If Then Comparisons

Question 1

-eq

Answer 1

equal to (for numbers)

Question 2

[[ STRING == STRING ]]

Answer 2

equal to (for strings)

Question 3

-ne

Answer 3

not equal to (for numbers)

Question 4

[[ STRING != STRING ]]

Answer 4

not equal to (for strings)

Question 5

-lt

Answer 5

less than (for numbers)

Question 6

-le

Answer 6

less than or equal to (for numbers)

Question 7

-gt

Answer 7

greater than (for numbers)

Question 8

-ge

Answer 8

greater then or equal to (for numbers)

Question 9

Write an
if statement

include the additional syntax options.

Answer 9

if commands; then
    commands

[elif commands; then 
    commands...]

[else 
    commands]
fi

Question 10

Special variables:
$?

Answer 10

Exit status of
last task:
0-255

Question 11

Special variables:
$!

Answer 11

PID of last background task

Question 12

Special variables:
$$

Answer 12

PID of shell

Question 13

Special variables:
$0

Answer 13

Filename of the shell script

Question 14

Special variables:
$_

Answer 14

Last argument of the previous command

Question 15

Special variables:
${PIPESTATUS[n]}

Answer 15

return value of
piped commands
(array)

Question 16

Exit status 0

Answer 16

0 indicates success

Question 17

Exit status 1

Answer 17

Any exit status other than 0 means failure

Question 18

[[ -z STRING ]]

Answer 18

empty string, true

Question 19

[[ -n STRING ]]

Answer 19

not empty string, true

Question 20

[[ STRING =~ REGEX ]]

Answer 20

Compares String against a Regexp (for strings)

Example:
LINE=”Spaces Present”
NOLINE=”SpacesNotPresent”
if [[ “${NOLINE}” =~ [[:space:]] ]]; then
echo “true for ${NOLINE}”
#echo “Line Number: ${LINENO}”
else
echo “false for ${NOLINE}”
fi

This will print for $LINE but false for $NOLINE

Question 21

(( NUM < NUM2 ))

Answer 21

Evaluating numerical conditions, specifically NUM2 is greater than NUM, then TRUE

Question 22

What is clobbering in bash shell?

Answer 22

The process of overwriting existing data [files].

Question 23

What is noclobber in bash shell?

Answer 23

A setting that will make the shell complain if a redirect is trying to overwrite an existing file.

Question 24

How do you enable noclobber?

Answer 24

$ set -o noclobber

to check the setting:
$ set -o | grep clobber

Question 25

How do you disable noclobber?

Answer 25

$ set +o noclobber

Question 26

[[ -o noclobber ]]

Answer 26

If OPTIONNAME is enabled. Example is noclobber.

Question 27

[[ ! EXPR ]]

Answer 27

Not

Question 28

[[ X && Y ]]

Answer 28

And

Question 29

[[ X || Y ]]

Answer 29

Or

Question 30

Bash Options:
$ set -o noclobber

Answer 30

Avoid overwriting files (echo “hi” > foo)

Question 31

Bash Options:
$ set -o errexit

Answer 31

Used to exit upon error, avoiding cascading errors

Question 32

Bash Options:
$ set -o pipefail

Answer 32

Unveils hidden failures

Question 33

Bash Options:
$ set -o nounset

Answer 33

Exposes unset variables