incr(n) Tcl Built-In Commands incr(n)

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# [NAME](#NAME)

incr - Increment the value of a variable

# [SYNOPSIS](#SYNOPSIS)

**incr varName** ?*increment*?

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# [DESCRIPTION](#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**. If *varName* indicate an element that does not exist of an array that has a default value set, the sum of the default value and the *increment* (or 1) will be stored in the array element.

# [EXAMPLES](#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](#SEE_ALSO)

[expr(n)](/man/os/tcl/expr.n), [set(n)](/man/os/tcl/set.n)

# [KEYWORDS](#KEYWORDS)

add, increment, variable, value

Tcl

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Document: incr(n) from tcl 9.1.0-r0 (Chainguard OS)
Source: https://downloads.sourceforge.net/project/tcl/Tcl/9.1.0/tcl9.1.0-src.tar.gz