Command-line / Shell / Bash Scripting - Snippets, Notes & Whatnot

Crontab.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : Cron-related snippets
#   Tested on Debian 6 ("Squeeze")
#   
#   Sources :
#   https://drupal.org/node/23714
#   http://www.linuxquestions.org/questions/linux-general-1/crontab-every-10-minutes-117651/
#   

#       Edit global config
nano /etc/crontab

#       Per-user alternative
crontab -e

#       Example Contents :

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# m h dom mon dow user  command
17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
#


#       Timing setup notes :
# +---------------- minute (0 - 59)
# |  +------------- hour (0 - 23)
# |  |  +---------- day of month (1 - 31)
# |  |  |  +------- month (1 - 12)
# |  |  |  |  +---- day of week (0 - 6) (Sunday=0)
# |  |  |  |  |
# *  *  *  *  *  user command_to_be_executed

#       Every X minutes, or hours, or whatever, is noted :
#       */X


#       Example Drupal cron - using Drush, every hour at 00 min
0 * * * *  root  cd /var/www/the-drupal-project-folder/ && drush cron

#       Example Drupal cron - using Curl, every hour at 30 min
30 * * * *  root  curl -s http://www.the-drupal-project.com/cron.php

#       Example Drupal cron - using Lynx, every 10 minutes
*/10 * * * *  root /usr/bin/lynx -source http://www.the-drupal-project.com/cron.php



#       Setup a job to execute at reboot
#       (to add to the crontab file)
@reboot /path/to/starter.sh

File-related snippets.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : File-related snippets
#   
#   Tested on Debian, Ubuntu, should work in any Unix system
#   


#---------------------------------------------------------------------------
#       CRUD


#       Create folder
mkdir /path/to/folder

#       Create folder "recursively" (auto creating any missing "intermediate" folders)
mkdir --parent /path/to/folder

#       Create file
echo "File content" > path/to/filename.ext

#       Append content to existing file
#       (auto newline before)
echo "File content" >> path/to/filename.ext

#       Delete file
rm path/to/filename.ext
#       Delete file w/o confirmation prompt
rm path/to/filename.ext --force

#       Delete folder (recursively)
rm path/to/folder -r
#       Delete folder (recursively) w/o confirmation prompt
rm path/to/folder -r --force

#       Read end of file contents (last n lines)
#       NB: replace 10 below for desired nb of lines to display
tail /path/to/file.ext -n10



#---------------------------------------------------------------------------
#       Search


#       Look for text in files
#       NB: "example" is regex
find /path/to/folder -type f -exec grep "example" {} +

#       Match whole word
grep "^\W*example" path/to/file | tr -s " "

#       List matching folders (with slash)
find . -type d -wholename "*my/path/to*"

#       List *.jpg files (recursively)
find . -name "*.jpg"

#       Delete "found" files
find . -depth -type f -name "*.jpg" -exec rm -f {} +

#       List folders named 'images' (recursively)
find . -type d -name "*\images"

#       Delete "found" folders
find . -depth -type d -name "*\images" -exec rm -rf {} +



#---------------------------------------------------------------------------
#       Replace


#       Search / replace (regex) inside a file
#       -> "example" will be replaced by "foobar"
sed -e 's,example,foobar,g' -i /path/to/filename

#       Idem, but creating a backup filename.bak before modifying the file
#       (notice the param "-i.bak")
sed -e 's,example,foobar,g' -i.bak /path/to/filename



#---------------------------------------------------------------------------
#       Compress


#       Create tar/gzip archive
tar czf filename.tgz example_filename.ext
tar czf filename.tgz example_dirname/

#       Compress excluding a folder
#       NB: no trailing slashes in excluded folders
tar czf --exclude=www/sites/default/files filename.tgz www/

#       Compress excluding multiple folders
#       NB: no trailing slashes in excluded folders
#       @see http://stackoverflow.com/questions/984204/shell-command-to-tar-directory-excluding-certain-files-folders
tar czf --exclude='/path/to/excluded/folder/a' --exclude='/path/to/excluded/folder/b' filename.tgz /path/to/compress/

