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POPERL: Using REGEX to match a string without the first token repeated in the string. (ABC, not AAA ABC)
 

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  1. POPERL: Using REGEX to match a string without the first token repeated in the string. (ABC, not AAA ABC)
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    <p>I am relatively new to perl and I apologize in advance if this question is simple and I am missing something completely obvious, however, I've been looking around for the answer for a couple of days now and can't find a solution. </p> <p>I am trying to use a regular expression to match the FIRST instance where A is followed by C without another A in between A and C. Note that in this text string there are other instances following the first A.C combination that could also fit the A.C, (specifically note the ADC) Here is the text:</p> <pre><code>$text = "AAA ABC ADE AFG ADC AHI AJK AIZ XXB NBV"; </code></pre> <p>I first tried:</p> <pre><code>@finds1=$TEXT=~m/(A.*?C)/; $result = $finds1[0]; print "result = $result\n"; </code></pre> <p>This prints the following: </p> <pre><code>result = AAA ABC </code></pre> <p>When what I want is just:</p> <pre><code>result = ABC </code></pre> <p>Note that I am trying to create a regular expression that could be used where B could be any string of characters. For example ADC, AFGHJKC, AYUIOKJHGTC. </p> <p>I next tried to use a look-forward combined with an if then else statement. Here is the code:</p> <pre><code>@finds1=$TEXT=~m/(A(?(?!.*?A.*?C).*?C|Z{100}))/; $result = $finds1[0]; print "result = $result\n"; </code></pre> <p>The first part of the REGEX, (A, tells perl to find an occurrence of A. Once found, perl then processes the if then else statement where the conditional statement is that there are no instances of .<em>?A.</em>?A following the A, if none are found then perl looks for .*?C, if at least one is found, then it searches for 100 instances of Z. (my way of getting Perl to move on since neither in this text nor in the text I'm trying to parse are there 100 Zs.) </p> <p>This returns: </p> <pre><code>result = ADC </code></pre> <p>I have considered using a positive look-behind after identifying C for the first time. However, like I mentioned above, The number of characters between the first A.C combination without an A in between them is variable. As far as I know PERL can't do variable-length look-behinds. </p> <p>Any help or direction you could provide would be GREATLY appreciated!!</p> <p>Thanks in advance!</p>
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    1. COAm I wrong in my interpretation that /A[b-zB-Z]*?C/ would fit the bill?
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    2. COYou are correct. It does work on this text. Thanks for your response. How would you modify it to accommodate spaces between the A and the C (e.g. $text = "AAA A B C ADE AFG ADC AHI AJK AIZ XXB NBV";
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    3. COHere, I'll expand upon it so that it's answer-worthy, and answer your question there as well.
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