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Bash Cheatsheat

Introduction

Vocab

Basic shell Features

Syntax

Basic commands

  • POSIX : a set of standards for UNIX based operating systems
  • blank : a space or a tab character
  • builtin : a command that is built into the shell itself, rather than relying on an external command
  • control operator : a token that performs a task. It can be a newline or any of the following
  • ||
  • &&
  • &
  • ;
  • ;;
  • |
  • |&
  • (
  • =)=
  • exit status : is the numerical value a command returns to its caller. It can be [0-255]
  • field : is a unit of text that is the result of shell expansion. The resulting field can be used as commands
    • or arguments
  • job : a collection of processes that makes up a pipeline and any processes that that pipeline spawns
  • job control : a method that allows users to start/stop execution of precesses
  • metacharacter : a char, that when unquoted seperates words. A metachar is a blank or any of the following
  • |
  • &
  • ;
  • (
  • =)=
  • <
  • >
  • name : a words beginning with a letter or underscore and consisting of alphanumeric chars and underscores
  • operator : a control operator or a redirection operation
  • process group : a collection of processes that each have the same group ID
  • process groupID : an ID that binds related processes in a group
  • reserved word : words that means things to the shell like for, while, if
  • return status : exit status
  • signal : a method, by which a process can be notified of something from the kernal
  • special builtin : a shell builtin that is deemed special by POSIX
  • token : sequence of characters considered a single unit by the shell. It is either a word or an operator
  • word : a sequence of chars considered a unit by the shell not including unquoted metachars
  • Anything inside single quotes shall not be expanded. Also '\'' is NOT permitted in bash
  • Double quotes preserved the literal value of whatever's in the string, except for
  • $
  • `
  • *
  • @
    • Are words seperated by blanks terminated by one of the shell's control operators So,

#+BEGIN_SRC sh echo "523" #+END_SRC

#+RESULTS:

523

Pipelines

has the command echo seperated by a blank space, followed by the string, which is its arguement. Newline is the operator that terminates the command. [ time ] [ ! ] command1 [ | or |& command 2 ] ...

This is what makes shell scripting really powerful. You can make one command be another command's input. So here's a simple example

#+BEGIN_SRC sh ls | grep "the" #+END_SRC

lists of commands

    This lists the files in the currect directory and that output becames grep's input. Cool eh? a list is a sequence of pipelines seperated by one of the following operators
  • ;
  • &
  • &&
  • ||

They can be optionally terminated by a &, which makes the whole command run in the background, ;, or a newline

A couple of examples

command1 && command2

command2 is only executed if command1 returns 0 (success)

command1 || command2

curly brackets!

command2 is only executed if command1 returns non-0 (error)

So suppose you have this problem:

You want to download all of the logs found on https://bayfront.guixsd.org/.well-known/logs/

The logs are of the form

year-month-day.log

It starts at

2018-08-01.log 2018-08-02.log 2018-08-03.log ... 2018-12-30.log 2018-12-31.log 2019-01-01.log 2019-01-02.log ... 2019-04-15.log 2019-04-16.log

And that is where it ends.

How do you download all of these log files?


wget https://bayfront.guixsd.org/.well-known/logs/*

You will get an error saying that "*" wildcards are not supported in HTTP. That is because HTTP is not designed to act like a filesystem. There is no way to tell a server, show me all the files under this directory. In fact, some servers don't want to show you files, because that is a security risk.

But curly brackets provide a nice way to solve this problem!

But before I solve it, let's show what curly brackets can do?

