Returns -1, 0, or 1, depending on whether string1 is lexicographically less than, equal to, or greater than string2. Options are -nocase or -length integer. (From the Tcl/Tk Reference Guide)

"Lexicographically less, equal, or greater" means in terms of ASCII values. The less the ASCII value, the less the character is lexicographically.

Basically it means: . < 0 < 1 < 2 < ... < 9 < A < B < ... < Z < a < b < ... < z

The command compares the strings character by character beginning at the left side (i.e. the first character) until it either finds a difference or the end of the shortest string.

For example:

   string compare "abc" "xyz"

would return a -1, because "a" is less than "z" in ASCII.

   string compare "abcd" "abc"

would return a 1 - the first string is 'greater' than the second because it is longer.

What about

   string compare "3" "10"

While one might be tempted to say "well, 3 is less than 10, so it will return a -1", the true answer is that the above returns a "1" - because lexicographically, 3 comes after 1. This is a reason NOT to use string compare if the arguments may both be numeric a nd you want to know when one is truly less than the other.

The -nocase option ignores the case of the two strings as they are compared.

The -length NUMBER compares only the first NUMBER of characters. Note that this value is one based.

In April, 2003, Jeff Hobbs says:

... string compare should be used sparingly when string equal or string length is an alternative. string equal can do an extra quick check on whether the strings are of equal size first (since we know their size) before any char-by-char comparison must be done.

For general benchmarks see Tcl benchmarks and look at the STR ones for string comparisons.

See also

• string