Tag: Bash Cheat Sheet

# 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 interupt a job, type CTRL+C.

myCommand &	runs the 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 the second most recently invoked background job
fg %N	brings job number N
fg %string	brings a job whose command begins with the string
fg %?string	brings a job whose command contains the string
kill -l	returns a list of all signals on the system, by name and number
kill PID	terminates the 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

# set an alias

cd; nano .bash_profile
> alias gentlenode='ssh [email protected] -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

bash -n scriptname	don’t run commands; check for syntax errors only
set -o noexec	alternative (set option in the script)
bash -v scriptname	echo commands before running them
set -o verbose	alternative (set option in the script)
bash -x scriptname	echo commands after command-line processing
set -o xtrace	alternative (set option in the 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 exists 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 occured"
}

trap returntrap RETURN

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

export	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 normal shell)
whereis bash	finds out where bash is on your system
clear	clears content on the window (hide displayed lines)

# File Commands.

ls	lists your files
ls -l	ists 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
ln -s <filename> <link>	creates a symbolic link to file
touch <filename>	creates or updates your file
cat > <filename>	places standard input into file
more <filename>	shows the first part of a file (move with space and type q to quit)
head <filename>	outputs the first 10 lines of a file
tail <filename>	outputs the last 10 lines of a file (useful with -f option)
emacs <filename>	lets you create and edit a file
mv <filename1> <filename2>	moves a file
cp <filename1> <filename2>	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 the file
chmod -options <filename>	lets you change the read, write, and execute permissions on your files
gzip <filename>	compresses files
gunzip <filename>	uncompresses files compressed by gzip
gzcat <filename>	lets you look at gzipped file without actually having to gunzip it
lpr <filename>	print the file
lpq	check out the printer queue
lprm <jobnumber>	remove something from the printer queue
genscript	converts plain text files into postscript for printing and gives you some options for formatting
dvips <filename>	print .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 a pattern in the directory

# Directory Commands.

mkdir <dirname>	makes a new directory
cd	changes to home
cd <dirname>	changes directory
pwd	tells you where you currently are

# SSH, System Info & Network Commands.

ssh user@host	connects to host as a user
ssh -p <port> user@host	connects to host on the specified port as user
ssh-copy-id user@host	adds your ssh key to host for a 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 the user
uname -a	shows kernel information
man <command>	shows the manual for the specified command
df	shows disk usage
du <filename>	shows the disk usage of the files and directories in the filename (du -s give only a total)
last <yourUsername>	lists your last logins
ps -u yourusername	lists your processes
kill <PID>	kills (ends) 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 the job to the foreground
ping <host>	pings host and outputs results
whois <domain>	gets whois information for the domain
dig <domain>	gets DNS information for the domain
dig -x <host>	reverses lookup host
wget <file>	downloads file

# Variables.

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] = val array[1] = val array[2] = val array=([2]=val [0]=val [1]=val)	several ways to define an array
${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 treated as arrays
declare -f	uses function names only
declare -F	displays function names without definitions
declare -i	the variables are treated 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 the 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 a variable is replaced by string. Only the first match is replaced
${variable//pattern/string}	the longest match to pattern in a 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 occurences of the given patterns
+(patternlist)	matches one or more occurences of the given patterns
?(patternlist)	matches zero or one occurence 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

# Functions.

# 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.

functname() {
shell commands
}

unset -f functname	deletes a function definition
declare -f	displays all defined functions in your login session

# Flow Control.

statement1 && statement2	and operator
statement1 || statement2	or operator
-a	and the operator inside a test conditional expression
-o	or operator inside a test conditional expression
str1=str2	str1 matches str2
str1!=str2	str1 does not match str2
str1<str2	str1 is less than str2
str1>str2	str1 is greater than str2
-n str1	str1 is not null (has length greater than 0)
-z str1	str1 is null (has length 0)
-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
-r file	file exists and is not empty
-w file	you have to write permission
-x file	you have executed permission on file, or directory search permission if it is a directory
-N file	the 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
-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 := 1 to 10 do
begin
    statements
end

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

cmd1|cmd2	pipe; takes the standard output of cmd1 as standard input to cmd2
> file	directs standard output to file
< file	takes standard input from the 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
<<label	here-document
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 output from file descriptor n
n<&-	closes the input from file descriptor n

CTRL+A	move to the beginning of the line
CTRL+B	moves backward one character
CTRL+C	halts the current command
CTRL+D	deletes one character backward or logs out of the current session, similar to exit
CTRL+E	moves to the 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 the end of line
CTRL+L	clears the screen and redisplay the line
CTRL+M	same as RETURN
CTRL+N	next line in the command history
CTRL+O	same as RETURN then displays the next line in a history file
CTRL+P	previous line in the 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 the line
CTRL+V	makes the next character typed verbatim
CTRL+W	kills the word behind the cursor
CTRL+X	lists the possible filename completion of the current word
CTRL+Y	retrieves (yank) the last item killed
CTRL+Z	stops the current command, resume with fg in the foreground or bg in the background
DELETE	deletes one character backward
!!	repeats the last command
exit	logs out of current session