Concatenate regular and gzip-compressed files at the same time.
Assume that we want to feed regular and gzip-compressed files to an unspecified applications.
$ ls /var/log/apt/history.log*
/var/log/apt/history.log /var/log/apt/history.log.1.gz
It does not work at first.
$ zcat /var/log/apt/history.log*
gzip: /var/log/apt/history.log: unexpected end of file
Inspect zcat help information.
$ zcat --help
Usage: /usr/bin/zcat [OPTION]... [FILE]...
Uncompress FILEs to standard output.
-f, --force force; read compressed data even from a terminal
-l, --list list compressed file contents
-q, --quiet suppress all warnings
-r, --recursive operate recursively on directories
-S, --suffix=SUF use suffix SUF on compressed files
--synchronous synchronous output (safer if system crashes, but slower)
-t, --test test compressed file integrity
-v, --verbose verbose mode
--help display this help and exit
--version display version information and exit
With no FILE, or when FILE is -, read standard input.
Report bugs to <bug-gzip@gnu.org>.
Force execution, so the uncompressed data will be copied to the standard output.
$ zcat --force /var/log/apt/history.log*
Start-Date: 2021-04-19 19:24:18 Commandline: apt install mariadb-server mariadb-client Requested-By: vagrant (1000) Install: libtimedate-perl:amd64 (2.3300-2, automatic), libhtml-tagset-perl:amd64 (3.20-4, automatic), mariadb-server:amd64 (1:10.5.9-1), libdbi-perl:amd64 (1.643-3+b1, automatic), libfcgi-perl:amd64 (0.79+ds-2, automatic), libdbd-mariadb-perl:amd64 (1.21-3, automatic), galera-4:amd64 (26.4.7-3, automatic), mysql-common:amd64 (5.8+1.0.7, automatic), libencode-locale-perl:amd64 (1.05-1.1, automatic), libsigsegv2:amd64 (2.13-1, automatic), liblwp-mediatypes-perl:amd64 (6.04-1, automatic), libmpfr6:amd64 (4.1.0-3, automatic), psmisc:amd64 (23.4-2, automatic), mariadb-server-core-10.5:amd64 (1:10.5.9-1, automatic), libhtml-template-perl:amd64 (2.97-1.1, automatic), gawk:amd64 (1:5.1.0-1, automatic), liburi-perl:amd64 (5.08-1, automatic), libfcgi0ldbl:amd64 (2.4.2-2, automatic), libio-html-perl:amd64 (1.004-2, automatic), libsnappy1v5:amd64 (1.1.8-1, automatic), libterm-readkey-perl:amd64 (2.38-1+b2, automatic), libhttp-date-perl:amd64 (6.05-1, automatic), rsync:amd64 (3.2.3-4, automatic), mariadb-client-10.5:amd64 (1:10.5.9-1, automatic), libhtml-parser-perl:amd64 (3.75-1+b1, automatic), libcgi-fast-perl:amd64 (1:2.15-1, automatic), libconfig-inifiles-perl:amd64 (3.000003-1, automatic), mariadb-common:amd64 (1:10.5.9-1, automatic), libmariadb3:amd64 (1:10.5.9-1, automatic), mariadb-client:amd64 (1:10.5.9-1), libclone-perl:amd64 (0.45-1+b1, automatic), socat:amd64 (1.7.4.1-3, automatic), mariadb-server-10.5:amd64 (1:10.5.9-1, automatic), libhttp-message-perl:amd64 (6.28-1, automatic), libfcgi-bin:amd64 (2.4.2-2, automatic), libcgi-pm-perl:amd64 (4.51-1, automatic), mariadb-client-core-10.5:amd64 (1:10.5.9-1, automatic) End-Date: 2021-04-19 19:24:26 [...] Start-Date: 2021-04-24 06:54:25 Commandline: /usr/bin/unattended-upgrade Upgrade: dpkg:amd64 (1.20.7.1, 1.20.9) End-Date: 2021-04-24 06:54:26 Start-Date: 2021-04-24 13:53:19 Commandline: apt install vim Requested-By: vagrant (1000) Install: vim:amd64 (2:8.2.2434-3), libgpm2:amd64 (1.20.7-8, automatic), vim-runtime:amd64 (2:8.2.2434-3, automatic) End-Date: 2021-04-24 13:53:20
It works, but let’s not stop there and check this command more closely.
$ which zcat
/usr/bin/zcat
It is a shell script, which is interesting.