#       Compress excluding files larger than 1024k
find . -type f -size -1024k | tar -cz -f filename.tgz -T -

#       Decompress (tar/gzip)
tar xzf filename.tgz
tar xzf filename.tgz destination_dir/



#---------------------------------------------------------------------------
#       Mount


#       Mounting local (LAN) shared filesystem in Linux
#       @see http://stackoverflow.com/questions/5070545/php-read-file-contents-of-network-share-file
#       @see http://craig.mayhew.io/blog/2010/12/mounting-a-windows-share-on-linux/
mount -t cifs //192.168.xxx.xxx/path/to/share /path/to/dirtomount -o user=USERNAME,password=PASSWORD

fixperms-d6.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Drupal 6 Permissions
#   
#   Sources :
#   https://drupal.org/node/244924
#   

VERSION="1.0-dev"
SCRIPT_NAME="$(basename ${0})"


##
#   Usage info
#
function usage {
  echo "Set ownership & permissions for files & folders (for Drupal 6) v${VERSION}
Usage :
  ./${SCRIPT_NAME} [ owner ] [ group ] [ path ]
"
  exit 1
}

#       Param 1 : owner
#       default : current user
P_OWNER=${1}
if [ -z "${1}" ]; then
    P_OWNER="$USER"
fi

#       Param 2 : group
#       default : www-data
P_GROUP=${2}
if [ -z "${2}" ]; then
    P_GROUP="www-data"
fi

#       Param 3 : path
#       default : .
P_PATH=${3}
if [ -z "${3}" ]; then
    P_PATH="."
fi

#       debug ok 2014/06/20 16:06:18
#echo "debug param 1 = ${P_OWNER}"
#echo "debug param 2 = ${P_GROUP}"
#echo "debug param 3 = ${P_PATH}"


#       Current dir (or replace '.' below)
cd $P_PATH

#       Owner/group
chown $P_OWNER:$P_GROUP . -R

#       Non-writeable files
find . -type f -exec chmod 640 {} +

#       Non-writeable dirs
find . -type d -exec chmod 750 {} +

#       Writeable files (Drupal6 example dir structure)
find . -type f -wholename "*sites/default/files*" -exec chmod 660 {} +
#       (Boost file cache)
find . -type f -wholename "*cache/normal*" -exec chmod 660 {} +
find . -type f -wholename "*cache/perm*" -exec chmod 660 {} +

#       Writeable dirs (Drupal6 example dir structure)
find . -type d -wholename "*sites/default/files*" -exec chmod 770 {} +
#       (Boost file cache)
find . -type d -wholename "*cache/normal*" -exec chmod 770 {} +
find . -type d -wholename "*cache/perm*" -exec chmod 770 {} +

fixperms-d7.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Drupal 7 Permissions
#   
#   Sources :
#   https://drupal.org/node/244924
#   

VERSION="1.0-dev"
SCRIPT_NAME="$(basename ${0})"


##
#   Usage info
#
function usage {
  echo "Set ownership & permissions for files & folders for Drupal 7 v${VERSION}
Usage :
  ./${SCRIPT_NAME} [ owner ] [ group ] [ path ]
"
  exit 1
}

#       Param 1 : owner
#       default : current user
P_OWNER=${1}
if [ -z "${1}" ]; then
    P_OWNER="$USER"
fi

#       Param 2 : group
#       default : www-data
P_GROUP=${2}
if [ -z "${2}" ]; then
    P_GROUP="www-data"
fi

#       Param 3 : path
#       default : .
P_PATH=${3}
if [ -z "${3}" ]; then
    P_PATH="."
fi

#       debug ok 2014/06/19 04:10:10
#echo "debug param 1 = ${P_OWNER}"
#echo "debug param 2 = ${P_GROUP}"
#echo "debug param 3 = ${P_PATH}"


#       Current dir (or replace '.' below)
cd $P_PATH

#       Owner/group
chown $P_OWNER:$P_GROUP . -R

#       Non-writeable files
find . -type f -exec chmod 640 {} +

#       Non-writeable dirs
find . -type d -exec chmod 750 {} +

#       Writeable files (Drupal7 example dir structure)
find . -type f -wholename "*sites/default/files*" -exec chmod 660 {} +
find . -type f -wholename "*sites/default/tmp*" -exec chmod 660 {} +
find . -type f -wholename "*sites/default/private*" -exec chmod 660 {} +

