search and replace exact substring

Hello,

I am parsing a string to check for an exact phrase. If the exact phrase is found, then I want to replace the phrase with a new phrase. The problem is, sometimes the phrase will be part of anothe phrase. Example:

wish to change the phrase "eps" to "%eps"

str = 'steps = eps*100 + beta*steps*eps';

newStr = 'steps = %eps*100 + beta*steps*%eps';

I'm having trouble picking out the exact phrase; each parsing phrase that I've come up with always catches something undesired e.g. 'steps' => 'st%eps' etc.

I've tried things like: st1 = regexprep(str,'^\w*(?=eps)^\w*','%eps')

(where I think I'm saing, look around the phrase "eps", if there's no "word" in the regexp sense, then replace the phrase with "%eps", but I'm obviously not there yet.

TIA,

CDQ (R2011b)

Answer 1

[Azzi Abdelmalek]

str = 'steps = eps*100 + beta*steps*eps';
regexprep([' ' str ' '],'(?<=[^a-zA-Z])eps(?=[^a-zA-Z])','%eps')

[Notsure USA]

This appears to solve my problem; thank you Azzi. I had (probably still have) a fundamental misunderstanding of the lookahead/lookbehind operators.

Answer 2

[Image Analyst]

newString = strrep(oldString, ' eps', ' %eps');

[Notsure USA]

Thank you for your answer; this was my original solution but unfortunately it doesn't catch one of the eps (the last one):

>> str = 'steps = eps*100 + beta*steps*eps';

>> newString = strrep(str, ' eps', ' %eps')

newString =

steps = %eps*100 + beta*steps*eps

[Image Analyst]

You could do it in two lines of code instead of one:

newString = strrep(oldString, ' eps', ' %eps');
newString = strrep(newString, '*eps', '%eps');

Likewise in the event you have any other symbols. Sorry for not doing this in the first place - thought you'd know. I find this much easier, and more straightforward and intuitive than trying to compose/invent complicated regexp expressions, so that's why I suggested it. Looks like you're quite adept with regexp though and can understand things like ' (?<=[^a-zA-Z])eps(?=[^a-zA-Z]) ', and that's great, because not everybody can.