$ file /usr/bin/zcat
/usr/bin/zcat: POSIX shell script, ASCII text executable
Inspect this shell script.
$ cat /usr/bin/zcat
#!/bin/sh
# Uncompress files to standard output.
# Copyright (C) 2007, 2010-2018 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
version="zcat (gzip) 1.10
Copyright (C) 2007, 2011-2018 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 Paul Eggert."
usage="Usage: $0 [OPTION]... [FILE]...
Uncompress FILEs to standard output.
-f, --force force; read compressed data even from a terminal
-l, --list list compressed file contents
-q, --quiet suppress all warnings
-r, --recursive operate recursively on directories
-S, --suffix=SUF use suffix SUF on compressed files
--synchronous synchronous output (safer if system crashes, but slower)
-t, --test test compressed file integrity
-v, --verbose verbose mode
--help display this help and exit
--version display version information and exit
With no FILE, or when FILE is -, read standard input.
Report bugs to <bug-gzip@gnu.org>."
case $1 in
--help) printf '%s\n' "$usage" || exit 1; exit;;
--version) printf '%s\n' "$version" || exit 1; exit;;
esac
exec gzip -cd "$@"
It is simply executing gzip utility, so you use it directly to get the same effect.
$ gzip --stdout --decompress --force /var/log/apt/history.log*
Start-Date: 2021-04-19 19:24:18 Commandline: apt install mariadb-server mariadb-client Requested-By: vagrant (1000) Install: libtimedate-perl:amd64 (2.3300-2, automatic), libhtml-tagset-perl:amd64 (3.20-4, automatic), mariadb-server:amd64 (1:10.5.9-1), libdbi-perl:amd64 (1.643-3+b1, automatic), libfcgi-perl:amd64 (0.79+ds-2, automatic), libdbd-mariadb-perl:amd64 (1.21-3, automatic), galera-4:amd64 (26.4.7-3, automatic), mysql-common:amd64 (5.8+1.0.7, automatic), libencode-locale-perl:amd64 (1.05-1.1, automatic), libsigsegv2:amd64 (2.13-1, automatic), liblwp-mediatypes-perl:amd64 (6.04-1, automatic), libmpfr6:amd64 (4.1.0-3, automatic), psmisc:amd64 (23.4-2, automatic), mariadb-server-core-10.5:amd64 (1:10.5.9-1, automatic), libhtml-template-perl:amd64 (2.97-1.1, automatic), gawk:amd64 (1:5.1.0-1, automatic), liburi-perl:amd64 (5.08-1, automatic), libfcgi0ldbl:amd64 (2.4.2-2, automatic), libio-html-perl:amd64 (1.004-2, automatic), libsnappy1v5:amd64 (1.1.8-1, automatic), libterm-readkey-perl:amd64 (2.38-1+b2, automatic), libhttp-date-perl:amd64 (6.05-1, automatic), rsync:amd64 (3.2.3-4, automatic), mariadb-client-10.5:amd64 (1:10.5.9-1, automatic), libhtml-parser-perl:amd64 (3.75-1+b1, automatic), libcgi-fast-perl:amd64 (1:2.15-1, automatic), libconfig-inifiles-perl:amd64 (3.000003-1, automatic), mariadb-common:amd64 (1:10.5.9-1, automatic), libmariadb3:amd64 (1:10.5.9-1, automatic), mariadb-client:amd64 (1:10.5.9-1), libclone-perl:amd64 (0.45-1+b1, automatic), socat:amd64 (1.7.4.1-3, automatic), mariadb-server-10.5:amd64 (1:10.5.9-1, automatic), libhttp-message-perl:amd64 (6.28-1, automatic), libfcgi-bin:amd64 (2.4.2-2, automatic), libcgi-pm-perl:amd64 (4.51-1, automatic), mariadb-client-core-10.5:amd64 (1:10.5.9-1, automatic) End-Date: 2021-04-19 19:24:26 [...] Start-Date: 2021-04-24 06:54:25 Commandline: /usr/bin/unattended-upgrade Upgrade: dpkg:amd64 (1.20.7.1, 1.20.9) End-Date: 2021-04-24 06:54:26 Start-Date: 2021-04-24 13:53:19 Commandline: apt install vim Requested-By: vagrant (1000) Install: vim:amd64 (2:8.2.2434-3), libgpm2:amd64 (1.20.7-8, automatic), vim-runtime:amd64 (2:8.2.2434-3, automatic) End-Date: 2021-04-24 13:53:20
It is a small thing, but an interesting one.
