bug#48680: "zgrep -q" failing with some large files

[David Yoder]

SHORT ANSWER:
Because your results are so different from mine, I tried reproducing on a 
personal machine. I tried 
 * the installed Debian stable gzip 1.9
 * downloading the latest gzip 1.10 packaged source
 * the git master head
With all three I reproduce your results. And the reason is that zgrep doesn't 
support bzip2, so zgrep greps the compressed file and "grep -q fox" doesn't 
match, as expected.

This change is in the SuSE 12 installed zgrep and is not in your upstream gzip 
release or git repository. I guess it's a patch added by SuSE? Do you know 
anything about it?
@@ -198,10 +198,24 @@

 for i
 do
+  case $i in
+    *.bz2)
+      uncompress=bzip2
+      ;;
+       *.xz)
+      uncompress=xz
+      ;;
+    *.lzma)
+      uncompress=lzma
+      ;;
+    *)
+      uncompress=gzip
+      ;;
+  esac
   # Fail if gzip or grep (or sed) fails.
   gzip_status=$(
     exec 5>&1
-    (gzip -cdfq -- "$i" 5>&-; echo $? >&5) 3>&- |
+    ($uncompress -cdfq -- "$i" 5>&-; echo $? >&5) 3>&- |
     if test $files_with_matches -eq 1; then
       eval "$grep" >/dev/null && { printf '%s\n' "$i" || exit 2; }
     elif test $files_without_matches -eq 1; then


DETAILS/ANSWERS:
What platform are you running on? Who built zgrep and gzip on your platform? In 
what directories are the zgrep and gzip executables? What is the output of 
"gzip --version"?
The platform is SUSE 12 SP5. 
This is on machines at work that I don't administer, but zgrep and gzip are 
both from a package named gzip-1.10-2.12.x86_64. This looks like the package 
from SUSE: 
https://scc.suse.com/packages?arch=x86_64&name=SUSE+Linux+Enterprise+Server&package_id=19647018&query=gzip&version=12.5

vl-dyoder-ecdca:~>cat /etc/release
SUSE Linux Enterprise Server 12 (x86_64) 12.5
>rpm -qf /usr/bin/zgrep
gzip-1.10-2.12.x86_64
vl-dyoder-ecdca:~>which zgrep
/usr/bin/zgrep
vl-dyoder-ecdca:~>which gzip
/usr/bin/gzip
vl-dyoder-ecdca:~>gzip --version
gzip 1.10
Copyright (C) 2018 Free Software Foundation, Inc.
Copyright (C) 1993 Jean-loup Gailly.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <https://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Written by Jean-loup Gailly.



What is the output of the following shell command?   unset BASH_ENV; bash -x 
./zgrep -q fox synthetic.log.bz2

>unset BASH_ENV; bash -x zgrep -q fox synthetic.log.bz2
+ grep='${GREP-'\''/usr/bin/grep'\''}'
+ version='zgrep (gzip) 1.10
Copyright (C) 2010-2018 Free Software Foundation, Inc.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <https://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Written by Jean-loup Gailly.'
+ usage='Usage: zgrep [OPTION]... [-e] PATTERN [FILE]...
Look for instances of PATTERN in the input FILEs, using their
uncom
OPTIONs are the same as for '\''grep'\'', except that the following '\''grep'\''
options are not supported: --dereference-recursive (-R), --directories (-d),
--exclude, --exclude-from, --exclude-dir, --include, --null (-Z),
--null-data (-z), and --recursive (-r).

Report bugs to <bug-gzip@gnu.org>.'
+ escape='
  s/'\''/'\''\\'\'''\''/g
  $s/$/'\''/
'
+ operands=
+ have_pat=0
+ files_with_matches=0
+ files_without_matches=0
+ no_filename=0
+ with_filename=0
+ pattmp=
+ test 3 -ne 0
+ option=-q
+ shift
+ optarg=
+ case $option in
+ case $option in
+ case $option in
+ option=''\''-q'\'''
+ grep='${GREP-'\''/usr/bin/grep'\''} '\''-q'\'''
+ test 2 -ne 0
+ option=fox
+ shift
+ optarg=
+ case $option in
+ case $option in
+ operands=' '\''fox'\'''
+ continue
+ test 1 -ne 0
+ option=synthetic.log.bz2
+ shift
+ optarg=
+ case $option in
+ case $option in
+ operands=' '\''fox'\'' '\''synthetic.log.bz2'\'''
+ continue
+ test 0 -ne 0
+ eval 'set --  '\''fox'\'' '\''synthetic.log.bz2'\'' ${1+"$@"}'
++ set -- fox synthetic.log.bz2
+ test 0 -eq 0
+ case ${1?"missing pattern; try \`$0 --help' for help"} in
+ grep='${GREP-'\''/usr/bin/grep'\''} '\''-q'\'' -- '\''fox'\'''
+ shift
+ test 1 -eq 0
+ exec
+ res=1
+ for i in '"$@"'
+ case $i in
+ uncompress=bzip2
++ exec
++ bzip2 -cdfq -- synthetic.log.bz2
++ test 0 -eq 1
++ test 0 -eq 1
++ test 0 -eq 0
++ test 1 -eq 1
++ eval '${GREP-'\''/usr/bin/grep'\''} '\''-q'\'' -- '\''fox'\'''
+++ /usr/bin/grep -q -- fox
++ echo 141
+ gzip_status=141
+ r=0
+ test 141 -eq 2
+ test 141 -eq 1
+ test 0 -lt 141
+ r=141
+ test 141 -le 1
+ test 1 -lt 141
+ res=141
+ test 126 -le 141
+ break
+ test -n ''
+ test 128 -le 141
++ expr 141 % 128
+ kill -13 3053