How to Use Expressions in Power Automate

Introduction

Power Automate expressions are formulas used in Microsoft Power Automate flows to manipulate data, apply logic, and control automation behavior dynamically.

They allow you to build smarter, more flexible automation flows by working with:

Text (strings)
Numbers
Dates and times
Arrays
Objects
Logical conditions

Why Expressions Matter

Expressions make your flows dynamic and intelligent. For example:

Automatically format dates in emails
Check if a field is empty before proceeding
Combine multiple values into a single string
Calculate due dates
Extract part of a filename
Handle null values safely

Without expressions, flows would be limited to simple, static automation.

Where Expressions Are Used

In Power Automate, expressions can be added in:

Condition actions
Compose actions
Initialize/Set Variable
Dynamic content fields
Filter array
Apply to each
Email subjects, file names, approval text, etc.

They are written using a function-style syntax like:

functionName(parameter1, parameter2)

Example:

concat('Hello ', triggerBody()?['FirstName'])

How Expressions Work

Expressions:

Are case-sensitive
Use parentheses ()
Accept values, variables, or other expressions as parameters
Can be nested inside each other

Example of nesting:

if(equals(length('Power'),5),'Correct','Incorrect')

In short, expressions are the logic engine behind smart automation in Power Automate.

🔤 String Functions

Expression	Description	Example
`concat(a, b, ...)`	Combine multiple strings	`concat('Flow','-','CheatSheet')` → `"Flow-CheatSheet"`
`substring(text, start, length)`	Return part of a string	`substring('PowerAutomate',0,5)` → `"Power"`
`length(text)`	Number of characters	`length('Functions')` → `9`
`split(text, delim)`	Split string into array	`split('A,B,C',',')` → `['A','B','C']`
`toLower(text)`	Convert to lowercase	`toLower('Hello')` → `"hello"`
`trim(text)`	Remove leading/trailing spaces	`trim(' ABC ')` → `"ABC"`
`replace(text, old, new)`	Replace substring	`replace('one two',' ','-')` → `"one-two"`
`indexOf(text, value)`	First position of value	`indexOf('abcde','c')` → `2`
`lastIndexOf(text, value)`	Last position of value	`lastIndexOf('abcabc','c')` → `5`
`startsWith(text, value)`	Check prefix	`startsWith('Hello','He')` → `true`

📦 Collection / Array Functions

Expression	Description	Example
`join(array, delim)`	Join array elements	`join(['a','b','c'],'-')` → `"a-b-c"`
`first(array)`	First element	`first(['One','Two'])` → `"One"`
`last(array)`	Last element	`last(['One','Two'])` → `"Two"`
`union(a,b)`	Combine arrays (unique values)	`union(array1,array2)`
`intersection(a,b)`	Common elements	`intersection(array1,array2)`
`contains(array,item)`	Check if array contains item	`contains(['a','b'],'b')` → `true`
`length(array)`	Count items	`length(['a','b','c'])` → `3`

🔀 Logical & Conditional Functions

Expression	Description	Example
`if(cond, valT, valF)`	Conditional logic	`if(equals(1,1),'match','no match')` → `"match"`
`equals(a,b)`	Equality check	`equals(2,2)` → `true`
`greater(a,b)`	Greater than	`greater(5,3)` → `true`
`less(a,b)`	Less than	`less(2,4)` → `true`
`and(a,b,...)`	Logical AND	`and(true,false)` → `false`
`or(a,b,...)`	Logical OR	`or(true,false)` → `true`
`not(value)`	Logical NOT	`not(true)` → `false`
`empty(value)`	Check if empty	`empty('')` → `true`
`coalesce(a,b,...)`	First non-null value	`coalesce(null,'default')` → `"default"`

📅 Date & Time Functions

Expression	Description	Example
`utcNow()`	Current UTC date/time	`utcNow()`
`addDays(date,n)`	Add days	`addDays('2025-10-01',2)` → `"2025-10-03"`
`addHours(date,n)`	Add hours	`addHours('2025-10-26T10:00:00Z',3)`
`formatDateTime(date,fmt)`	Format date	`formatDateTime('2025-10-26','yyyy-MM-dd')`
`dayOfWeek(date)`	Day index (0=Sunday)	`dayOfWeek('2025-10-26')` → `0`

Conclusion

Expressions in Power Automate allow you to manipulate data, perform calculations, and control logic dynamically, making workflows more flexible and efficient. They are essential for transforming inputs and automating complex tasks without manual intervention.