CNIT 340 Exam 2

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What is the character used for comments?

#

What is the first line of a bash script?

#!/bin/bash

What is the best way to enable debugging?

#!/bin/bash -xv

Arithmetic Substitution Syntax

$(( <expression> )) - Solutions will be integers (1.9 -> 1)

Command Substitution Syntax

$(<command>) and `<command>` Ex. DATE=$(date %s)

How do you access the number of elements in an array?

${#<name>[@]}

How do you access all values in an array?

${<name>[*]} - Returns All separated ${<name>[@]} - Returns elements as are for ex. Returns 4 elements: Walter Roger John George Douglas

How do you access a single value in an array?

${<name>[index]} Ex. ${NAME[0]}

What is the X11 Config Location?

/etc/X11

What is the PAM Config Location for X11?

/etc/pam.d/xdm

What is the return code for True?

0

Function Syntax

<function name> () { <code block> } OR function <function name> { <code block> }

Array Variable Format

<name>[index]=<value> Ex. NAME[0]=Walter

What must user defined variables start with?

A letter or underscore

User-defined variables best practice

ALL CAPS

Display Manager

Auth users & initialize environment

Array Variables

Can hold multiple elements at a time

Scalar Variables

Can only hold one element (value) at a time

What is ${<name>:?<message>} used for?

Catching errors if variable is unset.

What is another way to enable debugging?

DEBUG=true ./script.bash

Case syntax

case ITEM in pattern 1) <code block 1> ;; pattern 2) <code block 2> ;; esac

What command must you use to convert a windows text file to a unix text file?

dos2unix

Window Manager

move, resize, minimize, and maximize windows

What is the REGEX Result of: /[^0-9]/

negates - matches non-numbers The caret has a different meaning inside of brackets.

what does debugging option -n stand for?

no execution, useful for checking syntax errors

True or False: \ only disables the next character

True

How do you negate a character set?

With ! Ex. ls [!a-z]* Any filename that does not start with a lowercase letter

How do you access a variable?

With $, ex. $name

What symbols are used for quoting?

\ , ' , "

How do you save matches in registers?

\(regex\) saves matches in registers

What is the REGEX Result of: /^\(.\).*\1$/

^ Matches the beginning of the line \(.\) Matches the first character and stores it in register 1 .* Matches all the characters in between the first and last \1$ Matches the last character with contents of register 1

What is the REGEX Result of: /\.$/

matches "." if it is the last character in a line

What is the REGEX Result of: /^The/

matches "The" if it is the first chars in a line

What is the REGEX Result of: /The/

matches anything that starts with the

What is the REGEX Result of: /r./

matches r followed by any character

What is the REGEX Result of: /[A-Za-z]\{4,7\}/ Hint: \{min,max\}

matches strings of only upper and lower case alpha between 4 and 7 letters

What is the REGEX Result of: /X*/

matches zero or more of the character "X"

BASH Select loop syntax

select VAR in item1 item2 item3 do <Code Block> done OUTPUT A MENU: 1)item1 2)item2 3)item3

BASH Sequence syntax

seq <first> <step> <last> Ex. For VARIABLE in $(seq 1 2 20)

How do you debug certain portions of code?

set -n; <statement>; set +n

How do you tunnel X traffic through SSH?

ssh -X remote host

How do you turn off tunneling X traffic through SSH?

ssh -x remote host

How do you start an X server?

startx ( a wrapper of xinit)

How do you set a local variable in a function?

typeset VAR1=312

How do you delete a variable?

unset <name>

BASH until loop syntax

until <condition>; do <code block>; done

BASH while loop syntax

while <condition>; do <code block>; done

Types of BASH loops

while, until, for, select

X Client Authentication Types

Host Based (xhost) & magic cookie authentication

What is ${<name>:+<value>} used for?

If <name> is set, then the expression is replaced by <value> Ex. echo ${DEBUG:+"Program running in debug mode"} If DEBUG is set, then it will print to the screen

What is Filename substitution?

Expanding a string with wildcards (*, ?, [character set])

What is the difference between: FILES=$(ls) vs. FILES=($(ls))

FILES=$(ls) creates a scalar variable: $FILES = one two FILES=($(ls)) creates an array: $FILES[0] = one $FILES[1] = two

True or False: Compound Tests && (and), || (or), > and < work in Single Bracket tests

False

True or False: Array Variable Indices can be positive and negative.

False, only positive

[ -e file ]

File exists

[ -d file ]

File exists and is a directory

[ -f file ]

File exists and is a regular file

[ -s file ]

File exists and is of size greater than zero

[ file1 -nt file2 ]

File1 is newer than file2

[ file1 -ot file2 ]

File1 is older than file2

What are the types of Substitution?

Filename, Variable, Command, Arithmetic substitution

C Style Construct Example

For ((I=1; I<=10; I++))

X-Client

GUI applications

What does it mean if a variable starts with a number?

It is reserved (can use but not change)

What are the two types of variables?

Scalar & Array

What does ? do?

Matches any character one time

What does * do?

Matches any character zero or more times

What does [character set] do?

Matches the characters stated one time

What is the output of: unset NAME DIFFERENT=${NAME:-Walter} echo NAME $NAME, DIFFERENT $DIFFERENT

NAME , DIFFERENT Walter

What is the output of: unset NAME DIFFERENT=${NAME:=Walter} echo NAME $NAME, DIFFERENT $DIFFERENT

NAME Walter, DIFFERENT Walter

How do you make a variable readonly?

NAME=Walter readonly NAME

What is this equivalent to? NAME=(Walter Roger John "George Douglas")

NAME[0]=Walter NAME[1]=Roger NAME[2]=John NAME[3]="George Douglas"

Can read only variables be deleted?

NO

Can you return Strings in a function?

No

Is the following a valid statement? NAME=Walter Smith

No, assigned variables with spaces must be put in quotes: NAME="Walter Smith"

Are there blanks between 2 to 100 in this statement: NAME[101]=John

No, values are only assigned to the corresponding indices

X features

Not part of OS, Architecture Independent, Network Transparent, Policy Free

What expression matching does BASH support?

POSIX and PERL

X-server

Presents the output of an application to the display

What does debugging option -x stand for?

Shell tracing - display commands and args executed

What type of file is a shell script?

Text File

True or False: In Double Quoting $ and ` are still treated as meta-characters

True

True or False: Single Bracket keywords work on Double Bracket tests

True

BASH for loop syntax

for VARIABLE in <set> do <command block> done

full if elif else statement example

if <statement> then <code block 1> elif <statement> then <code block 2> else <code block 3> fi

if then syntax

if <statement>; then action; fi OR if <statement> then <code> fi


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