How to use logical IF with string function in Microsoft flow?

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Posted on by Gaolai

I built a flow to abstract a GUID from email body when new emails come in. The email body could contain:

3932FB4C-0DF5-11E8-A5C3-7804C4623542

KeyStart***3932FB4C-0DF5-11E8-A5C3-7804C4623542***KeyEnd

I have built the following expression to extract the GUID

if(greater(indexof(body('Html_to_text'), '***KeyEnd'), 1),
substring(body('Html_to_text'), Add(indexof(body('Html_to_text'), 'KeyStart***'), 11), 36),
substring(body('Html_to_text'), 0, 36))

For the second case, it works. For the first case, it always returns "index out of range" in the substring. Does anyone know why?

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StevenCollier 20 on at

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Re: How to use logical IF with string function in Microsoft flow?

Thanks @v-xida-msft this fixed my si,milar issue, but is there somewhere I can vote to get the if statement to not require this workaround.
Gaolai 46 on at

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Re: How to use logical IF with string function in Microsoft flow?

Thanks for your reply. I actually found out where the problem came from, the If operation will evaluate both parameter 2 and 3 no matter if the parameter 1 is true or false.
v-xida-msft on at

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Re: How to use logical IF with string function in Microsoft flow?

Hi @Gaolai,

Could you please share a screenshot of your flow's configuration?

The issue is confirmed on my side, I think this issue is related to the second parameter within your if() function. But when I add the following formula within a separated "Compose" action, the "Compose" action works well when the email body contains 3932FB4C-0DF5-11E8-A5C3-7804C4623542:

substring(body('Html_to_text'),0,36)

I afraid that this is issue is related to the if() function. In addition, you could consider take a try with the the following workaround as an alternative way:

Add a "When a new email arrives" trigger.

Add a "Html to text" action, Content field set to Body dynamic content of the trigger.

Add a Condition, click "Edit in advanced mode", type the following formula:

@greater(indexof(body('Html_to_text'), '***KeyEnd'), 1)

Within "If/yes" branch of Condition, add a "Compose" action, Inputs set to following formula:

substring(body('Html_to_text'),add(indexof(body('Html_to_text'),'KeyStart***'),11),36)

Within "If/no" branch of Condition, add a "Compose 2" action, Inputs set to following formula:

substring(body('Html_to_text'),0,36)

Image reference:

The flow works successfully as below:Best regards,

Kris