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Command History
===============
!!                              - Repeat previous command
!!:/s/<search>/<replace>/g      - Repeat previous command with replaced string value
sudo !!							- Repeat previous command with sudo
history                         - Show bash history
!<int>                          - Run a labelled command from history command
!<command>                  a    - Re-run last use of command
<command>:p                     - Print rather than run (e.g. !!:p, to print last run command)
^<search>^<replace>             - Run previous command replacing search with replace (for typos)
<command> !*                    - Use first argument from last command
<command> !:n                   - Use nth argument from last command
<command> !$                    - Use last argument from last command


Shortcuts
===================
Ctrl + r                        - Search history
Up / Down                       - Navigate history
Tab                             - Autocomplete (double tap for matches if more than one)

Ctrl + e                        - Goto end of line
Ctrl + a                        - Goto start of line
Ctrl + d                        - Delete
Ctrl + w                        - Clear word before cursor
Ctrl + u                        - Clear current line
Ctrl + k                        - Clear from cursor
Ctrl + l                        - Clear screen

Ctrl + c                        - Cancel current process


Command Basics
==============
sudo <command>                  - Issue command with root / sudoer privileges
man <command>                   - Manual page for command

<command> &                     - Spin off command as background process
Ctrl + z                        - Suspend current process
bg                              - Send suspended process to background process
fg                              - Bring background process to foreground
alias a="command"               - Set an alias (command shortcut)
nohup <command> &               - Run command in background with hangup signals ignored
<command> | at <HH:MM>          - Run command at specified time

<command1> | <command2>         - Pipe output from command1 to command2
<command1> | xargs <command2>   - Use output from command1 as arguments for command2
<command> > <outfile>           - Redirect stdout to outfile
<command> >> <outfile>          - Redirect stdout to outfile(append rather than overwrite)
<command> < <infile>            - Redirect stdin to command
<command> 2> <outfile>          - Redirect stderr to outfile
<command> 2>&1                  - Redirect stderr to stdout
<command> &> <outfile>          - Redirect stdout and stderr to outfile

<command> <text>{1,2}           - Expands to <command> <text>1 <text>2
<command> <text>{,2}            - Expands to <command> <text> <text>2

clear                           - Clears terminal window


Special Characters
==================
\n                              - New line
\t                              - Tab
*                               - Represent wildcard in arguments (glob)
--                              - Use to escape any further dashes in a command
.                               - Current working directory
..                              - Parent directory
-                               - Last working directory
~                               - Home directory
;                               - Command terminator / seperator


Basic Commands
==============
id                              - Show current user info
whoami                          - Show current username
finger                          - Show system users info
w [<username>]                  - Show logged in users (or specified user) and what they are currently doing
su <user>                       - Switch user
echo <string>                   - Send string to stdout

shutdown -h now                 - Shutdown (halt) now
shutdown -r now                 - Shutdown (restart) now (can just use 'reboot' on some systems
    
env                             - Display current environment variables and values
hostname [<new>]                - Show or with argument set hostname
uname -a                        - Display kernel and OS version

date                            - Show system date / time
time <command>                  - Track time for command to complete
time cat                        - Start stopwatch

top                             - System resource usage statistics
ps                              - Show running processes for current user
ps -e                           - Show running processes for all users
ps -ef                          - Show running processes for all users with expanded information
kill <processId(s)>             - Kill a process
killall <name>                  - Kill a process by name
fuser <file>                    - Find process which is using a file
strace -t <command>             - Trace execution path of command with timestamps
strace -t -p <pid>              - Trace a process with timestamps and optionally write to outfile

df -h                           - Disk usage statisics (all disks)
du -sh                          - Size of current directory / contents
du -hsx * | sort -rh | head -10 - List top 10 size hogs

screen
    - Launch screen (multi terminal manager, identified with ints)
    - Ctrl-a C to create a new screen
    - Crtl-a K to kill current screen
    - Ctrl-a " lists screens
    - Ctrl-a <int> to switch to specified screen
    
pwd                             - Display current working directory
cd <directory>                  - Change current working directory
ls                              - List contents of current working directory
ls -l                           - List contents of current working directory (one per line with more info)
ls -A                           - List contents of current working directory (including hidden files)
ls -lrt                         - List contents of current working directory (+info, in reverse order of last touch)
lsof                            - List open files in current working directory

mkdir <directory>               - Create directory
rmdir <directory>               - Remove directory
rm <file>                       - Delete file
rm -r <directory>               - Delete directory and contents (recursive)
rm -rf <directory>              - Delete directory and contents (recursive), without warnings
cp <file> <destination>         - Copy file
cp -r <directory> <destination> - Copy directory
mv <file> <destination>         - Move (or rename) file or directory
><file>                         - Truncate file

ln <target>                     - Create (hard) symlink to target in current working directory
ln -s <target>                  - Create (symbolic) symlink to target directory in current working directory

touch <file>                    - Create empty file / update last modified timestamp

basename <path>                 - Returns last part of path

mount -a                        - Mount everything in /etc/fstab

find [<path>] <expression>
    - Find file matching expression
    - Optional path points to root of search
    - e.g. find . -name error.html //find all files named error.html in current directory and descendants
    
