Tcl string concatenation

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—

Two string variables can easily be concatenated as follows:
```
set alpha "Hel"
set beta "lo"
puts stdout $alpha$beta
```
This gives:
```
Hello
```

Another way is to use append:

set alphabeta "Hel"
append alphabeta "lo"
puts stdout $alpha$beta

This gives:

Hello

However, when mixing a string variable and a literal string, the result is not what would be expected:
```
set alpha "Hel"
puts stdout $alpha"Hel"
```
This gives:
```
Hel"lo"
```

It is important to note that the concat tcl function applies on lists. It is possible to concat some strings by using a list but this is not the good way:
```
set alphabeta [concat "Hel" "lo"]
puts stdout $alphabeta
```
This gives a list of two members, displayed with a space between them:
```
Hel lo
```
A list can be merged to give a string (here without spaces between members) as follows:
```
set alphabeta [join [concat "Hel" "lo"] ""
puts stdout $alphabeta
```
This gives:
```
Hello
```
However this is not efficient.

Finally, the simplest way is by using curly braces to separate the variable name:
```
set alpha "Hel"
set alphabeta ${alpha}lo
puts stdout $alphabeta
```
This gives:
```
Hello
```

Conclusion:

With append:

set alphabeta "Hel"
append alphabeta "lo"

With curly braces:

set alpha "Hel"
set alphabeta ${alpha}lo

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This page is part of the Tcl/Tk page of the Airplug documentation.
Back to the Tcl/Tk page / Back to Airplug documentation page.