Regex to match even hex numbers in Tcl?

Question

Is there away to write a Tcl regex to verify that a string is a hex number that is even?

A hex number is easy. Checking eveness is still possible (actually, still easy) because the last digit determines that - but in general, you should read http://stackoverflow.com/questions/4098086/to-use-or-not-to-use-regular-expressions/4098123#4098123 and heed its wisdom. — , Mar 31 '11 at 18:54

score 4 · Accepted Answer · edited Mar 31 '11 at 21:07

4

This tcl code will do the work:

if {[regexp -linestop -nocase {^[\da-f]*[02468ace]$} $input]} {
    # Success
} else {
    # Fail
}

Note that a, c and e are also even numbers and that you need -nocase to match a-f as well as A-F.

edited Mar 31 '11 at 21:07

glenn jackman

answered Mar 31 '11 at 19:02

Staffan Nöteberg

I added braces around the if condition to delay evaluation – glenn jackman Mar 31 '11 at 21:07
You probably don't need `-linestop`; the default “match the whole string” behavior is suitable for this sort of task. – Donal Fellows Apr 02 '11 at 08:06

score 4 · Answer 2 · answered Mar 31 '11 at 21:05

4

Does it need to be a regex?

proc is_even {n} {expr {($n & 1) == 0}}

if {[is_even 0xdeadbeef]} {puts even} else {puts odd}

answered Mar 31 '11 at 21:05

glenn jackman

2 Answers2