append Append values to variable
binary Insert and extract fields from binary strings
format printf() -style string formatting
regexp Regular expression pattern matching
regsub Regular expression string substution
scan sscanf() -style string formatting
string compare Lexical(词汇的) string comparison
string first Search for first occurrence of substring
string index Return character from string
string last Search for last occurance of substring
string length Return number of characters in string
string range Return range of characters in string
string tolower Covert to lowercase
string toupper Covert to uppercase
string trim Remove leading and trailing characters
string trimleft Remove leading characters
string trimright Remove trailing characters
string wordend Return end position of word in string
string wordstart Return start position of word in string
subst Blackslash,command,variable substitutions
原文：https://www.cnblogs.com/lelin/p/11281540.html