#       Writeable dirs (Drupal7 example dir structure)
find . -type d -wholename "*sites/default/files*" -exec chmod 770 {} +
find . -type d -wholename "*sites/default/tmp*" -exec chmod 770 {} +
find . -type d -wholename "*sites/default/private*" -exec chmod 770 {} +

htaccess-htpasswd.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : Manage Apache "htaccess & htpasswd" - based access restriction
#   Tested 2013/12/04 13:18:49 on Debian 6 ("Squeeze")
#   


#------------------------------------------------------------------------------------------
#       .htaccess or Apache settings contents

Order allow,deny
Allow from all
Options None

AuthUserFile /path/to/htpasswd-file
AuthName "Title of Authentication"
AuthType Basic
require valid-user



#------------------------------------------------------------------------------------------
#       .htpasswd creation

#       Syntax :
htpasswd -bc /path/to/htpasswd-file UserName UserPassword



#------------------------------------------------------------------------------------------
#       Alternative : only apply for an IP
#       Note : using 127.0.0.1 or "localhost" does NOT work :(
#       @see http://stackoverflow.com/questions/8854909/apache-authentication-except-localhost

# permit by USER || IP
Satisfy any
# USER
AuthUserFile /var/www/munin/.htpasswd
AuthGroupFile /dev/null
AuthName "Password Protected Area"
AuthType Basic
require valid-user
# IP
order deny,allow
deny from all
allow from 123.123.123.123



#------------------------------------------------------------------------------------------
#       Reference

#       htpasswd command :
#htpasswd [-cmdpsD] passwordfile username
#htpasswd -b[cmdpsD] passwordfile username password
#htpasswd -n[mdps] username
#htpasswd -nb[mdps] username password
# -c  Create a new file.
# -n  Don't update file; display results on stdout.
# -m  Force MD5 encryption of the password.
# -d  Force CRYPT encryption of the password (default).
# -p  Do not encrypt the password (plaintext).
# -s  Force SHA encryption of the password.
# -b  Use the password from the command line rather than prompting for it.
# -D  Delete the specified user.

list_users.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : List all normal user and system accounts in the system.
#   Tested on RHEL / Debian Linux
#   
#   Author: Vivek Gite <www.cyberciti.biz>, under GPL v2.0+
#   
#   Sources :
#   http://www.cyberciti.biz/faq/linux-list-users-command/
#

_l="/etc/login.defs"
_p="/etc/passwd"

## get mini UID limit ##
l=$(grep "^UID_MIN" $_l)

## get max UID limit ##
l1=$(grep "^UID_MAX" $_l)

## use awk to print if UID >= $MIN and UID <= $MAX and shell is not /sbin/nologin   ##
echo "----------[ Normal User Accounts ]---------------"
awk -F':' -v "min=${l##UID_MIN}" -v "max=${l1##UID_MAX}" '{ if ( $3 >= min && $3 <= max  && $7 != "/sbin/nologin" ) print $0 }' "$_p"

echo ""
echo "----------[ System User Accounts ]---------------"
awk -F':' -v "min=${l##UID_MIN}" -v "max=${l1##UID_MAX}" '{ if ( !($3 >= min && $3 <= max  && $7 != "/sbin/nologin")) print $0 }' "$_p"

Misc.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : Miscellaneous
#   
#   Tested in :
#   Debian 7 "wheezy"
#   Ubuntu 14.04 LTS "trusty"
#   
#   Sources :
#   http://serverfault.com/questions/490825/how-to-set-the-domain-name-on-gnu-linux
#   http://askubuntu.com/questions/151941/how-can-you-completely-remove-a-package
#   http://askubuntu.com/questions/254826/how-to-force-a-clock-update-using-ntp
#   


#---------------------------------------------------------------------
#       Get current linux version

lsb_release -a


#---------------------------------------------------------------------
#       Change server's hostname
#       (installed domain name)

#       (content of this file is the domain)
nano /etc/hostname

#       Activate hostname
hostname -F /etc/hostname

#       Add domain name and address to the server
#       (in this file, replace old domain with desired one)
nano /etc/hosts


