Validating with regular expressions

I have a regex that works, but only for positive values. There are lots of perfectly valid currencies that do not have a dollar sign. Instead I might just eliminate all the non-numeric characters and see if it passes the is_numeric() test.

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Introduction Brief History of Regular Expressions Simple Expressions Quantifiers Metacharacters Character Classes Predefined Set Metacharacters Sample Expressions Validation in ASP.

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Whether you need to validate user input, search for patterns within strings, or reformat text in powerful ways, regular expressions can help.

Assume that this regex will be used for a public URL shortener written in PHP, so URLs like shouldn’t pass (even though they’re technically valid).

Also, in this case I only want to allow the HTTP, HTTPS and FTP protocols. :ac|ad|aero|ae|af|ag|ai|al|am|an|ao|aq|arpa|ar|asia|as|at|au|aw|ax|az|ba|bb|bd|be|bf|bg|bh|biz|bi|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|cat|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|coop|com|co|cr|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gg|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|im|info|int|in|io|iq|ir|is|it|je|jm|jobs|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|me|mg|mh|mil|mk|ml|mm|mn|mobi|mo|mp|mq|mr|ms|mt|museum|mu|mv|mw|mx|my|mz|name|na|nc|net|ne|nf|ng|ni|nl|no|np|nr|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pro|pr|ps|pt|pw|py|qa|re|ro|rs|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tel|tf|tg|th|tj|tk|tl|tm|tn|to|tp|travel|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|xn--0zwm56d|xn--11b5bs3a9aj6g|xn--80akhbyknj4f|xn--9t4b11yi5a|xn--deba0ad|xn--g6w251d|xn--hgbk6aj7f53bba|xn--hlcj6aya9esc7a|xn--jxalpdlp|xn--kgbechtv|xn--zckzah|ye|yt|yu|za|zm|zw)|(?

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