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Regular Expression: detecting 2 or more consecutive spaces oddity

Sheppy

Hi,

For a particular script I have to check whether or not a string has two or more consecutive spaces between lower-case characters. Zero and one space are allowed, two or more not. I am using rexMatchp() to check. Please have a look at the following code+output:

rexMatchp("[a-z][ ]{2,}[a-z]" "test test")

nil

rexMatchp("[a-z][ ]{2,}[a-z]" "test  test")

nil

rexMatchp("[a-z][ ]{2,}[a-z]" "test   test")

nil

rexMatchp("[a-z][ ][ ]+[a-z]" "test test")

nil

rexMatchp("[a-z][ ][ ]+[a-z]" "test  test")

t

rexMatchp("[a-z][ ][ ]+[a-z]" "test   test")

t

The three last commands do exactly what I want. However, the first three do not work, although this is perfectly legal syntax for a regular expression. I found in the Virtuoso documentation that using {} to specify the number of occurrences is supported, but it clearly doesn't work in my example.

Am I doing something wrong?

With kind regards,

Sjoerd

Parents

  • Hi Sjoerd,

    Was a bit difficult to see the wood from the trees in all of this - but the key problem is the "-" character in the pattern. The trouble is that this is being interpreted as a "range" separator - in fact pcreCompile gives a warning to that respect.

    So if you do this:

    pattern = "[`\\-=;'./~!@$%^&*()_+{}|:\"<>?\\[\\]]"
    ;pattern = "\\S"
    testString = "`-=;'./~!@$%^&*()_+{}|:\"<>?[]"
    pat=pcreCompile(pattern)
    for( i 1 strlen( testString )
      printf( "%L - %L\n" substring( testString i 1 ) pcreExecute(pat substring( testString i 1 ) ) )
    )

    You'll see it works (notice the double backslash before the - in the expression - you can do the same in your main code of course). It's a double backslash, because SKILL also uses backslash to escape characters in strings, and backslash is an escape character in regular expressions, so to get an RE \ you need \\. I also answered the bonus question of how to add [] inside the [] - escape them (see the end of the pattern).

    Note you could also use \\S (see "man perlre" for info on Perl regular expressions) but maybe you want to exclude particular characters - you could use other complex ranges though maybe to make it simpler.

    In order to detect a non-carriage-return terminated line, I just added this to your code:

    printf("READ %L NEWLINE %L\n" nextLine pcreMatchp("\n" nextLine))

    The pcreMatchp would return nil for the last line in the file if it didn't have a carriage return (or rather newline) at the end.

    It wasn't entirely clear what the expected output of your program was, but hopefully the above will give enough pointers in the right direction.

    Regards,

    Andrew.

Reply

  • Hi Sjoerd,

    Was a bit difficult to see the wood from the trees in all of this - but the key problem is the "-" character in the pattern. The trouble is that this is being interpreted as a "range" separator - in fact pcreCompile gives a warning to that respect.

    So if you do this:

    pattern = "[`\\-=;'./~!@$%^&*()_+{}|:\"<>?\\[\\]]"
    ;pattern = "\\S"
    testString = "`-=;'./~!@$%^&*()_+{}|:\"<>?[]"
    pat=pcreCompile(pattern)
    for( i 1 strlen( testString )
      printf( "%L - %L\n" substring( testString i 1 ) pcreExecute(pat substring( testString i 1 ) ) )
    )

    You'll see it works (notice the double backslash before the - in the expression - you can do the same in your main code of course). It's a double backslash, because SKILL also uses backslash to escape characters in strings, and backslash is an escape character in regular expressions, so to get an RE \ you need \\. I also answered the bonus question of how to add [] inside the [] - escape them (see the end of the pattern).

    Note you could also use \\S (see "man perlre" for info on Perl regular expressions) but maybe you want to exclude particular characters - you could use other complex ranges though maybe to make it simpler.

    In order to detect a non-carriage-return terminated line, I just added this to your code:

    printf("READ %L NEWLINE %L\n" nextLine pcreMatchp("\n" nextLine))

    The pcreMatchp would return nil for the last line in the file if it didn't have a carriage return (or rather newline) at the end.

    It wasn't entirely clear what the expected output of your program was, but hopefully the above will give enough pointers in the right direction.

    Regards,

    Andrew.

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