#---------------------------------------------------------------------
#       List all active sockets / connexions (only servers)

netstat -l


#---------------------------------------------------------------------
#       Remove package

#       Along with with non-manual dependencies
#       (will not remove non-systemwide configuration files)
#       @see http://askubuntu.com/questions/151941/how-can-you-completely-remove-a-package
apt-get --purge autoremove


#---------------------------------------------------------------------
#       Force time update

ntpdate -sb time.nist.gov

Permissions.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Unix Permissions Basics & snippets
#   (Command-line / Shell / Bash)
#   
#   Tested on :
#   Debian 7 "wheezy"
#   Unbuntu 14.04 "trusty"
#   
#   Sources :
#   http://www.tldp.org/LDP/abs/html/invoking.html
#   http://www.yolinux.com/TUTORIALS/LinuxTutorialManagingGroups.html
#   https://www.digitalocean.com/community/tutorials/linux-permissions-basics-and-how-to-use-umask-on-a-vps
#   


#----------------------------------------------------------------------------------------
#       Disambiguation


#       User name   :   human-readable name of a Linux user
#           OR      :   "machine" name of a Linux user (usually, a lowercase version of the human-readable name), also = user login
#       User ID     :   user login
#           OR      :   unique numerical reference to the user
#       (same goes for group id and group name)



#----------------------------------------------------------------------------------------
#       Explanations


#       On Linux :
#       1. Each file is owned by exactly one user and one group.
#       2. Users may belong to several groups, and are automatically assigned a User Private Group (UPG)
#           which is a unique group of the same name as the user.
#       3. Configuring services/programs to operate AS a distinct user allows to control their permissions.
#       4. Permission to read a directory also requires execution permission.

#       Notations :
#       Description = Abreviation = Octal Code
Read                        = r     = 4
Write                       = w     = 2
Execute                     = x     = 1
Read and Execute            = rx    = 5
Read and Write              = rw    = 6
Read, Write and Execute     = rwx   = 7



#----------------------------------------------------------------------------------------
#       Utilities


#       List users
cat /etc/passwd

#       List groups
groups

#       List groups
groups user_id

#       Set ownership
chown user_id:group_id [-R]

#       Set permissions
chmod [octal] file/or/directory [-R]

#       Change specific permissions
#       @see http://man.yolinux.com/cgi-bin/man2html?cgi_command=chmod
chmod [ugoa][+-=][rwxXst] file/or/directory [-R]



#----------------------------------------------------------------------------------------
#       Snippets


#       Give everyone read/execute permission
chmod 555 my_filename
chmod +rx my_filename

#       Give just the script owner read/execute permission
chmod u+rx my_filename

#       Execute for all files in current dir & subdirs
find . -type f -exec chmod 640 {} +

#       Restrict by path (matching by pattern)
find . -type f -wholename "*sites/default/files*" -exec chmod 660 {} +

#       Execute for all dirs in current dir & subdirs
find . -type d -exec chmod 750 {} +

php-fpm-fixperms-d7.script.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Drupal 7 Permissions - PHP-FPM nginx Ajenti setup
#   
#   Sources :
#   https://drupal.org/node/244924
#   

VERSION="1.0-dev"
SCRIPT_NAME="$(basename ${0})"


##
#   Usage info
#
function usage {
  echo "Set ownership & permissions for files & folders for Drupal 7 v${VERSION}
Usage :
  ./${SCRIPT_NAME} [ owner ] [ group ] [ path ]
"
  exit 1
}

#       Param 1 : owner
#       default : current user
P_OWNER=${1}
if [ -z "${1}" ]; then
    P_OWNER="$USER"
fi

#       Param 2 : group
#       default : www-data
P_GROUP=${2}
if [ -z "${2}" ]; then
    P_GROUP="www-data"
fi

#       Param 3 : path
#       default : .
P_PATH=${3}
if [ -z "${3}" ]; then
    P_PATH="."
fi

#       debug ok 2014/06/19 04:10:10
#echo "debug param 1 = ${P_OWNER}"
#echo "debug param 2 = ${P_GROUP}"
#echo "debug param 3 = ${P_PATH}"


