---
name: "incr"
section: "n"
platform: "linux"
package: "tcl"
version: "8.6.16-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/incr/n"
---

# incr(n)

Increment the value of a variable

```

```

## NAME

incr - Increment the value of a variable

## SYNOPSIS

**incr** *varName* ?*increment*?

```

```

## DESCRIPTION

Increments the value stored in the variable whose name is *varName*. The value of the variable must be an integer. If *increment* is supplied then its value (which must be an integer) is added to the value of variable *varName*;  otherwise 1 is added to *varName*. The new value is stored as a decimal string in variable *varName* and also returned as result.

Starting with the Tcl 8.5 release, the variable *varName* passed to **incr** may be unset, and in that case, it will be set to the value *increment* or to the default increment value of **1**.

## EXAMPLES

Add one to the contents of the variable *x*:

```
incr x
```

Add 42 to the contents of the variable *x*:

```
incr x 42
```

Add the contents of the variable *y* to the contents of the variable *x*:

```
incr x $y
```

Add nothing at all to the variable *x* (often useful for checking whether an argument to a procedure is actually integral and generating an error if it is not):

```
incr x 0
```

## SEE ALSO

[expr(n)](/expr/n.md), [set(n)](/set/n.md)

## KEYWORDS

add, increment, variable, value