Let's create 5 files!


touch myfile{1..5}.txt

Sweet. Let's see those files!


ls myfile*

myfile1.txt
myfile2.txt
myfile3.txt
myfile4.txt
myfile5.txt

Ok, let's delete 1 3 and 5.


rm myfile{1,3,5}.txt

Did we do it correctly? We did.


ls myfile*

myfile2.txt
myfile4.txt

To clean up, delete the rest


rm myfile*


ls myfile*

So now that you know the two ways to use curly brackets, here's the solution:


wget https://bayfront.guixsd.org/.well-known/logs/{2019,2018}-{01..12}-{01..31}.log

some bash examples


  var1=1
  var2=2
  var3=3
  var4=4

  if [[ $var1 -lt $var4 ]]; then
      echo "$var1 is less than $var4";
  fi

  if [[ $var3 -gt $var1 ]]; then
      echo "$var3 is greater than $var1";
  fi

  expr $var4 + $var2

enabling important systemd units

1 is less than 4
3 is greater than 1
6

I spent an hour going over all of my systemd unit files


systemctl list-unit-files

UNIT FILE STATE proc-sys-fs-binfmt_misc.automount static org.freedesktop.hostname1.busname static org.freedesktop.import1.busname static org.freedesktop.locale1.busname static org.freedesktop.login1.busname static org.freedesktop.machine1.busname static org.freedesktop.network1.busname static org.freedesktop.resolve1.busname static org.freedesktop.systemd1.busname static org.freedesktop.timedate1.busname static dev-hugepages.mount static dev-mqueue.mount static proc-fs-nfsd.mount static proc-sys-fs-binfmt_misc.mount static sys-fs-fuse-connections.mount static sys-kernel-config.mount static sys-kernel-debug.mount static tmp.mount static var-lib-machines.mount static var-lib-nfs-rpc_pipefs.mount static systemd-ask-password-console.path static systemd-ask-password-wall.path static adb.service disabled alsa-restore.service static alsa-state.service static auth-rpcgss-module.service static autovt@.service enabled avahi-daemon.service disabled avahi-dnsconfd.service disabled blk-availability.service disabled canberra-system-bootup.service disabled canberra-system-shutdown-reboot.service disabled canberra-system-shutdown.service disabled ceph-mds@.service disabled ceph-mon@.service disabled ceph-osd@.service disabled colord.service static console-getty.service disabled console-shell.service disabled container-getty@.service static cpupower.service disabled cronie.service disabled dbus-org.freedesktop.hostname1.service static dbus-org.freedesktop.import1.service static dbus-org.freedesktop.locale1.service static dbus-org.freedesktop.login1.service static dbus-org.freedesktop.machine1.service static dbus-org.freedesktop.network1.service enabled dbus-org.freedesktop.nm-dispatcher.service bad dbus-org.freedesktop.resolve1.service enabled dbus-org.freedesktop.timedate1.service static dbus.service static debug-shell.service disabled deluge-web.service disabled deluged.service disabled dhclient@.service disabled dhcpcd.service disabled dhcpcd@.service disabled dm-event.service disabled dovecot.service disabled emergency.service static fluidsynth.service disabled fstrim.service static ftpd.service disabled geoclue.service static getty@.service enabled git-daemon@.service static github.service disabled gnunet.service disabled gpm.service disabled gssproxy.service disabled haveged.service enabled httpd.service disabled ifplugd@.service disabled initrd-cleanup.service static initrd-parse-etc.service static initrd-switch-root.service static initrd-udevadm-cleanup-db.service static ip6tables.service disabled iptables.service enabled kmod-static-nodes.service static krb5-kadmind.service disabled krb5-kdc.service disabled krb5-kpropd.service disabled krb5-kpropd@.service static laptop-mode.service disabled ldconfig.service static libvirt-guests.service disabled libvirtd.service disabled lircd.service disabled lircmd.service disabled lmt-poll.service disabled logrotate.service static lvm2-lvmetad.service disabled lvm2-monitor.service disabled lvm2-pvscan@.service static man-db.service static mbsync@.service static mkinitcpio-generate-shutdown-ramfs.service static mysqld.service enabled netctl-auto@.service disabled netctl-ifplugd@.service disabled netctl-sleep.service disabled netctl.service disabled netctl@.service static nfs-blkmap.service disabled nfs-config.service static nfs-idmapd.service static nfs-mountd.service static nfs-server.service disabled nfs-utils.service static nginx.service disabled nscd.service disabled pacman-database-mon.service disabled pacman-keyring.service static pdnsd.service disabled php-fpm.service disabled polkit.service static postfix.service disabled prelink-tue.service disabled quotaon.service static rescue.service static rlogin@.service static rpc-gssd.service static rpc-statd-notify.service static rpc-statd.service static rpc-svcgssd.service static rpcbind.service indirect rsh@.service static rsyncd.service disabled rsyncd@.service static rtkit-daemon.service disabled serial-getty@.service disabled shadow.service static sshd.service enabled sshd@.service static sshdgenkeys.service static