What is the recommended way of concatenation of strings?
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- Look also answers at stackoverflow.com/questions/1430093/…B. Go– B. Go2019-06-19 22:52:43 +00:00Commented Jun 19, 2019 at 22:52
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5 Answers
Tcl does concatenation of strings as a fundamental operation; there's not really even syntax for it because you just write the strings next to each other (or the variable substitutions that produce them).
set combined $a$b If you're doing concatenation of a variable's contents with a literal string, it can be helpful to put braces around the variable name or the whole thing in double quotes. Or both:
set combined "$a${b}c d" Finally, if you're adding a string onto the end of a variable, use the append command; it's faster because it uses an intelligent memory management pattern behind the scenes.
append combined $e $f $g # Which is the same as this: set combined "$combined$e$f$g" 
2 Comments
Donal Fellows
Note that the first argument to
append is a variable name, just like the first arg to set.
ilkkachu
This isn't really right in that you can't write arbitrary strings back-to-back and get their concatenation. E.g.
"a""b" , or {foo}"bar" don't work. It's more true in awk, where something like $1 ":" $2 does work.Use append.
set result "The result is " append result "Earth 2, Mars 0" 
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If they are contained in variables, you can simply write "$a$b".
2 Comments
Narek
I am doing exactly in the way you have written with a small difference like ${a}${b}, but I worry that it is not a correct way to do, is it?
TrojanName
They are both right - you would use the ${a}${b} construction in the case where you are building a string and there may be an ambiguity about the variable name e.g. set url /admin/item-edit?item_name=${item_id}name
These days, you can concatenate two literal strings using the "string cat" command:
set newstring [string cat "string1" "string2"] 
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# using join set a {abcd} set b {efgh} set l [list $a $b] # a list set c [join $l ] # space sep (default) set d [join $l {}] # no sep puts $c abcd efgh puts $d abcdefgh 