OK, heres a weird one I came across.

I have a list of chemical names; something like:

3 L-homoserine
1 L-iditol

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As is the way with chemical names they have lots of synonyms and so I am replacing these with regular expressions. My problem arises because there may be an arbitrary numerator in front of the chemical name (as they came from a formula)... this needs to be preserved as the formulas will be rebuilt.

The synonym for L-iditol is L-Iditol (just a case change) so this is fine being replaced by:

s/(\d+ *)L\-iditol/\1L\-Iditol/

Simple and works... however the synonym for L-homoserine is infact 2-Amino-4-hydroxybutyric acid.

So I write the regex:

s/(\d+ *)L\-homoserine/\12\-Amino\-4\-hydroxybutyric\ acid/

When applied to L-homoserine I get a blank line then '-Amino-4-hydroxybutyric acid' (note the missing 2). Note that in the regular expression the replacement string begins \12 . The \1 bit includes the numerator (3 in the above example) but the 2 is actually part of the new string. When combined they don't work like this. I consulted by table of ascii values and find that \012 is infact the code for newline...

Has anyone had this problem before? How can I force \12 to behave as I want it rather than producing a new line?

Looking forward to resolving this strange one.

Arun

In reply to Regular expressions Containing Octal values? by arunhorne

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