week 7 Flashcards
Brace Expansions
Bash can fill in a pattern contained in braces
I.E echo {1 .. 10 .. 2}
command substitution
allows you to store the output of a command in a variable
ie list = $(ls)
arithmetic expansion
Evaluates a mathematical expression inside
ie $(( arithmetic ))
pattern matching: *
matches any sequence of characters
pattern matching: ?
matches any single character
pattern matching: []
matches any enclosed characters
Declaring function in Bash
function() {
body
}
How do you pass a argument into a bash function?
you must use positional parameters ie $1
Local variables
use the keyword ‘local’ behind what you want to be local scoped only
i.e. local users=$@
How do you return a value in a bash function?
Assign the value to a var and echo the var
Case
alternative to if/elif/else statements, allows you to patter match possible options and return something different depending
;; = end of condition
| = alternate condition
esac = end
i.e Case expression in:
A)
Echo A
;;
B)
echo B
;;
*)
echo everything
;;
esac
OPTARG
OPTARG contains the arguments used for each flag and is generally used in conjunction with while and case
while getopts “:a:b:” opt; do
case “${opt}” in
a) example=${OPTARG}
esac
done
shift
Shifts positional parameters n characters to the left, shift can stack with each other
what is YAML?
“YAML ain’t markup language”, a human readable, data serialization language
What command do you use to quit a process?
kill
what signal is sent by default when using the “kill” command?
SIGTERM
How do you send a different signal/SIGKILL with kill?
kill -9 or kill -SIGKILL
How to show %mem with ps?
ps aux
option: add –sort=-%mem
What is the signal code for sigint?
2
what is the signal code for SIGKILL
9
what is the signal code for SIGTERM
15
How to find all lines that begin with a certain word? (regex)
grep “^GNU”
how to find lines that end with a certain word? (regex)
grep “word$”
What’s the difference between “.” and “?” in regex?
”?” matches for zero or more occurences while “.” matches any character
How to add user to a group>
sudo usermod –aG groupname username
How do you set password expiry?
sudo chage -M days username
how to change ownership of a file?
sudo chown username:group filename
-R for recursive
Where would you find a list of groups?
/etc/group
command for creating a new group
groupadd
Where is the config file for nvim located?
/home/user/.config/nvim/init.lua
what does the shebang do?
tells the shell what interpreter to use
how to make variable accessible in subshell?
export $var
what would you use declare for?
- creating an associative array (-A)
- provide attributes to variables (-r for readme, NUM for int variable)
how to check if a file is older than another one using conditionals in scripting?
-ot
How to get all array items?
array[@]
how to get number of items in an array?
array[@]
what’s the difference between pkill and kill?
pkill allows you to kill a process via the process name while kill uses PID
