#!/bin/bash

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# SHORTCUTS

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CTRL+A # move to beginning of line

CTRL+B # moves backward one character

CTRL+C # halts the current command

CTRL+D # deletes one character backward or logs out of current session, similar to exit

CTRL+E # moves to end of line

CTRL+F # moves forward one character

CTRL+G # aborts the current editing command and ring the terminal bell

CTRL+J # same as RETURN

CTRL+K # deletes (kill) forward to end of line

CTRL+L # clears screen and redisplay the line

CTRL+M # same as RETURN

CTRL+N # next line in command history

CTRL+O # same as RETURN, then displays next line in history file

CTRL+P # previous line in command history

CTRL+R # searches backward

CTRL+S # searches forward

CTRL+T # transposes two characters

CTRL+U # kills backward from point to the beginning of line

CTRL+V # makes the next character typed verbatim

CTRL+W # kills the word behind the cursor

CTRL+X # lists the possible filename completions of the current word

CTRL+Y # retrieves (yank) last item killed

CTRL+Z # stops the current command, resume with fg in the foreground or bg in the background

ALT+B # moves backward one word

ALT+D # deletes next word

ALT+F # moves forward one word

DELETE # deletes one character backward

!! # repeats the last command

exit # logs out of current session

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# BASH BASICS

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env # displays all environment variables

echo $SHELL # displays the shell you're using

echo $BASH_VERSION # displays bash version

bash # if you want to use bash (type exit to go back to your previously opened shell)

whereis bash # finds out where bash is on your system

which bash # finds out which program is executed as 'bash' (default: /bin/bash, can change across environments)

clear # clears content on window (hide displayed lines)

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# FILE COMMANDS

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ls # lists your files in current directory, ls <dir> to print files in a specific directory

ls -l # lists your files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified

ls -a # lists all files, including hidden files (name beginning with '.')

ln -s <filename> <link> # creates symbolic link to file

touch <filename> # creates or updates (edit) your file

cat <filename> # prints file raw content (will not be interpreted)

any_command > <filename> # '>' is used to perform redirections, it will set any_command's stdout to file instead of "real stdout" (generally /dev/stdout)

more <filename> # shows the first part of a file (move with space and type q to quit)

head <filename> # outputs the first lines of file (default: 10 lines)

tail <filename> # outputs the last lines of file (useful with -f option) (default: 10 lines)

vim <filename> # opens a file in VIM (VI iMproved) text editor, will create it if it doesn't exist

mv <filename1> <dest> # moves a file to destination, behavior will change based on 'dest' type (dir: file is placed into dir; file: file will replace dest (tip: useful for renaming))

cp <filename1> <dest> # copies a file

rm <filename> # removes a file

diff <filename1> <filename2> # compares files, and shows where they differ

wc <filename> # tells you how many lines, words and characters there are in a file. Use -lwc (lines, word, character) to ouput only 1 of those informations

chmod -options <filename> # lets you change the read, write, and execute permissions on your files (more infos: SUID, GUID)

gzip <filename> # compresses files using gzip algorithm

gunzip <filename> # uncompresses files compressed by gzip

gzcat <filename> # lets you look at gzipped file without actually having to gunzip it

lpr <filename> # prints the file

lpq # checks out the printer queue

lprm <jobnumber> # removes something from the printer queue

genscript # converts plain text files into postscript for printing and gives you some options for formatting

dvips <filename> # prints .dvi files (i.e. files produced by LaTeX)

grep <pattern> <filenames> # looks for the string in the files

grep -r <pattern> <dir> # search recursively for pattern in directory

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# DIRECTORY COMMANDS

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mkdir <dirname> # makes a new directory

cd # changes to home

cd <dirname> # changes directory

pwd # tells you where you currently are

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# SSH, SYSTEM INFO & NETWORK COMMANDS

