Re: [vox] Help with Regular Expression?

[Henry House <hajhouse@MAPShouseag.com>]

BTW, it is better to start a new thread if you are introducing a totally new
topic, rather than replying to something unrelated.

On Fri, Sep 28, 2001 at 11:24:37AM -0700, Richard S. Crawford wrote:
> How in the world would you go about putting a character at the beginning of 
> a string or the end if the character isn't there?
> 
> For example,
> 
>         Bob     becomes         ABobA
>         ABob    becomes         ABobA
>         BobA    becomes         ABobA
>         ABobA   becomes         ABobA

You want all the strings to begin and end with A, but not double the As if
the A is there already.

Let's say you are using Perl. One way is to look for a three-part string:

	/^(A)?(.*[^A])(A)?$/

You need the [^A] because regexps are greedy --- if you use .+ instead, you
will find that the string

	AfooA

matches as 1 = 'A', 2 = 'fooA', and 3 = '', because the second part of the
pattern has greedily matched the longest string it can get.

The replacement:

	/A$1A/

We just throw away substrings 1 and 3 because their values are unimportant;
I just used them to make the example easier to understand.

-- 
Henry House
OpenPGP key available from http://romana.hajhouse.org/hajhouse.asc

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