In the showwal command-line tool, for unix builds, if the
auxiliary argument is of
the form "Ntruncate" where "N" is a frame number, then truncate the WAL
file after the N-th frame.

FossilOrigin-Name: 90015df30655d884ecf7ae61e588824696954252dc6b1a5f78cf2de8cb236104
diff --git a/tool/showwal.c b/tool/showwal.c
index 33cc218..b214a28 100644
--- a/tool/showwal.c
+++ b/tool/showwal.c
@@ -12,6 +12,7 @@
 
 #if !defined(_MSC_VER)
 #include <unistd.h>
+#include <sys/types.h>
 #else
 #include <io.h>
 #endif
@@ -579,6 +580,14 @@
         decode_btree_page(a, iStart, hdrSize, zLeft+1);
         free(a);
         continue;
+#if !defined(_MSC_VER)
+      }else if( zLeft && strcmp(zLeft,"truncate")==0 ){
+        /* Frame number followed by "truncate" truncates the WAL file
+        ** after that frame */
+        off_t newSize = 32 + iStart*(pagesize+24);
+        truncate(argv[1], newSize);
+        continue;
+#endif
       }else{
         iEnd = iStart;
       }