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Grouping with quotation marks
Words within double quotes are grouped into a single arguement:
set foo "hello, world" -> hello, world
whereas:
set foo hello world -> wrong # args: should be "set varName ?newValue?"
Grouping words within double quotes allows substitutions to occur within the quotations.
puts "The current stock value is $varName"
causes the current value of varName to be substituted for $varName, and then the entire string is printed to the output device.
In general, the backslash (\) disables substitution for the single character immediately following the backslash. Any character immediately following the backslash will stand without substitution.
However, there are specific "Backslash Sequence" strings which are replaced by specific values during the substitution phase. The following backslash strings will be substituted as shown below.
String Output Hex Value \a Audible Bell 0x07 \b Backspace 0x08 \f Form Feed (clear screen) 0x0c \n New Line 0x0a \r Carriage Return 0x0d \t Tab 0x09 \v Vertical Tab 0x0b \0dd Octal Value d is a number from 1-7 \xhh Hex Value h is a hex digit 0-9,A-F,a-f
The final exception is the backslash at the end of a line of text. This causes the interpreter to ignore the newline, and treat the text as a single line of text. The interpreter will insert a blank space at the location of the ending backslash.
Grouping with braces
Grouping words within braces disables substitution within the grouped string. The string is passed to a command exactly as written.
Grouping with square brackets
When words are grouped with square brackets, the first word is interpreted as the name of a command, and the following words are treated as that command's arguments. The results of the command is substituted for the whole group.
set foo [sin $angle]
causes the value in variable angle to be passed to the command 'sin'. The result of the sin command is then stored in variable foo.
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