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+#From: jrmartin@rainey.blueneptune.com (James R. Martin)
+#Newsgroups: comp.unix.shell
+#Subject: Re: testing user input on numeric or character value
+#Date: 26 Nov 1997 01:28:43 GMT
+
+# isnum returns True if its argument is a valid number,
+# and False (retval=1) if it is any other string.
+# The first pattern requires a digit before the decimal
+# point, and the second after the decimal point.
+
+# BASH NOTE: make sure you have executed `shopt -s extglob' before
+# trying to use this function, or it will not work
+
+function isnum # string
+{
+    case $1 in
+    ?([-+])+([0-9])?(.)*([0-9])?([Ee]?([-+])+([0-9])) )
+        return 0;;
+    ?([-+])*([0-9])?(.)+([0-9])?([Ee]?([-+])+([0-9])) )
+        return 0;;
+    *) return 1;;
+    esac
+}