    
Text Commands
=============
vi <filename>                   - Edit / create file using vi
vim <filename>                  - Edit / create file using vim
nano <filename>                 - Edit / create file using nano
less <file(s)>                  - Display file contents, line by line scroll with Enter, F to trace, Q to quit 
more <file(s)>                  - Display file contents, line by line scroll with Enter (basic / slower version of less)

cat <file(s)>                   - Concatenate files and send to stdout
cat -n <file(s)>                - Concatenate files and send to stdout with line numbers
cat ><file>                     - Redirect stdin to file, Ctrl-C to finish (does not include last line in file)
cat >><file>                    - Same as above but appends rather than overwrites
head [-<int>] <file(s)>         - Show top 10 lines of file (or specify number optionally)       
tail [-<int>] <file(s)>         - Show last 10 lines of file (or specify number optionally), add -F to trace
wc <file(s)>                    - Print byte, word, and line counts for a file (and filename), use -c, -l, -w to return byte, line and work count only (and filename)
nl <file(s)>                    - Add line numbers
tr <set> <set>                  - Replace values from stdin, print to standard out, e.g. tr [da] [bc] would replace d with b and a with c
tr -d <set>                     - Same as above except removes characters without replace
tr -s <set>                     - Same again except removes duplications of characters in set
printf <format> <value>         - Use to format values, full list of modifiers: http://ss64.com/bash/printf.html

for file in `ls`; do sed 's/find/replace/g' $file > /tmp/tmp; mv /tmp/tmp $file; done;
- Replace all matched text in all files in dir

expand -t 4 <filename> > /tmp/tmp; mv /tmp/tmp <filename>
    - Replace tabs with 4 spaces, move file over temp version created in first command

unexpand -t 4 <filename> > /tmp/tmp; mv /tmp/tmp <filename>
    - Opposite of previous commands
    
cut [-b <int|range>] [-c <int|range>] [-d <int|range> [-f <int|range>]] <file(s)>
    - Cut a file into columns for standard out
    - -b option to select a byte position / range
    - -c option to select a character position / range
    - -f option to select a field position / range (where field delimiter specified using -d)
    
sort <file(s)>              - Sort lines from file(s), use -u to only sort unique lines
    
grep <string> <file(s)>
    - Find a string in file(s)
    - Use -i to make case insensitive
    - Use -e for regex as string
    - Use -B to specify number of lines to grab before match
    - Use -A to specify number of lines to grab before match

egrep <pattern> <file(s)>
    - Use regex for matching

zgrep <string> <file(s)>
    - Same as grep but works with compressed files
    
awk <program> <file(s)>
    - Find and replace / sorting / filtering using the awk language
    - <program> 
         '<pattern> { <action> }
         .....' 
    - omit pattern to match every line, omit action to print nothing, omit action and brackets to print whole matched line
    - actions should be terminated with semicolons
    - pattern can use /regEx/, &&, ||, !, ternary operator (a?b:c), range (a,b), before file read (BEGIN), after file read (END)
        - Can match with special operators using ~ e.g. awk '$4 ~ /regex/ {action} //Do action if 4th field matched regex
    - action can be a combination below as well as basic arithmetic:
        - { print $X }
            - if X is 0 then print whole line, else print Xth item on line
        - { print <special>} 
            - NR prints line number
            - NF print number of fields in line
            - FILENAME prints current input filename
        - e.g. $NR is last field
        - Can use literal and escape chars e.g. "This\tis\ttext\twith\ttabs"
        - Variable assignment: var=value;
        - Operators ++, --, +, -, *, /

awk -f <script> <file(s)
    - Same as above only reads program from file
    
awk '!a[$0]++' file
  - Remove duplicate lines
    
egrep "Notice|NOTICE|Strict|STRICT" <file> | sed 's/^.\{22\}//g' | LC_ALL=C sort | uniq -c | sort -rn | head -n 100
  - Find top 100 NOTICE / STRICT errors in a PHP error log

