Hi everybody,
We noticed that the LPI Essentials V1.5 still have the following item:
in: 3.2 Searching and Extracting Data from Files
under: Key Knowledge Areas
Basic Regular Expressions using ., [ ], *, and ?
The problem is that '?' is not part of the Basic Regular Expressions
at all, so this requirement is a contradiction in terms.
The '?'is a part of the Extended Regular Expressions, but i.m.h.o.
things get too complicated for a beginners level if we have to
touch on the difference between thasee two.
Just a few examples, exercising this '?' meaning: "zero or
one of the preceding", and using curly brackets to obtain
a similar "range from.. to..." effect:
BRE: echo papa | grep 'papa?'
-> no output
ERE: echo papa | grep -E 'papa?'
-> output: papa
BRE: echo papa | grep 'papa\{0,1\}'
-> output papa
ERE: echo papa | grep -E 'papa{0,1}'
-> output papa
My suggestion: drop the '?' (and don't introduce the curly brackets).
However: I dearly miss the ^ and $ anchors, and in my opinion
the [^....] is indispensable as well.
Hendrik-Jan
--
Hendrik-Jan Thomassen <[email protected]>
AT Computing
Linux/UNIXperts,
opleiders & oplossers Tel +31 24 352 72 82
Kerkenbos 1238 Tel cursussecretariaat: +31 24 352 72 72
6546 BE Nijmegen Fax +31 24 352 72 92
[email protected] www.atcomputing.nl
'If you think education is expensive, try ignorance.'
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