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terraform/website/docs/configuration/functions/tonumber.html.md

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lang/funcs: Type conversion functions It's not normally necessary to make explicit type conversions in Terraform because the language implicitly converts as necessary, but explicit conversions are useful in a few specialized cases: - When defining output values for a reusable module, it may be desirable to force a "cleaner" output type than would naturally arise from a computation, such as forcing a string containing digits into a number. - Our 0.12upgrade mechanism will use some of these to replace use of the undocumented, hidden type conversion functions in HIL, and force particular type interpretations in some tricky cases. - We've found that type conversion functions can be useful as _temporary_ workarounds for bugs in Terraform and in providers where implicit type conversion isn't working correctly or a type constraint isn't specified precisely enough for the automatic conversion behavior. These all follow the same convention of being named "to" followed by a short type name. Since we've had a long-standing convention of running all the words together in lowercase in function names, we stick to that here even though some of these names are quite strange, because these should be rarely-used functions anyway.
2019-01-17 18:11:48 +01:00
---
layout: "functions"
page_title: "tonumber - Functions - Configuration Language"
sidebar_current: "docs-funcs-conversion-tonumber"
description: |-
The tonumber function converts a value to a number.
---
# `tonumber` Function
website: Version notes: Add new -> old links to 0.12 language docs (function pages)
2019-01-17 01:33:57 +01:00
-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
earlier, see
[0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
lang/funcs: Type conversion functions It's not normally necessary to make explicit type conversions in Terraform because the language implicitly converts as necessary, but explicit conversions are useful in a few specialized cases: - When defining output values for a reusable module, it may be desirable to force a "cleaner" output type than would naturally arise from a computation, such as forcing a string containing digits into a number. - Our 0.12upgrade mechanism will use some of these to replace use of the undocumented, hidden type conversion functions in HIL, and force particular type interpretations in some tricky cases. - We've found that type conversion functions can be useful as _temporary_ workarounds for bugs in Terraform and in providers where implicit type conversion isn't working correctly or a type constraint isn't specified precisely enough for the automatic conversion behavior. These all follow the same convention of being named "to" followed by a short type name. Since we've had a long-standing convention of running all the words together in lowercase in function names, we stick to that here even though some of these names are quite strange, because these should be rarely-used functions anyway.
2019-01-17 18:11:48 +01:00
`tonumber` converts its argument to a number value.
Explicit type conversions are rarely necessary in Terraform because it will
convert types automatically where required. Use the explicit type conversion
functions only to normalize types returned in module outputs.
Only numbers and strings containing decimal representations of numbers can be
converted to number. All other values will produce an error.
## Examples
```
> tonumber(1)
1
> tonumber("1")
1
> tonumber("no")
Error: Invalid function argument
Invalid value for "v" parameter: cannot convert "no" to number: string must be
a decimal representation of a number.
```