Archiving Commands
==================
tar -cvf <archive> <files>      - Create archive, add z for compression, add --exclude=<glob>before <files> for exclusions
tar -xvf <archive> [<location>] - Expand archive (optionally to destination), add z for decompression
tar -t <archive>                - List file contents of archive

gzip <file>                     - Compress file
gzip -d <file>                  - Decompress file

Networking Commands
===================
wget <address>                  - Fetch file from web address

ssh [<user>]@<host>             - SSH to host as user

scp [[user@]host1:]<file1> [[user@]host2:]<file2>
    - Secure file copy using ssh
    - Use -r flag for copying directories
    
/etc/init.d/network <restart|start|stop>    - Control networking
ifconfig                        - Display and set networking / interface settings
ping <host>                     - Standard icmp ping
traceroute <host>               - Routing info / connection debug
mtr <host>                      - Advanced traceroute / ping
netstat                         - Networking status
netstat -a						- List all listening ports
netstat -tp                     - List services by PID
nslookup <host>                 - DNS lookup
nmap <host>                     - Port scanning

mount -t cifs -o username="[username]",password"[Password]" //[IP]/[folder] [folder]
    - Mount network drive

route -n                        - Show routing
route del <-host|-net> <ip> netmask <netmask>
    - Delete route
route add <-host|-net> <ip> netmask <netmask> gw <ip> dev <interface>
    - Add route
route add <-host|-net> gw <ip> dev <interface>
    - Add default route
    

Permission Commands
===================
chmod <maskOrMod> <file(s)>     - Alter file permissions
chmod -r <maskOrMod> <file(s)>  - Alter file permissions recursively

Modifications in form /(u+g+o+a+)([\+|\-])(r+w+e+)/ where:
    - u is current user
    - g is group
    - o is others
    - a is all
    - + to add permissions
    - - to remove permissions
    - r is read
    - w is write
    - e is execute

Mask values:
    - 4 is read
    - 2 is write
    - 1 is execute
    - e.g. 655 is user (read / write), group (read / execute), others (read / execute)

chgrp <group> <file>            - Change group of a file
useradd -a -G <group> <user>    - Add user to group


Important Files (Vary on system / versions)
===============
~/.bashrc                       - Loaded on new terminal
~/.bash_profile                 - Loaded on new terminal

/dev/null                       - Blackhole (redirect here to null)

/etc/fstab                      - The place for mounting, e.g. //<server>/<folder> <localfolder> cifs auto,username-[username],password=[password],uid=0,gid=500 0 0
/etc/hosts                      - The place for hardcoding DNS entries
/var/log/                       - Log files
/etc/sudoers                    - Sudoers settings
/etc/rc.d/rc.local              - Startup script location
/usr/local/bin                  - Executable scripts (to make available as system wide commands)

/etc/httpd/conf.d/httpd.conf    - Apache config
/etc/apache2/apache2.conf       - Apache2 config
/etc/yum.conf                   - Yum config
/etc/network/interfaces         - Network interfaces config


Aptitude (Package Management for Debian, Ubuntu, Mint...)
========================================================
apt-cache search <package>      - Search apt for package, use ^package$ for exact match, use "package" for description search
apt-cache show <package>        - Show basic package info
apt-cache showpkg <package>     - Show detailed packaged info (including dependancies)
apt-cache depends <package>     - Show dependancies for package
apt-get install <package>       - Install a program / package
apt-get --purge remove <pkg>    - Completely remove a program / package
apt-get autoclean               - Erase old downloaded archive files
apt-get --purge autoremove      - Remove automatically all unused packages
apt-get update                  - Update package index
apt-get upgrade                 - Update installed packages


Yum (Package Management for Red Hat, Fedora...)
===============================================
yum clean all                   - Clean yum cache
yum list <package>              - Search for package
yum install <package>           - Install package
yum downgrade <package>         - Rollback package to previous version
yum check-update                - Check for updates for installed packages
yum update                      - Update installed packages
yum update <package>            - Update package


RPM (Package management)
======================
rpm -ivh <file>         - Install
rpm -Uvh <file>         - Upgrade rpm
rpm -ev <name>          - Remove package


Minicom (Serial Connector)
==========================
minicom                         - Launch
minicom -s                      - Setup
minicom -c <file>               - Launch with output capture file


Apache2 Commands
===============
/etc/init.d/apache2 <restart|start|stop>    - Control web server (apache2)
a2enmod <module>                            - Enable module
a2dismod <module>                           - Disable module
a2ensite <site>                             - Enable site
a2dissite <site>                            - Disable site


Cron
====
crontab -e              - Edit user cronjobs                    
crontab -l              - Display user cronjobs         

/etc/init.d/cron <restart|start|stop>
/etc/init.d/crond <restart|start|stop>
    - Control cron service