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EvanKEvanK
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- current working pattern, broken into pieces as separate files - working tests + test helper script - working build script, to compile multiline pattern into single line
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‎README.md

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# AWS EventBridge Schedule Expression Validation with Regular Expressions
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As this is intended for use in CloudFormation templates (as an `AllowedPattern`), we are aiming for compatibility with [Java's regular expression syntax](https://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html).
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However, due to the massive complexity and sheer scope of the overall expression we are maintiaining here, it will be broken up into various pieces for the `cron()` portion and versioned as native Perl regex.
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The most recent working version of this pattern is also available (with unit tests!) on [Regex101](https://regex101.com/r/YHscM3/2).
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## Project Structure
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The complete pattern can be found in `main.pl`, in two different forms and assigned to two different global variables:
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- `$expanded` - here, the complete pattern is broken out across multiple lines and commented heavily (using the `/x` flag) for readability
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- `$collapsed` - here, any non-leading and non-trailing comments and whitespace have been removed, making it fit for copy and paste elsewhere
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Due to the complexity of the `cron()` matching, each individual _field_ of the cron format has been broken out into its own file under the `cron` directory:
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```
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./cron
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├── daysofmonth.pl
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├── daysofweek.pl
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├── hours.pl
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├── minutes.pl
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├── months.pl
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└── years.pl
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```
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These individual field patterns are then merged back into the main pattern manually.
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## Testing
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Currently, several valid `rate` and `cron` patterns are recorded as "positive" test cases as well as several invalid patterns as "negative" cases in tab delimited files under the `tests` directory.
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You can test them against the latest complete patterns (again, housed in `main.pl`) by running the test script:
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```shell
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perl test.pl
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# outputs TAP formatted results...
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```
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## Building
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The current multiline pattern can be condensed into a single line format (and compared against the currently versioned collapsed pattern) by running the build script:
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> Note: you may need to install the `Text::Diff` CPAN module in order for this script to run successfully
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```shell
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perl build.pl
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# prints a diff if anything in the main pattern has changed
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# subsequently prints the condensed pattern to stdout
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```

‎build.pl

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use strict;
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use warnings;
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use Term::ANSIColor qw(:constants);
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use Text::Diff;
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require "./main.pl";
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our ($expanded, $collapsed);
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# remove the wrappings from qr//
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my $pattern = $expanded =~ s/(^\(\?\^x\:\n+|\n+\)$)//rg;
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# remove any whole single line comments (at ANY indent)
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$pattern =~ s/\n([ \t]*[#][^\n]+\n)+/\n/g;
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# remove any indents
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$pattern =~ s/^[ \t]*//gm;
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# remove rest of newlines
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$pattern =~ s/\n//g;
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my %options = (
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STYLE => "Unified",
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OUTPUT => \*STDOUT,
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FILENAME_A => 'Existing',
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FILENAME_B => 'New'
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);
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# get existing collapsed pattern to compare against
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my $expected = $collapsed =~ s/(^\(\?\^x\:\n+|\n+\)$)//rg;
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if ($expected eq $pattern) {
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print BRIGHT_GREEN ON_BLACK "No changes detected!\n", RESET;
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} else {
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print BRIGHT_RED ON_BLACK "Differences detected:\n", RESET;
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diff \$expected, \$pattern, \%options;
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}
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print "\nCompiled pattern:\n\n$pattern\n\n";

‎cron/daysofmonth.pl

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# full field
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/
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#### top-level days of month field
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# field, any number of expressions broken by literal comma
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(?:
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### first unit expression, either range of two units or increment of a single unit
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## first single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end single day of month unit
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# optional second unit (range) or increment
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(?:
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# range, a literal dash followed by ANOTHER single unit
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(?:
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[-]
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## second single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end second single day of month unit
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)
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|
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# OR increment, a literal slash followed by integer increment value
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(?:
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[/]
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[0-9]+
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)
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)?
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### end first unit expression
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(?:
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[,]
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### second unit expression, either range of two units or increment of a single unit
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## first single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end single day of month unit
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# optional second unit (range) or increment
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(?:
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# range, a literal dash followed by ANOTHER single unit
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(?:
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[-]
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## second single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end second single day of month unit
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)
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|
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# OR increment, a literal slash followed by integer increment value
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(?:
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[/]
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[0-9]+
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)
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)?
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### end second unit expression
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)*
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)
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#### end top-level days of month field
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/x;
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# unit expression
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/
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### unit expression, either range of two units or increment of a single unit
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## first single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end single day of month unit
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# optional second unit (range) or increment
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(?:
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# range, a literal dash followed by ANOTHER single unit
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(?:
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[-]
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## second single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end second single day of month unit
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)
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|
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# OR increment, a literal slash followed by integer increment value
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(?:
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[/]
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[0-9]+
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)
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)?
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### end unit expression
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/x;
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# single unit
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/
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## single day of month unit
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(?:
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(?:
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# number (roughly) between 1-31
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(?:
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# single digit num from 0-9 OR double digit num whose first digit is between 1 and 3
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[1-3]?
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[0-9]
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)
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# followed by zero or one W wildcard (weekday)
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W?
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)
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|
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# OR ordered combo of L and W wildcards (last weekday of month)
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LW
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|
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# OR standalone wildcard of L (last day of month) or asterisk (any)
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[L*]
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)
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## end single day of month unit
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/x;

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