Question 257063 in Javascript Question posted in
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Javascript – Regex to match Postgres "operator name" rules

I’m trying (and failing) to write a JavaScript regular expression to match a PostgreSQL operator name, defined in the docs as:

An operator name is a sequence of up to NAMEDATALEN-1 (63 by default) characters from the following list:

+ - * / < > = ~ ! @ # % ^ & | ` ?

There are a few restrictions on operator names, however:

  • — and /* cannot appear anywhere in an operator name, since they will be taken as the start of a comment.

  • A multiple-character operator name cannot end in + or -, unless the name also contains at least one of these characters:

    ! @ # % ^ & | ` ?

    For example, @- is an allowed operator name, but *- is not. This restriction allows PostgreSQL to parse SQL-compliant queries without requiring spaces between tokens.

Other than the Regex-noob:

[+-*/<>=~!@#%^&|`?]+

I’m failing hard to get any further, especially the "-- and /* can’t appear in the matched string" requirements. I’ve tried wrestling Regular expression to match a line that doesn't contain a word into it, but with no success.

Is this even possible all in a single Regex? (it’s to work within the https://github.com/no-context/moo so no opportunity fallback to regular JS).

Any pointers very gratefully received!

I’ve tried things like (?!.*--)[+-*/<>=~!@#%^&|?]+`, but to no avail.

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2

Answers


  1. 0

    First of all, in a character class none of these except - (and ^, if it were at the beginning) need to be backslash-escaped, so you can simplify to

    /[+-*/<>=~!@#%^&|`?]+/

    To avoid matching comments, the easiest solution is lookahead:

    /(?:(?!--|/*)[+-*/<>=~!@#%^&|`?])+/

    but you can also spell it out to something like "- followed by a valid character except -, or / followed by a valid character except -, or valid character except - or /", but that gets complicated quickly with repetition still not forming forbidden patterns.

    For "cannot end in + or -, unless it also contains at least one […]", you can also use lookaround:

    /(?=.*[~!@#%^&|`?]|.*[^+-]$)(?:(?!--|/*)[+-*/<>=~!@#%^&|`?])+/

    But given you want to use this for a lexer, the $ anchor probably does not work so you’ll need to use

    /(?:(?!--|/*)[+-*/<>=~!@#%^&|`?])+(?<![+-])|[+-]|(?:(?!--|/*)[+-*/<>=~!@#%^&|`?])*[~!@#%^&|`?](?:(?!--|/*)[+-*/<>=~!@#%^&|`?])*/
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  2. 0

    This regex will capture operator names from a multi-line string.

    /(?:^|[t ])(?!S*?(?:--|/*))(?![+-*/<>=]+[+-](?=[ n]))([+-*/<>=~!@#%^&|`?]{1,63})/gm

    Breakdown:

    (?:^|[t ])           <- Operator name is at start of line or is preceded by whitespace.
((?!S*?(?:--|/*))  <- It may not contain "--" or "/*"
(?![+-*/<>=]+[+-](?=[ n]))  
                      <- May not end in "+" or "-" if missing certain characters.
                         Word boundaries don't work with these special characters, so 
                         we detect by looking for space or newline following our name.
([+-*/<>=~!@#%^&|`?]{1,63})
                      <- Contains a sequence of 1 to 63 of a set of allowed characters.

    Tested against the following data:

    [GOOD]
-
+ +
* *<
/ < > >*
= ~ !
@ # % ^
& | < >
*->
[BAD]
--
/*
+--
@/*
*-
<+
++
[MIX]
!!@ #/*
#/* !!@
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