ColdFusion query of queries syntax honors underscore as a single-character wildcard, and escaping of literal underscores with square brackets:
LIKE '_abc' -- any 1 char then abc
LIKE '[_]abc' -- actual underscore char then abc
Lucee (5.1 tested) doesn't appear to honor the wildcard, or the escaped version to match a literal underscore. Behavior is the same with or without cfqueryparam.
Does Lucee have a single character wildcard for QoQ, and if so, how do you escape that character when you want to find that actual literal?
You can do this by escaping the underscore using the "at" character, e.g.
LIKE '#_#abc' escape '#'
Related
I am struggling with writing regex expression in Snowflake.
SELECT
'DEM7BZB01-123' AS SKU,
RLIKE('DEM7BZB01-123','^DEM.*\d\d$') AS regex
I would like to find all strings that starts with "DEM" and ends with two digits. Unfortunately the expression that I am using returns FALSE.
I was checking this expression in two regex generators and it worked.
In snowflake the backslash character \ is an escape character.
Reference: Escape Characters and Caveats
So you need to use 2 backslashes in a regex to express 1.
SELECT
'DEM7BZB01-123' AS SKU,
RLIKE('DEM7BZB01-123', '^DEM.*\\d\\d$') AS regex
Or you could write the regex pattern in such a way that the backslash isn't used.
For example, the pattern ^DEM.*[0-9]{2}$ matches the same as the pattern ^DEM.*\d\d$.
You need to escape your backslashes in your SQL before it can be parsed as a regex string. (sometimes it gets a bit silly with the number of backslashes needed)
Your example should look like this
RLIKE('DEM7BZB01-123','^DEM.*\\d\\d$') AS regex
RLIKE (which is an alias in Snowflake for the SQL Standard REGEXP_LIKE function) implicitly adds ^ and $ to your search pattern...
The function implicitly anchors a pattern at both ends (i.e. '' automatically becomes '^$', and 'ABC' automatically becomes '^ABC$').
so you can remove them, and that then allows you to use $$ quoting
In single-quoted string constants, you must escape the backslash character in the backslash-sequence. For example, to specify \d, use \d. For details, see Specifying Regular Expressions in Single-Quoted String Constants (in this topic).
You do not need to escape backslashes if you are delimiting the string with pairs of dollar signs ($$) (rather than single quotes).
so you can simply use the regex DEM.*\d\d to find all strings that starts with DEM and ends with two digits without extra escaping as follows
SELECT
'DEM7BZB01-123' AS SKU
, RLIKE('DEM7BZB01-123', $$DEM.*\d\d$$) AS regex
which gives
SKU |REGEX|
-------------+-----+
DEM7BZB01-123|true |
I've got a little problem with regex.
I got few strings in one file looking like this:
TEST.SYSCOP01.D%%ODATE
TEST.SYSCOP02.D%%ODATE
TEST.SYSCOP03.D%%ODATE
...
What I need is to define correct regex and change those string name for:
TEST.D%%ODATE.SYSCOP.#01
TEST.D%%ODATE.SYSCOP.#02
TEST.D%%ODATE.SYSCOP.#03
Actually, I got my regex:
r".SYSCOP[0-9]{2}.D%%ODATE" - for finding this in file
But how should look like the changing regex? I need to have the numbers from a string at the and of new string name.
.D%%ODATE.SYSCOP.# - this is just string, no regex and It didn't work
Any idea?
Find: (SYSCOP)(\d+)\.(D%%ODATE)
Replace: $3.$1.#$2 or \3.\1.#\2 for Python
Demo
You may use capturing groups with backreferences in the replacement part:
s = re.sub(r'(\.SYSCOP)([0-9]{2})(\.D%%ODATE)', r'\3\1.#\2', s)
See the regex demo
Each \X in the replacement pattern refers to the Nth parentheses in the pattern, thus, you may rearrange the match value as per your needs.
Note that . must be escaped to match a literal dot.
Please mind the raw string literal, the r prefix before the string literals helps you avoid excessive backslashes. '\3\1.#\2' is not the same as r'\3\1.#\2', you may print the string literals and see for yourself. In short, inside raw string literals, string escape sequences like \a, \f, \n or \r are not recognized, and the backslash is treated as a literal backslash, just the one that is used to build regex escape sequences (note that r'\n' and '\n' both match a newline since the first one is a regex escape sequence matching a newline and the second is a literal LF symbol.)
I'm trying to match a variable length string followed by the filetype suffix in an XML filename using a regex:
varrrrrriableLengthString.xml
Currently I'm using this regex with a greedy match, the second backslash is to escape the first, which is to escape the dot.
[A-Za-z0-9]+\\.[xX][mM][lL]
I've tested this on RegExr, and it matches with only one backslash. However my CPP parser requires the double backslash.
How can I properly escape the filename suffix?
You can also escape chars using the [] notation, in your case [.]. The main advantage is that there is no "one or two backslashes?" question anymore, and I find it more readable IMHO.
It just does not work with brackets, i.e. to escape a [ (or ]), you still have to use \[ (or \\[ for a string literal) and not [[].
Backslashes still have to be escaped using another backslash too.
Here is the example that confuses me:
select ' w' ~ '^\s\w$';
This results in "false", but seems like it should be true.
select ' w' ~ '^\\s\w*$';
This results in "true", but:
Why does \s need the extra backslash?
