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Bash if statement can be used with regular expression

if [[ "hello world" =~ "hello" ]] ## this is true
then
    echo "'hello world' has 'hello'"
fi

if [[ "hello" =~ "hello world" ]] ## this is false
then
    echo "'hello' has 'hello world'"
fi

if [[ "hello world" =~ e.* ]] ## this is true
then
    echo "'hello world' has 'e' followed by any character"
fi

Note that

 - the bracket should be double

 - use "=~", not "~="

 - use the regular expression without quotation mark

 - the lefthand-side should be a container

When you are using very large concatenated signals in Vivado simulation, it may cause elaborate step failure. You can release this problem with breaking into several smaller signals.

AR# 62969 says it may be fixed in 2015.1 version, however, it still exists in 2017.2 version

www.xilinx.com/support/answers/62969.html

When you get [Opt 31-67] Problem from running Vivado opt_design phase, you have to check all the related input/output pins. If one of your input/output pins is not connected, it can occur. And also, even if you connect all the input/output pins, it can occur with a non-driving output pin.