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ssh user@host # connects to host as user

ssh -p <port> user@host # connects to host on specified port as user

ssh-copy-id user@host # adds your ssh key to host for user to enable a keyed or passwordless login

whoami # returns your username

passwd # lets you change your password

quota -v # shows what your disk quota is

date # shows the current date and time

cal # shows the month's calendar

uptime # shows current uptime

w # displays whois online

finger <user> # displays information about user

uname -a # shows kernel information

man <command> # shows the manual for specified command

df # shows disk usage

du <filename> # shows the disk usage of the files and directories in filename (du -s give only a total)

last <yourUsername> # lists your last logins

ps -u yourusername # lists your processes

kill <PID> # kills the processes with the ID you gave

killall <processname> # kill all processes with the name

top # displays your currently active processes

bg # lists stopped or background jobs ; resume a stopped job in the background

fg # brings the most recent job in the foreground

fg <job> # brings job to the foreground

ping <host> # pings host and outputs results

whois <domain> # gets whois information for domain

dig <domain> # gets DNS information for domain

dig -x <host> # reverses lookup host

wget <file> # downloads file

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# VARIABLES

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varname=value # defines a variable

varname=value command # defines a variable to be in the environment of a particular subprocess

echo $varname # checks a variable's value

echo $$ # prints process ID of the current shell

echo $! # prints process ID of the most recently invoked background job

echo $? # displays the exit status of the last command

export VARNAME=value # defines an environment variable (will be available in subprocesses)

array[0]=valA # how to define an array

array[1]=valB

array[2]=valC

array=([2]=valC [0]=valA [1]=valB) # another way

array=(valA valB valC) # and another

${array[i]} # displays array's value for this index. If no index is supplied, array element 0 is assumed

${#array[i]} # to find out the length of any element in the array

${#array[@]} # to find out how many values there are in the array

declare -a # the variables are treaded as arrays

declare -f # uses function names only

declare -F # displays function names without definitions

declare -i # the variables are treaded as integers

declare -r # makes the variables read-only

declare -x # marks the variables for export via the environment

${varname:-word} # if varname exists and isn't null, return its value; otherwise return word

${varname:=word} # if varname exists and isn't null, return its value; otherwise set it word and then return its value

${varname:?message} # if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script

${varname:+word} # if varname exists and isn't null, return word; otherwise return null

${varname:offset:length} # performs substring expansion. It returns the substring of $varname starting at offset and up to length characters

${variable#pattern} # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest

${variable##pattern} # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest

${variable%pattern} # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest

${variable%%pattern} # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest

${variable/pattern/string} # the longest match to pattern in variable is replaced by string. Only the first match is replaced

${variable//pattern/string} # the longest match to pattern in variable is replaced by string. All matches are replaced

${#varname} # returns the length of the value of the variable as a character string

*(patternlist) # matches zero or more occurrences of the given patterns

+(patternlist) # matches one or more occurrences of the given patterns

?(patternlist) # matches zero or one occurrence of the given patterns

@(patternlist) # matches exactly one of the given patterns

!(patternlist) # matches anything except one of the given patterns

$(UNIX command) # command substitution: runs the command and returns standard output

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# FUNCTIONS

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# The function refers to passed arguments by position (as if they were positional parameters), that is, $1, $2, and so forth.

# $@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters.

function functname() {

shell commands

}

unset -f functname # deletes a function definition

declare -f # displays all defined functions in your login session

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# FLOW CONTROLS

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statement1 && statement2 # and operator

statement1 || statement2 # or operator

-a # and operator inside a test conditional expression

-o # or operator inside a test conditional expression

# STRINGS

str1 = str2 # str1 matches str2

str1 != str2 # str1 does not match str2

str1 < str2 # str1 is less than str2 (alphabetically)

str1 > str2 # str1 is greater than str2 (alphabetically)

-n str1 # str1 is not null (has length greater than 0)

-z str1 # str1 is null (has length 0)

# FILES

-a file # file exists

-d file # file exists and is a directory

-e file # file exists; same -a

-f file # file exists and is a regular file (i.e., not a directory or other special type of file)

-r file # you have read permission

-s file # file exists and is not empty

-w file # your have write permission

-x file # you have execute permission on file, or directory search permission if it is a directory

-N file # file was modified since it was last read

-O file # you own file

-G file # file's group ID matches yours (or one of yours, if you are in multiple groups)

file1 -nt file2 # file1 is newer than file2

file1 -ot file2 # file1 is older than file2

# NUMBERS

-lt # less than

-le # less than or equal

-eq # equal

-ge # greater than or equal

-gt # greater than

-ne # not equal

if condition

then

statements

[elif condition

then statements...]