systemd-ask-password-console.service static systemd-ask-password-wall.service static systemd-backlight@.service static systemd-binfmt.service static systemd-bootchart.service disabled systemd-bus-proxyd.service static systemd-coredump@.service static systemd-exit.service static systemd-firstboot.service static systemd-fsck-root.service static systemd-fsck@.service static systemd-halt.service static systemd-hibernate-resume@.service static systemd-hibernate.service static systemd-hostnamed.service static systemd-hwdb-update.service static systemd-hybrid-sleep.service static systemd-importd.service static systemd-initctl.service static systemd-journal-catalog-update.service static systemd-journal-flush.service static systemd-journal-gatewayd.service indirect systemd-journal-remote.service indirect systemd-journal-upload.service disabled systemd-journald.service static systemd-kexec.service static systemd-localed.service static systemd-logind.service static systemd-machine-id-commit.service static systemd-machined.service static systemd-modules-load.service static systemd-networkd-wait-online.service disabled systemd-networkd.service enabled systemd-nspawn@.service disabled systemd-poweroff.service static systemd-quotacheck.service static systemd-random-seed.service static systemd-reboot.service static systemd-remount-fs.service static systemd-resolved.service enabled systemd-rfkill.service static systemd-suspend.service static systemd-sysctl.service static systemd-sysusers.service static systemd-timedated.service static systemd-timesyncd.service enabled systemd-tmpfiles-clean.service static systemd-tmpfiles-setup-dev.service static systemd-tmpfiles-setup.service static systemd-udev-settle.service static systemd-udev-trigger.service static systemd-udevd.service static systemd-update-done.service static systemd-update-utmp-runlevel.service static systemd-update-utmp.service static systemd-user-sessions.service static systemd-vconsole-setup.service static talk.service indirect telnet@.service static udisks2.service disabled updatedb.service static upower.service disabled usbmuxd.service static user@.service static uuidd.service indirect verynice.service disabled virtlockd.service indirect virtlogd.service indirect wpa_supplicant-nl80211@.service disabled wpa_supplicant-wired@.service disabled wpa_supplicant.service disabled wpa_supplicant@.service disabled x11vnc.service static -.slice static machine.slice static system.slice static user.slice static avahi-daemon.socket disabled dbus.socket static dm-event.socket static dovecot.socket disabled git-daemon.socket disabled krb5-kpropd.socket disabled libvirtd.socket static lircd.socket disabled lvm2-lvmetad.socket static lvmetad.socket masked rlogin.socket disabled rpcbind.socket disabled rsh.socket disabled rsyncd.socket disabled sshd.socket disabled syslog.socket static systemd-bus-proxyd.socket static systemd-coredump.socket static systemd-initctl.socket static systemd-journal-gatewayd.socket disabled systemd-journal-remote.socket disabled systemd-journald-audit.socket static systemd-journald-dev-log.socket static systemd-journald.socket static systemd-networkd.socket enabled systemd-rfkill.socket static systemd-udevd-control.socket static systemd-udevd-kernel.socket static talk.socket disabled telnet.socket disabled uuidd.socket disabled virtlockd.socket disabled virtlogd.socket disabled basic.target static bluetooth.target masked busnames.target static cryptsetup-pre.target static cryptsetup.target static ctrl-alt-del.target disabled default.target static emergency.target static exit.target disabled final.target static getty.target static graphical.target static halt.target disabled hibernate.target static hybrid-sleep.target static initrd-fs.target static initrd-root-fs.target static initrd-switch-root.target static initrd.target static kexec.target disabled local-fs-pre.target static local-fs.target static machines.target disabled multi-user.target static network-online.target static network-pre.target static network.target static nfs-client.target disabled nss-lookup.target static nss-user-lookup.target static pacman-database-mon.target static paths.target static poweroff.target disabled prelink-tue.target static printer.target static reboot.target disabled remote-fs-pre.target static remote-fs.target enabled rescue.target disabled rpcbind.target static shutdown.target static sigpwr.target static sleep.target static slices.target static smartcard.target static sockets.target static sound.target static suspend.target static swap.target static sysinit.target static system-update.target static time-sync.target static timers.target static umount.target static fstrim.timer disabled laptop-mode.timer disabled logrotate.timer static man-db.timer static mbsync@.timer enabled pacman-database-mon.timer disabled pacman-keyring.timer disabled prelink-tue.timer disabled shadow.timer static systemd-tmpfiles-clean.timer static updatedb.timer static

