Using a null value as part of a regular expression.

[Thomas Fortino]

Hello Fellow Clovertechers,

   

  I’m trying to use an use the following regular expression in a tclproc to as part of if condition to continue a message. The values are IN and null {}. The regexp recognizes the IN but does not recognize the {} null.

The regexp is below –

if [regexp — IN|{} $vip] {

I have tried escaping the {} using { } and “{}” but neither worked. I continue looking in the Brent Welch book but any help would be appreciated.

AIX 5.1

Platform V rev5.2

Topic

[Charlie Bursell]

Tcl is iterpreting the {} as an empty string.  Pass the regular express to the parser with braces and Tcl will leave it alone.

Try this:

regexp — {IN|{}} $vip

Works for me

[Chris Williams]

regexp — {IN|^$} $vip

Returns 1 for IN and null.

Returns 0 for other non-null values.

You need the curly braces surrounding the expression. The caret and dollar sign mark the beginning and end of a string (with nothing between them).

[Thomas Fortino]

Thanks Charlie and Chris both examples worked great.

[Chris Williams]

Thomas,

Be aware of how you are representing a null string in your testing. Both regexp expressions will give you matches. However,

^$ will match a null (empty) string.

00 will match a character that is a null.

{} will match a pair of curly brace characters.

[Charlie Bursell]

What Chris is saying is true.  I was under the assumption you want to match a literal pair of braces

[Thomas Fortino]

Thank, I used Chris’s code because I was looking for a null value. I tested the using both “IN” and a empty field in the data.

regexp — {IN|^$} $vip

[Author]

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