All Those Other String Functions Are Handy, Too
There are numerous other string manipulation functions that can be used when working with patterns. For example, in Chapter 3 (p. 77), I used "string trimright
" to remove all the newline characters from the end of a string.
Another function that is very handy is scan
. The scan
command interprets strings according to a format. scan
is analogous to the C language scanf
function. For the most part, scan
is less powerful than regexp
, but occasionally the built-in capabilities of scan
provide exactly the right tool. For example, a regular expression to match a C-style real number is:
([0-9]+.?[0-9]*|[0-9]*.[0-9]+)([eE][-+]?[0-9]+)?
And that is before adding the backslashes in front of "[
“, ".
" and "+
“! A much better alternative is to use Tcl’s scan
command. This can match real numbers, plus you can constrain it for precision. All you have to do is feed it a string containing a number. You can have expect
look for the end of the number (such as by seeing whitespace) and then call:
scan $expect_out(string,0) "%f" num
In this example, the number is stored in the variable num
. The %f
tells scan
to extract a real number. Chapter 2 (p. 46) has more information on scan
and other string manipulation commands.
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