#       Current dir (or replace '.' below)
cd $P_PATH

#       Owner/group
chown $P_OWNER:$P_GROUP . -R

#       Non-writeable files
find . -type f -exec chmod 750 {} +

#       Non-writeable dirs
find . -type d -exec chmod 750 {} +

#       Writeable files (Drupal7 example dir structure)
find . -type f -wholename "*sites/default/files*" -exec chmod 660 {} +
find . -type f -wholename "*sites/default/tmp*" -exec chmod 660 {} +
find . -type f -wholename "*sites/default/private*" -exec chmod 660 {} +

#       Writeable dirs (Drupal7 example dir structure)
find . -type d -wholename "*sites/default/files*" -exec chmod 770 {} +
find . -type d -wholename "*sites/default/tmp*" -exec chmod 770 {} +
find . -type d -wholename "*sites/default/private*" -exec chmod 770 {} +

PostgreSQL snippets.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : PostgreSQL 8.4.17
#   
#   Tested on Debian 6 ("Squeeze")
#   
#   Sources :
#   http://www.postgresql.org/docs/8.4/static/libpq-pgpass.html
#   http://stackoverflow.com/questions/1348126/modify-owner-on-all-tables-simultaneously-in-postgresql
#   http://stackoverflow.com/questions/13358973/how-to-run-a-sql-command-from-a-bash-variable-via-ssh-and-psql
#   http://stackoverflow.com/questions/12232640/in-postgresql-whats-the-difference-a-database-and-a-relation-error-rela
#   http://stackoverflow.com/questions/11599533/postgresql-8-4-grant-dml-privileges-on-all-tables-to-a-role
#   

#-----------------------------------------------------------------------------------
#       Prepare server for using commands like "pg_dump",
#       without being prompted for a password every time.
#       @see http://www.postgresql.org/docs/8.4/static/libpq-pgpass.html
#       format : "hostname:port:database:username:password"
#       default port is 5432
#       -> ex :

echo 'localhost:5432:DB_NAME_A:USER_NAME_A:PASSWORD_A
localhost:5432:DB_NAME_B:USER_NAME_B:PASSWORD_B
localhost:5432:DB_NAME_C:USER_NAME_C:PASSWORD_C
' > ~/.pgpass
chmod 0600 ~/.pgpass


#-----------------------------------------------------------------------------------
#       Make DB Dump (tgz compressed)

#       @todo auto datestamp in filename - e.g. MY_FILE_NAME-$(date +%F-%H-%M-%S).sql.tar
pg_dump -i -U USER_NAME -h localhost -F t DB_NAME > MY_FILE_NAME.sql.tar
tar czf MY_FILE_NAME.sql.tar.gz MY_FILE_NAME.sql.tar
rm MY_FILE_NAME.sql.tar


#-----------------------------------------------------------------------------------
#       Restore DB Dump (tgz compressed)

tar xzf MY_FILE_NAME.sql.tar.tgz
pg_restore --username "USER_NAME" --dbname "DB_NAME" -h localhost --verbose --ignore-version MY_FILE_NAME.sql.tar
rm MY_FILE_NAME.sql.tar


#-----------------------------------------------------------------------------------
#       Restore PgSQL Dump (NOT compressed : "plain" restore)

#       Ex. when logged in as root
su - postgres
psql DB_NAME -f MY_FILE_NAME.sql

#       Setting schema owner
#       (if inside a terminal pgsql, exit first by typing "\q", or just paste the query)
#       @see http://stackoverflow.com/questions/13358973/how-to-run-a-sql-command-from-a-bash-variable-via-ssh-and-psql
psql DB_NAME -c "ALTER SCHEMA my_shema_name OWNER TO my_owner_name"


#-----------------------------------------------------------------------------------
#       Fixing table owner problems

#       Ex. when logged in as root
#       @see http://stackoverflow.com/questions/1348126/modify-owner-on-all-tables-simultaneously-in-postgresql
su - postgres
for tbl in `psql -qAt -c "select tablename from pg_tables where schemaname = 'SCHEMA_NAME';" DB_NAME` ; do  psql -c "alter table SCHEMA_NAME.$tbl owner to OWNER_NAME" DB_NAME ; done

screen.sh

#!/bin/bash
# -*- coding: UTF8 -*-

##
#   Command-line / Shell / Bash - snippets : the "screen" command
#   Tested on Debian 6 ("Squeeze")
#   
#   Contents
#       1. Concept
#       2. Usage
#       3. Documentation / Reference (help)
#   
#   Sources :
#   http://www.thegeekstuff.com/2010/07/screen-command-examples/
#

