ereg_replace - allowing only numbers and chars

[Jack_McSlay]

can anyone tell me how do I use the function, or any other, to change anything that's not a letter or number into "_" on a string?

and I would be grateful if anyone could point out a decent documentation on this function for further reference, the one in the official doccumentation is $¨%@&

[Matt_Kindig]

$out=eregi_replace('[^a-z^0-9]','_',$searchThis);