312 unit files listed.


cat disabled-systemd-files.org

android debugger - adb.service disabled let libreoffice/emacs find printers - avahi-daemon.service enabled as above - avahi-dnsconfd.service enabled finding block devices - blk-availability.service disabled play bootup sound - canberra-system-bootup.service disabled play reboot sound - canberra-system-shutdown-reboot.service disabled play shutdown sound - canberra-system-shutdown.service disabled store data on computer clusters - ceph-mds@.service disabled store data on computer clusters - ceph-mon@.service disabled store data on computer clusters - ceph-osd@.service disabled agetty manages TTYs - console-getty.service enabled single user login - console-shell.service enabled apply cpu power info - cpupower.service disabled cron scheduling - cronie.service disabled wanted by networkd - dbus-org.freedesktop.network1.service enable wanted by networkd - dbus-org.freedesktop.resolve1.service enable debug early boot - debug-shell.service disabled torrenting - deluge-web.service disabled torrenting - deluged.service disabled wireless get ip address - dhclient@.service disabled wireless get ip addr - dhcpcd.service disabled wireless get ip addr - dhcpcd@.service disabled lvm helper stuff - dm-event.service disabled local mail server for gnus - dovecot.service disabled dependancy for gst plugins bad - fluidsynth.service disabled ftp daemon - ftpd.service disabled my own script - github.service disabled accessing gnunet - gnunet.service disabled virtual console mouse server - gpm.service disabled alternate way of encrypted authentication - gssproxy.service enabled apache web server - httpd.service disabled netctl ethernet stuff - ifplugd@.service disabled ip6 stuff - ip6tables.service disabled an outdated encryption thing ? - krb5-kadmind.service disabled outdated encrypted stuff - krb5-kdc.service disabled outdated encrypted stuff - krb5-kpropd.service disabled let laptop stuff spin down - laptop-mode.service disabled gnome boxes - libvirt-guests.service disabled gnome boxes - libvirtd.service disabled translate tv remote key press into commands - lircd.service disabled translate tv remote key press into commands - lircmd.service disabled laptop mode tools - lmt-poll.service disabled logical volume management - lvm2-lvmetad.service disabled logical volume management - lvm2-monitor.service disabled wifi stuff - netctl-auto@.service disabled wifi stuff - netctl-sleep.service disabled wifi stuff - netctl.service disabled network file system - nfs-blkmap.service disabled network file system - nfs-server.service disabled nginx web server - nginx.service disabled name service cache daemon - nscd.service enabled pacman stuff - pacman_databas-_mon.service disabled firefox sync cache - pdnsd.service disabled make php run fast - php-fpm.service disabled should be Enabled! a faster sendmail alternative - postfix.service disabled should be Enabled! ??? - prelink-tue.service disabled sync remote files - rsyncd.service disabled realtime policy and watchdog daemon - rtkit-daemon.service disabled part of systemd - serial-getty@.service enabled systemd stuff - systemd-bootchart.service enabled systemd stuff - systemd-journal-upload.service enabled systemd stuff - systemd-networkd-wait-online.service enabled systemd stuff - systemd-networkd.service enabled systemd stuff - systemd-nspawn@.service enabled systemd stuff - systemd-resolved.service enabled man udisks - udisks2.service enabled gnome stuff that gdm uses - upower.service disabled change the nice level of programs - verynice.service disabled doing wifi stuff - wpa_supplicant-nl80211@.service disabled doing wifi stuff - wpa_supplicant-wired@.service disabled doing wifi stuff - wpa_supplicant.service disabled doing wifi stuff - wpa_supplicant@.service disabled find printers - avahi-daemon.socket enabled local mail server - dovecot.socket disabled should be Enabled! ???? - git-daemon.socket disabled outdated encryption - krb5-kpropd.socket disabled used with kodi - lircd.socket disabled remote login - rlogin.socket disabled remote procedure calls - rpcbind.socket disabled should be Enabled? stuff - rsh.socket disabled stuff - rsyncd.socket disabled should be enabled - sshd.socket enabled important - systemd-journal-gatewayd.socket enabled important - systemd-journal-remote.socket enabled important - systemd-networkd.socket enabled outdated talking utility - talk.socket disabled outdated communication - telnet.socket disabled enabled - uuidd.socket enabled virtual machine stuff - virtlockd.socket disabled virtual machine stuff - virtlogd.socket disabled force reboot - ctrl-alt-del.target enabled systemd stuff - exit.target enabled systemd stuff - halt.target enabled needed for ctl alt delete - kexec.target enabled systemd stuff - machines.target enabled network filesystem - nfs-client.target disabled should be Enabled! systemd stuff - poweroff.target enabled systemd stuff - reboot.target enabled systemd stuff - rescue.target enabled removed unused blocks on filesytem - fstrim.timer enabled laptop mode tools - laptop-mode.timer disabled pacman-database-mon.timer disabled pacman keyring updater - pacman_keyring.timer enabled prelink-tue.timer disabled