[else

statements]

fi

for x in {1..10}

do

statements

done

for name [in list]

do

statements that can use $name

done

for (( initialisation ; ending condition ; update ))

do

statements...

done

case expression in

pattern1 )

statements ;;

pattern2 )

statements ;;

esac

select name [in list]

do

statements that can use $name

done

while condition; do

statements

done

until condition; do

statements

done

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# COMMAND-LINE PROCESSING CYCLE

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# The default order for command lookup is functions, followed by built-ins, with scripts and executables last.

# There are three built-ins that you can use to override this order: `command`, `builtin` and `enable`.

command # removes alias and function lookup. Only built-ins and commands found in the search path are executed

builtin # looks up only built-in commands, ignoring functions and commands found in PATH

enable # enables and disables shell built-ins

eval # takes arguments and run them through the command-line processing steps all over again

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# INPUT/OUTPUT REDIRECTORS

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cmd1|cmd2 # pipe; takes standard output of cmd1 as standard input to cmd2

< file # takes standard input from file

> file # directs standard output to file

>> file # directs standard output to file; append to file if it already exists

>|file # forces standard output to file even if noclobber is set

n>|file # forces output to file from file descriptor n even if noclobber is set

<> file # uses file as both standard input and standard output

n<>file # uses file as both input and output for file descriptor n

n>file # directs file descriptor n to file

n<file # takes file descriptor n from file

n>>file # directs file description n to file; append to file if it already exists

n>& # duplicates standard output to file descriptor n

n<& # duplicates standard input from file descriptor n

n>&m # file descriptor n is made to be a copy of the output file descriptor

n<&m # file descriptor n is made to be a copy of the input file descriptor

&>file # directs standard output and standard error to file

<&- # closes the standard input

>&- # closes the standard output

n>&- # closes the ouput from file descriptor n

n<&- # closes the input from file descripor n

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# PROCESS HANDLING

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# To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y.

# This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal.

# Of course, to interrupt a job, type CTRL+C.

myCommand & # runs job in the background and prompts back the shell

jobs # lists all jobs (use with -l to see associated PID)

fg # brings a background job into the foreground

fg %+ # brings most recently invoked background job

fg %- # brings second most recently invoked background job

fg %N # brings job number N

fg %string # brings job whose command begins with string

fg %?string # brings job whose command contains string

kill -l # returns a list of all signals on the system, by name and number

kill PID # terminates process with specified PID

ps # prints a line of information about the current running login shell and any processes running under it

ps -a # selects all processes with a tty except session leaders

trap cmd sig1 sig2 # executes a command when a signal is received by the script

trap "" sig1 sig2 # ignores that signals

trap - sig1 sig2 # resets the action taken when the signal is received to the default

disown <PID|JID> # removes the process from the list of jobs

wait # waits until all background jobs have finished

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# TIPS & TRICKS

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# set an alias

cd; nano .bash_profile

> alias gentlenode='ssh admin@gentlenode.com -p 3404' # add your alias in .bash_profile

# to quickly go to a specific directory

cd; nano .bashrc

> shopt -s cdable_vars

> export websites="/Users/mac/Documents/websites"

source .bashrc

cd $websites

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# DEBUGGING SHELL PROGRAMS

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bash -n scriptname # don't run commands; check for syntax errors only

set -o noexec # alternative (set option in script)

bash -v scriptname # echo commands before running them

set -o verbose # alternative (set option in script)

bash -x scriptname # echo commands after command-line processing

set -o xtrace # alternative (set option in script)

trap 'echo $varname' EXIT # useful when you want to print out the values of variables at the point that your script exits

function errtrap {

es=$?

echo "ERROR line $1: Command exited with status $es."

}

trap 'errtrap $LINENO' ERR # is run whenever a command in the surrounding script or function exits with non-zero status

function dbgtrap {

echo "badvar is $badvar"

}

trap dbgtrap DEBUG # causes the trap code to be executed before every statement in a function or script

# ...section of code in which the problem occurs...

trap - DEBUG # turn off the DEBUG trap

function returntrap {

echo "A return occurred"

}

trap returntrap RETURN # is executed each time a shell function or a script executed with the . or source commands finishes executing