If it truly does, why does \w not need the extra backslash?
Thanks for any help!
I think you have tested it the wrong way because I'm getting the opposite results that you got.
select ' w' ~ '^\s\w$';
Is returning 1 in my case. Which actually makes sense because it is matching the space at the beginning of the text, followed by the letter at the end.
select ' w' ~ '^\\s\w*$';
Is returning 0 and it makes sense too. Here you're trying to match a backslash at the beginning of the text followed by an s and then, by any number of letters, numbers or underscores.
A piece of text that would match your second regex would be: '\sw'
Check the fiddle here.
The string constants are first parsed and interpreted as strings, including escaped characters. Escaping of unrecognized sequences is handled differently by different parsers, but generally, besides errors, the most common behavior is to ignore the backslash.
In the first example, the right-hand string constant is first being interpreted as '^sw$', where both \s and \w are not recognized string escape sequences.
In the second example the right hand constant is interpreted as '^\sw*$' where \\s escapes the \
After the strings are interpreted they are then applied as a regular expression, '^\sw*$' matching ' w' where '^sw$' does not.
Some languages use backslash as an escape character. Regexes do that, C-like languages do that, and some rare and odd dialects of SQL do that. PostgresSQL does it. PostgresSQL is translating the backslash escaping to arrive at a string value, and then feeding that string value to the regex parser, which AGAIN translates whatever backslashes survived the first translation -- if any. In your first regex, none did.
For example, in a string literal or a regex, \n doesn't mean a backslash followed by a lowercase n. It means a newline. Depending on the language, a backslash followed by a lowercase s will mean either just a lowercase s, or nothing. In PostgresSQL, an invalid escape sequence in a string literal translates as the escaped character: '\w' translates to 'w'. All the regex parser sees there is the w. By chance, you used the letter w in the string you're matching against. It's not matching that w in the lvalue because it's a word character; it's matching it because it's a lowercase w. Change it to lowercase x and it'll stop matching.
If you want to put a backslash in a string literal, you need to escape it with another backslash: '\\'. This is why \\s in your second regex worked. Add a second backslash to \w if you want to match any word character with that one.
This is a horrible pain. It's why JavaScript, Perl, and other languages have special conventions for regex literals like /\s\w/, and why C# programmers use the #"string literal" feature to disable backslash escaping in strings they intend to use as regexes.
I can only find negative lookbehind for this , something like (?<!\\).
But this won't compile in c++ and flex. It seems like both regex.h nor flex support this?
I am trying to implement a shell which has to get treat special char like >, < of | as normal argument string if preceded by backslash. In other word, only treat special char as special if not preceded by 0 or even number of '\'
So echo \\>a or echo abc>a should direct output to a
but echo \>a should print >a
What regular expression should I use?
I'm using flex and yacc to parse the input.
In a Flex rule file, you'd use \\ to match a single backslash '\' character. This is because the \ is used as an escape character in Flex.
BACKSLASH \\
LITERAL_BACKSLASH \\\\
LITERAL_LESSTHAN \\\\<
LITERAL_GREATERTHAN \\\\>
LITERAL_VERTICALBAR \\\\|
If I follow you correctly, in your case you want "\>" to be treated as literal '>' but "\\>" to be treated as literal '\' followed by special redirect. You don't need negative look behind or anything particularly special to accomplish this as you can build one rule that would accept both your regular argument characters and also the literal versions of your special characters.
For purposes of discussion, let's assume that your argument/parameter can contain any character but ' ', '\t', and the special forms of '>', '<', '|'. The rule for the argument would then be something like:
ARGUMENT ([^ \t\\><|]|\\\\|\\>|\\<|\\\|)+
Where:
[^ \t\\><|] matches any single character but ' ', '\t', and your special characters
\\\\ matches any instance of "\" (i.e. a literal backslash)
\\> matches any instance of ">" (i.e. a literal greater than)
\\< matches any instance of "\<" (i.e. a literal less than)
\\\| matches any instance of "\|" (i.e. a literal vertical bar/pipe)
Actually... You can probably just shorten that rule to:
ARGUMENT ([^ \t\\><|]|\\[^ \t\r\n])+
Where:
[^ \t\\><|] matches any single character but ' ', '\t', and your special characters
\\[^ \t\r\n] matches any character preceded by a '\' in your input except for whitespace (which will handle all of your special characters and allow for literal forms of all other characters)
If you want to allow for literal whitespace in your arguments/parameters then you could shorten the rule even further but be careful with using \\. for the second half of the rule alternation as it may or may not match " \n" (i.e. eat your trailing command terminator character!).
Hope that helps!
You cannot easily extract single escaped characters from a command-line, since you will not know the context of the character. In the simplest case, consider the following:
LessThan:\<
BackslashFrom:\\<
In the first one, < is an escaped character; in the second one, it is not. If your language includes quotes (as most shells do), things become even more complicated. It's a lot better to parse the string left to right, one entity at a time. (I'd use flex myself, because I've stopped wasting my time writing and testing lexers, but you might have some pedagogical reason to do so.)
If you really need to find a special character which shouldn't be special, just search for it (in C++98, where you don't have raw literals, you'll have to escape all of the backslashes):
regex: (\\\\)*\\[<>|]
(An even number -- possibly 0 -- of \, then a \ and a <, > or |)
as a C string => "(\\\\\\\\)*\\\\[<>|]"