cat disabled-systemd-files.org | grep "enabled"

let libreoffice/emacs find printers - avahi-daemon.service enabled as above - avahi-dnsconfd.service enabled agetty manages TTYs - console-getty.service enabled single user login - console-shell.service enabled alternate way of encrypted authentication - gssproxy.service enabled name service cache daemon - nscd.service enabled part of systemd - serial-getty@.service enabled systemd stuff - systemd-bootchart.service enabled systemd stuff - systemd-journal-upload.service enabled systemd stuff - systemd-networkd-wait-online.service enabled systemd stuff - systemd-networkd.service enabled systemd stuff - systemd-nspawn@.service enabled systemd stuff - systemd-resolved.service enabled man udisks - udisks2.service enabled find printers - avahi-daemon.socket enabled should be enabled - sshd.socket enabled important - systemd-journal-gatewayd.socket enabled important - systemd-journal-remote.socket enabled important - systemd-networkd.socket enabled enabled - uuidd.socket enabled force reboot - ctrl-alt-del.target enabled systemd stuff - exit.target enabled systemd stuff - halt.target enabled needed for ctl alt delete - kexec.target enabled systemd stuff - machines.target enabled systemd stuff - poweroff.target enabled systemd stuff - reboot.target enabled systemd stuff - rescue.target enabled removed unused blocks on filesytem - fstrim.timer enabled pacman keyring updater - pacman_keyring.timer enabled

