Bash Shell

Question 1

Variable and function syntax

Answer 1

FOO=bar
VAR2=/home/user/docs
function yo()
{
  echo "yo"
}

Question 2

List of all exported shell variables

Command used to allow child sessions to use env vars

Answer 2

1. export
2. export FOO=bar
3. export PATH=$PATH:/home/user/programs

Question 3

Show environment vars

Answer 3

env

Question 4

List shell settings or shell vars and funcs for the session

Answer 4

set
set -x/set +x- turn on/off she debugging
set -f -enable file globbing
set +f -disable file globbing

Question 5

Remove var or function

Answer 5

unset -f yo

unset FOO

Question 6

Display shell options

Modify shell options

Answer 6

shopt
shopt -s histreedit- set
shopt -u histreedit -unset

Question 7

Locate an app file listed in $PATH

Answer 7

which bash

Question 8

Determine if something is a function, file, alias, built-in or keyword

Answer 8

type cd=> function

type type=> built-in

Question 9

Interactive login shell

Answer 9

/etc/profile=>/etc/profile.d/*

info from /etc/profile.d/ returns back to /etc/profile=>~/.bash_profile or ~/.profile =>~/.bashrc=>/etc/bashrc

Question 10

Interactive non-login shell

Answer 10

~/.bashrc=>/etc/bashrc

Question 11

First file read on login session. Sets env vars such as PATH, umask, bash history controls

Answer 11

/etc/profile

Question 12

Configs of system-wide functions and aliases

Answer 12

/etc/bashrc

Question 13

Templates of files that are added when an account is created

Answer 13

/etc/skel

Question 14

Legacy ~/.bash_profile file

Answer 14

~/.bash_login

Question 15

Set alias

Answer 15

vim ~/.bashrc
alias ll=”ls -la”
source ~/.bashrc or . ~/.bashrc

Question 16

Run command from history

Answer 16

!56

run 56 line from history

Question 17

Location of history

Answer 17

~/.bash_history

Question 18

Env var keeping size of line in .bash_history

Answer 18

HISTFILESIZE

Question 19

Man pages

Answer 19

1. exec programs and shell commands
2. system calls- function provided by kernel
3. library calls
4. special files typically found in /dev
5. files formats and conventions
6. games
7. miscellaneous
8. for sysadmins
9. for non-standard kernel routines

Question 20

Get pid of current bash process

Answer 20

echo $$

Question 21

Expand escaping chars to be printed in echo example

Answer 21

echo -e “This is an example of \n escaping chars \t\t !!”

Question 22

Exit codes

Answer 22

0= no issue
!=0 -issue
1. execute any command
2. echo $? to get exit value

Question 23

Conditional statements

Answer 23

!/bin/bash

var=$1
if [ $var == 1 ]
then
    echo  "$var eq one"
fi
if [ $var -ne 2 ] && [ $var -ne 1 ]
then 
    echo "$var equals 3"
fi

case $var in
1)
echo “in this case the positional parameter eq 1”
;;
2)
echo “in this case the positional parameter eq 2”
;;
3)
echo “in this case the positional parameter eq 3”
;;
esac

Question 24

Loops

Answer 24

!/bin/bash

for i in {1..5}
do
echo $i
done

echo 'for loop is complete'
counter=6
while [ $counter -le 9 ]
do
    echo $counter
    counter=$[ $counter+1 ]
done

echo ‘while loop is complete’

number=10
until [ $number -eq 15 ]
do
    echo $number
    ((number++))
done

Question 25

Positional parameters to be set into the script

Answer 25

!/bin/bash

set – first1 second1 third1

echo “the first arg is $1”
echo “the second arg is $2”
echo “the third arg is $3”

echo “the name of the script is $0”