#----------------------------------------------------
#   1. Concept

#   "screen" is to the command-line what tabs are to web browsers.
#   Feels like using wormholes to "encapsulate" several terminals from the one currently in use.
#   Essentially used for parallel execution / mutli-tasking inside a single terminal.
#   Like "nohup", but allowing to navigate from one "screened" command to another (like tabs).


#----------------------------------------------------
#   2. Usage

#   Send a command in a screen
#   "open new tab"
screen unix-command-to-be-executed
#   same as
screen ./unix-shell-script-to-be-executed

#   List screens running - get their id
#   "list opened tabs"
screen -ls

#   Go back 'home'
#   "switch tab"
#   CTRL+A followed by d

#   Kill a screened process (detach)
#   "close tab"
screen -d <pid>.<tty>.<host>

#   Go to a screened process (reattach)
#   "switch tab"
screen -r <pid>.<tty>.<host>


#----------------------------------------------------
#   3. Documentation / Reference (help)

screen -h

#Use: screen [-opts] [cmd [args]]
# or: screen -r [host.tty]

#Options:
#-a            Force all capabilities into each window's termcap.
#-A -[r|R]     Adapt all windows to the new display width & height.
#-c file       Read configuration file instead of '.screenrc'.
#-d (-r)       Detach the elsewhere running screen (and reattach here).
#-dmS name     Start as daemon: Screen session in detached mode.
#-D (-r)       Detach and logout remote (and reattach here).
#-D -RR        Do whatever is needed to get a screen session.
#-e xy         Change command characters.
#-f            Flow control on, -fn = off, -fa = auto.
#-h lines      Set the size of the scrollback history buffer.
#-i            Interrupt output sooner when flow control is on.
#-l            Login mode on (update /var/run/utmp), -ln = off.
#-list         or -ls. Do nothing, just list our SockDir.
#-L            Turn on output logging.
#-m            ignore $STY variable, do create a new screen session.
#-O            Choose optimal output rather than exact vt100 emulation.
#-p window     Preselect the named window if it exists.
#-q            Quiet startup. Exits with non-zero return code if unsuccessful.
#-r            Reattach to a detached screen process.
#-R            Reattach if possible, otherwise start a new session.
#-s shell      Shell to execute rather than $SHELL.
#-S sockname   Name this session <pid>.sockname instead of <pid>.<tty>.<host>.
#-t title      Set title. (window's name).
#-T term       Use term as $TERM for windows, rather than "screen".
#-U            Tell screen to use UTF-8 encoding.
#-v            Print "Screen version 4.00.03jw4 (FAU) 2-May-06".
#-wipe         Do nothing, just clean up SockDir.
#-x            Attach to a not detached screen. (Multi display mode).
#-X            Execute <cmd> as a screen command in the specified session.

shell_keyboard_shortcuts.txt

Control characters are not normally useful inside a script.

Ctl-A

Moves cursor to beginning of line of text (on the command-line).

Ctl-B

Backspace (nondestructive).


Ctl-C

Break. Terminate a foreground job.


Ctl-D

Log out from a shell (similar to exit).

EOF (end-of-file). This also terminates input from stdin.

When typing text on the console or in an xterm window, Ctl-D erases the character under the cursor. When there are no characters present, Ctl-D logs out of the session, as expected. In an xterm window, this has the effect of closing the window.

Ctl-E

Moves cursor to end of line of text (on the command-line).

Ctl-F

Moves cursor forward one character position (on the command-line).


Ctl-G

BEL. On some old-time teletype terminals, this would actually ring a bell. In an xterm it might beep.


Ctl-H

Rubout (destructive backspace). Erases characters the cursor backs over while backspacing.

