Returns the charIndex 'th character of the string argument. A charIndex of 0 corresponds to the first character of the string. charIndex may be specified as follows:
If charIndex is less than 0 or greater than or equal to the length of the string then an empty string is returned.
AMG: TIP #176 [L1 ] adds two more more indexing modes: integer-integer and integer+integer. These are certainly convenient. However, due to the fundamental need for concatenation and reparsing in any practical application, they are also slightly slower than just using [expr] to do the math. (Remember to always brace your expr-essions!)
There's also another mode which may be occasionally useful: end+integer. This comes in handy when the integer in question is already negative.
Returns for index an integer, the charIndex'th character in string. If index is end, the last character in string, and if index is end-integer, the last character minus the specified offset. (From the Tcl/Tk Reference Guide)
For example,
string index abcde 3
returns "d" . Notice that the index is zero based - the first character is index 0.
string index abcde 10
returns "" . There is no 10th character. No error is returned here.