears to arise from failing to quote the third arguments to the AC_CHECK_FILE() macros. You should always quote (with square brackets) each argument to each macro, especially when that argument is or contains a macro call itself. I can reproduce a syntax error in configure by wrapping the example code you provided between an AC_INIT and an AC_OUTPUT, but it goes away with proper quoting. Specifically, here:
THIS_FILE="$ANDROID_NDK_ROOT/sources/android/cpufeatures/cpu-features.h"
AC_CHECK_FILE([$THIS_FILE],
[cp "$THIS_FILE" "$ac_srcdir"],
[AC_MSG_RESULT([cpu-features.h does not exist in ANDROID_NDK_ROOT, skipping])]
)
THIS_FILE="$ANDROID_NDK_ROOT/sources/android/cpufeatures/cpu-features.c"
AC_CHECK_FILE([$THIS_FILE],
[cp "$THIS_FILE" "$ac_srcdir"],
[AC_MSG_RESULT([cpu-features.c does not exist in ANDROID_NDK_ROOT, skipping])]
)
Failing to quote the argument results in it being expanded too many times, and the resulting output indeed is not syntactically valid shell code.