How do I detect if a number has a minus sign?

algonquin has asked for the wisdom of the Perl Monks concerning the following question:

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Re: regex by duff (Parson) on Sep 22, 2004 at 16:15 UTC
perldoc -q 'is a number' has some clues :-) duff	[reply]
Re: regex by jbware (Chaplain) on Sep 22, 2004 at 16:13 UTC
This should probably get you started. `use strict; while (<DATA>) { #OLDmy ($sign, $num, $den) = m@(-)?(\d+)/?(\d)@; my ($sign, $num, $den) = m@(-)?(\d+)(?:/(\d+))?@; print "sign:$sign numerator:$num denominator:$den\n"; } __DATA__ 23 -35 -23/43 2/3 5/` [download] -jbWare Update:*Fixed regex based on ikegami's suggestion. Also pulled / out of the denominator in ikegami's regex.	[reply] [d/l]
Re^2: regex by ikegami (Patriarch) on Sep 22, 2004 at 16:17 UTC
slight change: `m@(-)?(\d+)(?:(/\d+)?)@;` Yours matched "5/".	[reply] [d/l]
Re^2: regex by algonquin (Sexton) on Sep 22, 2004 at 16:47 UTC
Thanks for your input. However it didn't help much. Let me give some more detail. I read -845, 4/3, and 1.25 into three variables $first, $second, $third. I want to be able to distinguish them: if ("it starts with a minus sign"){do something}; if ("it has / in it (fraction)") {do something}; if ("it contains three digits (may or may not start with minus sign)") {do something}; If it is too hard don't worry. Thanks anyways to all that replied.	[reply]
Re^3: regex by ikegami (Patriarch) on Sep 22, 2004 at 17:07 UTC
List this? `foreach (qw( -845 4/3 1.25 )) { /^[-+]?\d{3}$/ && do { print("$_ is a three digit integer, with a possible sign.\n"); #next; }; /^-/ && do { print("$_ starts with a minus sign\n"); #next; }; /\// && do { print("$_ has a / in it.\n"); #next; }; } __END__ output ====== -845 is a three digit integer, with a possible sign. -845 starts with a minus sign 4/3 has a / in it.` [download] Uncomment the `next`s if you want numbers to only match one case.	[reply] [d/l] [select]
Re^3: regex by periapt (Hermit) on Sep 22, 2004 at 17:24 UTC
Actually, you pretty much have it at this point. $sign, $num & $den contain the info you need. A series of decision statements should handle the rest (how you implement the decision tree is highly dependant on your purpose) so ... `if($sign eq '-'){ do something ... } if(not $den){ do something .... } # $den will be undefined if no denom +inator is found if(length($num_ == 3){ do something ... }` [download] There are any number of ways you can identify/validate conditions on your term. (duff's reference has several). The idea is to peel off the parts of your test value that you need into seperate variables and then check the conditions individually. I have found that trying to find some super regex that does it all isn't worth the effort (although it can be aesthetically pleasing) PJ use strict; use warnings; use diagnostics; (if needed)	[reply] [d/l]
Re: How do I detect if a number has a minus sign? by TedPride (Priest) on Sep 22, 2004 at 22:53 UTC
To convert a fraction to decimal equivalent (or approximation, if the fraction doesn't divide out cleanly): `if ($fraction =~ /^((-) ?)?((\d+) )?(\d+) ?\/ ?(\d+)$/) { $fraction = ($2 ? -1 : 1) * ($4 + $5 / $6); }` [download] To test for a negative: `if ($fraction =~ /^((-) ?)?((\d+) )?(\d+) ?\/ ?(\d+)$/ && $2) { #run if negative... }` [download]	[reply] [d/l] [select]

use strict; use warnings; use diagnostics; (if needed)