The complicated way of doing it


cat disabled-systemd-files.org | grep "enabled" | awk '{ print $4 }' -

printers avahi-dnsconfd.service - - encrypted daemon - systemd-bootchart.service systemd-journal-upload.service systemd-networkd-wait-online.service systemd-networkd.service systemd-nspawn@.service systemd-resolved.service udisks2.service avahi-daemon.socket - enabled enabled enabled enabled ctrl-alt-del.target exit.target halt.target alt machines.target poweroff.target reboot.target rescue.target on -


awk '/enabled/ { print $4 }'  disabled-systemd-files.org

printers avahi-dnsconfd.service - - encrypted daemon - systemd-bootchart.service systemd-journal-upload.service systemd-networkd-wait-online.service systemd-networkd.service systemd-nspawn@.service systemd-resolved.service udisks2.service avahi-daemon.socket - enabled enabled enabled enabled ctrl-alt-del.target exit.target halt.target alt machines.target poweroff.target reboot.target rescue.target on -


awk '/enabled/ { print $2 }'  disabled-systemd-files.org

libreoffice/emacs above manages user way service of stuff stuff stuff stuff stuff stuff udisks printers be - - - - reboot stuff stuff for stuff stuff stuff stuff unused keyring

a hodgepodge that works to show all of the services that need be enabled


sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{print $1}' -

avahi-daemon.service avahi-dnsconfd.service console-getty.service console-shell.service gssproxy.service nscd.service serial-getty@.service systemd-bootchart.service systemd-journal-upload.service systemd-networkd-wait-online.service systemd-networkd.service systemd-nspawn@.service systemd-resolved.service udisks2.service avahi-daemon.socket sshd.socket systemd-journal-gatewayd.socket systemd-journal-remote.socket systemd-networkd.socket uuidd.socket ctrl-alt-del.target exit.target halt.target kexec.target machines.target poweroff.target reboot.target rescue.target fstrim.timer pacman_keyring.timer

Put it looks like systemctl does not accept input that way... bummer


su
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{print $1}' - | systemctl enable -


su
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{systemctl enable $1}' -
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{systemctl start $1}' -


su
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{print $1}' - | xargs

avahi-daemon.service avahi-dnsconfd.service console-getty.service console-shell.service gssproxy.service nscd.service serial-getty@.service systemd-bootchart.service systemd-journal-upload.service systemd-networkd-wait-online.service systemd-networkd.service systemd-nspawn@.service systemd-resolved.service udisks2.service avahi-daemon.socket sshd.socket systemd-journal-gatewayd.socket systemd-journal-remote.socket systemd-networkd.socket uuidd.socket ctrl-alt-del.target exit.target halt.target kexec.target machines.target poweroff.target reboot.target rescue.target fstrim.timer pacman_keyring.timer

don't run that command, because it will restart your system


su
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{print $1}' - | xargs -i systemctl enable {}
sed -n '/enabled/  s/^.*- // p ' disabled-systemd-files.org | awk '{print $1}' - | xargs - systemctl start {}

What's our ethernet device name?


ip link | egrep "2:.*n.*:" | awk '{print $2}'

neteth0:


ip link | grep "2" | awk '{print $2}' | sed -n '1 p'

neteth0:

Checking on the status of the ifplugd interface

So this is odd. This command outputs stuff in the terminal, but not here.


su
systemctl | grep -m 1 ifplugd | awk '{print $1}' | xargs systemctl status {}

Redirection

Redirecting input can be of the form [n]

Redirecting output is of the form [n]>[|]word

< means standard input > means standard output

2> means standard error. So

#+BEGIN_SRC sh cat bsah 2> error.txt; #+END_SRC

#+RESULTS:

Will store the error caused by "cat bsah" into the file error.txt.

#+BEGIN_SRC sh cat error.txt #+END_SRC

#+RESULTS:

cat: bsah: No such file or directory

debugging

dmesg | less

cat /var/log/syslog

cat /var/log/messages

TRY out AUTOJUMP it'll remember previous directories and it'll let you jump around in the directory tree

tcpdump lets you look at all of the internet traffic going in and out of your internet chip

randomly play all videos in current directory

find . -type f | shuf | xargs -d "\n" mpv