あなたが実行するidea.shから
# ---------------------------------------------------------------------
# Locate a JDK installation directory which will be used to run the IDE.
# Try (in order): IDEA_JDK, JDK_HOME, JAVA_HOME, "java" in PATH.
# ---------------------------------------------------------------------
if [ -n "$IDEA_JDK" -a -x "$IDEA_JDK/bin/java" ]; then
JDK="$IDEA_JDK"
elif [ -n "$JDK_HOME" -a -x "$JDK_HOME/bin/java" ]; then
JDK="$JDK_HOME"
elif [ -n "$JAVA_HOME" -a -x "$JAVA_HOME/bin/java" ]; then
JDK="$JAVA_HOME"
else
JAVA_BIN_PATH=`which java`
if [ -n "$JAVA_BIN_PATH" ]; then
if [ "$OS_TYPE" = "FreeBSD" ]; then
JAVA_LOCATION=`JAVAVM_DRYRUN=yes java | "$GREP" '^JAVA_HOME' | "$CUT" -c11-`
if [ -x "$JAVA_LOCATION/bin/java" ]; then
JDK="$JAVA_LOCATION"
fi
elif [ "$OS_TYPE" = "SunOS" ]; then
JAVA_LOCATION="/usr/jdk/latest"
if [ -x "$JAVA_LOCATION/bin/java" ]; then
JDK="$JAVA_LOCATION"
fi
elif [ "$OS_TYPE" = "Darwin" ]; then
JAVA_LOCATION=`/usr/libexec/java_home`
if [ -x "$JAVA_LOCATION/bin/java" ]; then
JDK="$JAVA_LOCATION"
fi
fi
if [ -z "$JDK" -a -x "$READLINK" ]; then
JAVA_LOCATION=`"$READLINK" -f "$JAVA_BIN_PATH"`
case "$JAVA_LOCATION" in
*/jre/bin/java)
JAVA_LOCATION=`echo "$JAVA_LOCATION" | xargs dirname | xargs dirname | xargs dirname` ;;
*)
JAVA_LOCATION=`echo "$JAVA_LOCATION" | xargs dirname | xargs dirname` ;;
esac
if [ -x "$JAVA_LOCATION/bin/java" ]; then
JDK="$JAVA_LOCATION"
fi
fi
fi
fi