'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH incr n "" Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
incr \- Increment the value of a variable
.SH SYNOPSIS
\fBincr \fIvarName \fR?\fIincrement\fR?
.BE
.SH DESCRIPTION
.PP
Increments the value stored in the variable whose name is \fIvarName\fR.
The value of the variable must be an integer.
If \fIincrement\fR is supplied then its value (which must be an
integer) is added to the value of variable \fIvarName\fR;  otherwise
1 is added to \fIvarName\fR.
The new value is stored as a decimal string in variable \fIvarName\fR
and also returned as result.
.PP
Starting with the Tcl 8.5 release, the variable \fIvarName\fR passed
to \fBincr\fR may be unset, and in that case, it will be set to
the value \fIincrement\fR or to the default increment value of \fB1\fR.
.SH EXAMPLES
.PP
Add one to the contents of the variable \fIx\fR:
.PP
.CS
\fBincr\fR x
.CE
.PP
Add 42 to the contents of the variable \fIx\fR:
.PP
.CS
\fBincr\fR x 42
.CE
.PP
Add the contents of the variable \fIy\fR to the contents of the
variable \fIx\fR:
.PP
.CS
\fBincr\fR x $y
.CE
.PP
Add nothing at all to the variable \fIx\fR (often useful for checking
whether an argument to a procedure is actually integral and generating
an error if it is not):
.PP
.CS
\fBincr\fR x 0
.CE
.SH "SEE ALSO"
expr(n), set(n)
.SH KEYWORDS
add, increment, variable, value
