TCL Syntax

Created: 2022-09-14T20:50:58-05:00

• A script is a string containing one or more commands.
• Commands are separated by semicolons and unescaped newlines.
• A backslash followed by a newline is an escaped newline. For the purposes of parsing that is treated as though a single space " " character had been read.
• Commands are comprised of one or more words which are any contiguous characters separated by whitespace.
• A word which begins with double quotes represents a string where all characters until the next unescaped double quote are treated as a single word.
• Argument expansion: if a word starts with {*} and a non whitespace character then argument expansion happens. Argument expansion removes the {*} characters and performs parsing and substitution as normal. The result of that parsing and substitution is then parsed as a list without further variable and word substitutions.
• Braces: if the first character of the word is a brace "{" then capture all characters until the closing brace "}". Braces nest so unescaped { within a block must be matched with unescaped }.
• Command substituion: if the first character of the word is a "[" then treat the characters after the [ as a recursive TCL interpretation. Run that script (up to the next unescaped "]".)
• Variable substitution: $foo, $foo(index), and ${foo) replaces the word with some value which has been looked up.
• Backslashes: backslashes inside of a word are replaced according to a substitution table.
• Comments: When a word begins with "#" then ignore until after the next newline.
• Order of substitution: evaluation is done left to right and characters are touched only once.
• Substitution does not affect the bounds of a word. If the substitution introduces whitespace then those whitespace are considered part of the word.