This patch to zgrep script fixes a problem with empty pattern:

	zgrep -n "" file.gz

--- /usr/bin/zgrep	Wed Nov 20 11:13:29 2002
+++ zgrep	Wed Jan  8 11:27:17 2003
@@ -31,6 +31,7 @@
 esac
 
 pat=""
+pat_set=0
 after_dash_dash=""
 files_with_matches=0
 files_without_matches=0
@@ -63,15 +64,15 @@
 	esac;;
   esac
   case "$after_dash_dash$1" in
-  -[ef])   opt="$opt $1"; shift; pat="$1"
+  -[ef])   opt="$opt $1"; shift; pat="$1"; pat_set=1
            if test "$grep" = grep; then  # grep is buggy with -e on SVR4
              grep=egrep
            fi;;
   -[ABCdm])opt="$opt $1 $2"; shift;;
   --)      opt="$opt $1"; after_dash_dash=1;;
   -*)	   opt="$opt $1";;
-   *)      if test -z "$pat"; then
-	     pat="$1"
+   *)      if test $pat_set -eq 0; then
+	     pat="$1"; pat_set=1
 	   else
 	     break;
            fi;;
@@ -79,7 +80,7 @@
   shift
 done
 
-if test -z "$pat"; then
+if test $pat_set -eq 0; then
   echo "grep through gzip files" 1>&2
   echo "usage: $prog [grep_options] pattern [files]" 1>&2
   exit 1