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Re: Suggest a command line syntax

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Victor Porton wrote:

> I am writing a program (in fact a Perl script), which should do
> replacement of strings in a file, like this:
> 
> AB->BC
> BC->AB
> YY->ZZ
> 
> Note that Sed and relatives fail to do this task: It would replace BC back
> with AB after replacing AB with BC, and this is not what I need.
> 
> What command line syntax to specify strings to be replaced and replacement
> strings for my command?
> 
> I need an advice about the syntax of command line.

The idea sounds simple enough (although I can see some difficulties in 
writing the code in a robust and predictable way), but I want to be sure 
that I understand you. If I have it right, the user identifies a number of 
pairs of strings - to take your example, the pairs would be { AB, BC }, { 
BC, AB }, and { YY, ZZ } - and the program then does the following:

1) for each pair:
     identify all instances of the left member, and note its start and end 
position.

This loop is done *first*.

2) for each pair:
    for each instance:
      replace the left member with the right member.

So, for example, if we have the string

ABNNABNNBCNNZZNNYY

and the pairs { AB, BC }, { BC, AB }, { YY, ZZ }
we proceed as follows:

Phase 1: split

AB
NN
AB
NN
BC
NNZZNN
YY

Phase 2: replace

BC
NN
BC
NN
AB
NNZZNN
ZZ

Phase 3 (possibly incorporated into Phase 2): splice

BCNNBCNNABNNZZNNZZ

The difficulty comes when you have overlapping search strings. You need to 
be very careful how you handle (and document) them.

Anyway, assuming that's the general idea, the command line syntax could be 
something like:



programname -<options> -pairs p1a p1b [p2a p2b [p3a p3b [...]]] filespec

Options would be, for example, case-insensitivity (-i) and the like. Then 
would come the pairs - the switch '-pairs' might be considered surplus to 
requirements, so feel free to ditch it - and finally there is the file 
specification (if you're on Unix, you can just let globbing happen).

Alternatively, if there are many pairs, you could put them in a tab-
separated file, one pair per line, and specify the filename - e.g.

programname -i -f=swappairs.tsv j*.txt

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

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Thread

Suggest a command line syntax Victor Porton <porton@narod.ru> - 2014-12-22 20:10 +0200
  Re: Suggest a command line syntax Richard Heathfield <invalid@see.sig.invalid> - 2014-12-22 18:42 +0000
    Re: Suggest a command line syntax Victor Porton <porton@narod.ru> - 2014-12-22 20:48 +0200
      Re: Suggest a command line syntax Richard Heathfield <invalid@see.sig.invalid> - 2014-12-22 19:44 +0000
  Re: Suggest a command line syntax Kaz Kylheku <kaz@kylheku.com> - 2014-12-22 20:09 +0000
  Re: Suggest a command line syntax Robert Wessel <robertwessel2@yahoo.com> - 2014-12-22 14:46 -0600
    Re: Suggest a command line syntax Kaz Kylheku <kaz@kylheku.com> - 2014-12-22 21:40 +0000

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