Truncate files written with "-o".

docs/pv.1

@@ -348,7 +348,7 @@ invocations in a single, long, pipeline.
 Write data to
 .I FILE
 rather than standard output.  If the file already exists, it will be
-overwritten from the start, but not truncated.
+truncated.
 .TP
 .BI \-L\  RATE \fR,\ \fB\-\-rate-limit\  RATE
 Limit the transfer to a maximum of

docs/pv.1.md

@@ -260,8 +260,7 @@ that are explicitly switched on will be shown.
 **-o FILE, \--output FILE**
 
 :   Write data to *FILE* rather than standard output. If the file
-    already exists, it will be overwritten from the start, but not
-    truncated.
+    already exists, it will be truncated.
 
 **-L RATE, \--rate-limit RATE**
 

src/main/main.c

@@ -306,7 +306,7 @@ int main(int argc, char **argv)
 	if (NULL == opts->output || 0 == strcmp(opts->output, "-")) {
 		pv_state_output_set(state, STDOUT_FILENO, "(stdout)");
 	} else {
-		int fd = open(opts->output, O_WRONLY | O_CREAT, 0600);	/* flawfinder: ignore */
+		int fd = open(opts->output, O_WRONLY | O_CREAT | O_TRUNC, 0600);	/* flawfinder: ignore */
 		/*
 		 * flawfinder rationale: the output filename has been
 		 * explicitly provided, and in many cases the operator will