#!/bin/bash
# Embedding Ctl-H in a string.

a="^H^H"                  # Two Ctl-H's -- backspaces
                          # ctl-V ctl-H, using vi/vim
echo "abcdef"             # abcdef
echo
echo -n "abcdef$a "       # abcd f
#  Space at end  ^              ^  Backspaces twice.
echo
echo -n "abcdef$a"        # abcdef
#  No space at end               ^ Doesn't backspace (why?).
                          # Results may not be quite as expected.
echo; echo

# Constantin Hagemeier suggests trying:
# a=$'\010\010'
# a=$'\b\b'
# a=$'\x08\x08'
# But, this does not change the results.

########################################

# Now, try this.

rubout="^H^H^H^H^H"       # 5 x Ctl-H.

echo -n "12345678"
sleep 2
echo -n "$rubout"
sleep 2
Ctl-I

Horizontal tab.


Ctl-J

Newline (line feed). In a script, may also be expressed in octal notation -- '\012' or in hexadecimal -- '\x0a'.

Ctl-K

Vertical tab.

When typing text on the console or in an xterm window, Ctl-K erases from the character under the cursor to end of line. Within a script, Ctl-K may behave differently, as in Lee Lee Maschmeyer's example, below.

Ctl-L

Formfeed (clear the terminal screen). In a terminal, this has the same effect as the clear command. When sent to a printer, a Ctl-L causes an advance to end of the paper sheet.


Ctl-M

Carriage return.

#!/bin/bash
# Thank you, Lee Maschmeyer, for this example.

read -n 1 -s -p \
$'Control-M leaves cursor at beginning of this line. Press Enter. \x0d'
           # Of course, '0d' is the hex equivalent of Control-M.
echo >&2   #  The '-s' makes anything typed silent,
           #+ so it is necessary to go to new line explicitly.

read -n 1 -s -p $'Control-J leaves cursor on next line. \x0a'
           #  '0a' is the hex equivalent of Control-J, linefeed.
echo >&2

###

read -n 1 -s -p $'And Control-K\x0bgoes straight down.'
echo >&2   #  Control-K is vertical tab.

# A better example of the effect of a vertical tab is:

var=$'\x0aThis is the bottom line\x0bThis is the top line\x0a'
echo "$var"
#  This works the same way as the above example. However:
echo "$var" | col
#  This causes the right end of the line to be higher than the left end.
#  It also explains why we started and ended with a line feed --
#+ to avoid a garbled screen.

# As Lee Maschmeyer explains:
# --------------------------
#  In the [first vertical tab example] . . . the vertical tab
#+ makes the printing go straight down without a carriage return.
#  This is true only on devices, such as the Linux console,
#+ that can't go "backward."
#  The real purpose of VT is to go straight UP, not down.
#  It can be used to print superscripts on a printer.
#  The col utility can be used to emulate the proper behavior of VT.

exit 0
Ctl-N

Erases a line of text recalled from history buffer [8] (on the command-line).

Ctl-O

Issues a newline (on the command-line).

Ctl-P

Recalls last command from history buffer (on the command-line).

Ctl-Q

Resume (XON).

This resumes stdin in a terminal.

Ctl-R

Backwards search for text in history buffer (on the command-line).

Ctl-S

Suspend (XOFF).

This freezes stdin in a terminal. (Use Ctl-Q to restore input.)

Ctl-T

Reverses the position of the character the cursor is on with the previous character (on the command-line).

Ctl-U

Erase a line of input, from the cursor backward to beginning of line. In some settings, Ctl-U erases the entire line of input, regardless of cursor position.

Ctl-V

When inputting text, Ctl-V permits inserting control characters. For example, the following two are equivalent:
echo -e '\x0a'
echo <Ctl-V><Ctl-J>

Ctl-V is primarily useful from within a text editor.

Ctl-W

When typing text on the console or in an xterm window, Ctl-W erases from the character under the cursor backwards to the first instance of whitespace. In some settings, Ctl-W erases backwards to first non-alphanumeric character.

Ctl-X

In certain word processing programs, Cuts highlighted text and copies to clipboard.

Ctl-Y

Pastes back text previously erased (with Ctl-U or Ctl-W).

Ctl-Z

Pauses a foreground job.

Substitute operation in certain word processing applications.

EOF (end-of-file) character in the MSDOS filesystem.