Attempting to set two variables values according to the user input in a third variable. I am trying to use a switch statement but I am not sure if it is actually possible.
switch $sample_type_input {
CORE { set sample_type 1 \
set cutting ""}
SWC { set sample_type 2 \
set cutting ""}
CUTT { set sample_type 3 \
set cutting "CUTT" }
}
I keep getting a 'wrong # args: should be "set varName ?newBalue?"` error.
The backslash at the end of the line acts as a line continuation, concatenating this line and the next line into a single logical line of code. This is necessary in a case where one has to break up a command invocation into two or more lines, because of the parsing rules:
set foo
bar
is interpreted as two command invocations: set foo and bar.
set foo \
bar
is a single command invocation: set foo bar.
Note that the backslash must be the very last character before the newline: e.g. a space between the backslash and the newline simply makes the invocation end with a regular space and a quoted space:
# there is a space after the backslash here
set foo \
puts "{$foo}"
# => { }
If your command invocation includes an argument in braces, it's typically quite all right to break it up into several lines without a backslash, since all whitespace including newlines is quoted by the braces anyway:
set foo {
bar
baz
}
And indeed if the argument within braces is a script containing more than one command invocation, you need to break it up into lines (or insert semicolons), since newlines are significant as command line separators. Therefore this fails:
if {true} {set foo bar \
set baz quz}
as it concatenates two command invocations into the single code line set foo bar set baz quz, providing the set command with five arguments when it expects one or two. The correct way is to write it as
if {true} {set foo bar ; set baz quz}
or
if {true} {set foo bar
set baz quz}
letting the semicolon or newline separate the command invocations in the script argument. Stylistic convention is to add additional newlines at the beginning and end of a multi-line script argument, like this:
if {true} {
set foo bar
set baz quz
}
This is similar to C brace styles, but not quite the same thing. One common beginner mistake is to try to use some other C bracing convention such as
if {true}
{
set foo bar
set baz quz
}
which won't work since it introduces a codeline-separating newline between the first and second arguments to if. If you can't live without this bracing convention, you need to add a line continuation:
if {true} \
{
set foo bar
set baz quz
}
Documentation: if, puts, set, Summary of Tcl language syntax
(Note: the 'Hoodiecrow' mentioned in the comments is me, I used that nick earlier.)
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