Added expr, from Edward Betts <edward@debian.org>, with some fixups

and docs added by me.
 -Erik

1 files changed, 52 insertions, 0 deletions

diff --git a/docs/busybox.sgml b/docs/busybox.sgml
index ec6f5041d..a25aa0189 100644
--- a/docs/busybox.sgml
+++ b/docs/busybox.sgml
@@ -879,6 +879,58 @@
 		</para>
 	</sect1>
 
+	<sect1 id="expr">
+	    <title>expr</title>
+
+		<para>
+		Usage: expr EXPRESSION
+		</para>
+
+		<para>
+		Prints the value of EXPRESSION to standard output.
+		</para>
+
+		<para>
+		EXPRESSION may be:
+		</para>
+
+		<para>
+		<screen>
+			ARG1 |  ARG2    ARG1 if it is neither null nor 0, otherwise ARG2
+			ARG1 &  ARG2    ARG1 if neither argument is null or 0, otherwise 0
+			ARG1 &lt  ARG2    ARG1 is less than ARG2
+			ARG1 &lt= ARG2    ARG1 is less than or equal to ARG2
+			ARG1 =  ARG2    ARG1 is equal to ARG2
+			ARG1 != ARG2    ARG1 is unequal to ARG2
+			ARG1 &gt= ARG2    ARG1 is greater than or equal to ARG2
+			ARG1 &gt  ARG2    ARG1 is greater than ARG2
+			ARG1 +  ARG2    arithmetic sum of ARG1 and ARG2
+			ARG1 -  ARG2    arithmetic difference of ARG1 and ARG2
+			ARG1 *  ARG2    arithmetic product of ARG1 and ARG2
+			ARG1 /  ARG2    arithmetic quotient of ARG1 divided by ARG2
+			ARG1 %  ARG2    arithmetic remainder of ARG1 divided by ARG2
+			STRING : REGEXP             anchored pattern match of REGEXP in STRING
+			match STRING REGEXP         same as STRING : REGEXP
+			substr STRING POS LENGTH    substring of STRING, POS counted from 1
+			index STRING CHARS          index in STRING where any CHARS is found, or 0
+			length STRING               length of STRING
+			quote TOKEN                 interpret TOKEN as a string, even if it is a
+							keyword like `match' or an operator like `/'
+			( EXPRESSION )              value of EXPRESSION
+		</screen>
+		</para>
+
+		<para>
+		Beware that many operators need to be escaped or quoted for shells.
+		Comparisons are arithmetic if both ARGs are numbers, else
+		lexicographical.  Pattern matches return the string matched between
+		\( and \) or null; if \( and \) are not used, they return the number
+		of characters matched or 0.
+		</para>
+
+	</sect1>
+
+
 	<sect1 id="false">
 	    <title>false</title>