Shell Script Classic face test 70, with answers

This article prepares 70 shell script interview questions and answers, and shell scripts are the skills that must be mastered in Linux work.

1 How can I pass parameters to a script?

./script argument

Example: Display file name script

./show.sh File1.txt

Cat show.sh
#!/bin/bash
Cat $

2 How do I use parameters in a script?

First argument: $, second argument: $

Example: The script will copy the file (arg1) to the destination address (ARG2)

./copy.sh file1.txt/tmp/

Cat copy.sh
#!/bin/bash
CP $ $

3 How to calculate the parameters passed in?

$#

4 How do I get the script name in the script?

$

5 How to check if the previous command is running successfully?

$?

6 How do I get the last line of the file?

Tail-1

7 How do I get the first line of the file?

Head-1

8 How do I get a third element of each row of a file?

awk ' {print $} '

9 if the first element of each line in the file is find, how to get the second element

awk ' {if ($ = ' find ') print $} '

10 How to debug a bash script

After adding the-XV parameter to the #!/bin/bash

Example:

#!/bin/bash XV?

11 example how to write a function?

function Example {
echo "Hello world!"
}

12 How to connect two strings?

v1= "Hello"
V2= "World"
V3=${V1}${V2}
Echo $V 3

Output

HelloWorld

13 How do I add two integers?

V1=1
v2=2
Let v3= $V 1+ $V 2
Echo $V 3

Output

3

According to @kashu opinion, the better answer to the question is:

Add two integers, there are several ways to do this:

A=5
B=6

echo $ (($A + $B)) # method 2
echo $[$A + $B] # Method 3
Expr $A + $B # Method 4
echo $A + $B | BC # Method 5
awk ' begin{print ' $A ' + ' ' $B '} ' # Method 6

14 How do I check if a file exists in the file system?

if [-f/var/log/messages]
Then
echo "File exists"
Fi

15 Write all the looping syntax in the shell script?
For loop:

For I in $ (LS); Todo
Echo Item: $i
Done

While loop:

#!/bin/bash
Counter=0
While [$COUNTER-lt 10]; Todo
echo the counter is $COUNTER
Let Counter=counter+1
Done

Until cycle:

#!/bin/bash
Counter=20
Until [$COUNTER-lt 10]; Todo
Echo COUNTER $COUNTER
Let Counter-=1
Done

16 What does the #!/bin/sh or #!/bin/bash at the beginning of each script mean?

This line shows the shell to use. #!/bin/bash indicates that the script uses/bin/bash. For Python scripts, it's #!/usr/bin/python. (LCTT: This line is called the companion line.) ）
17 How do I get the 10th line of the text file?

Head-10 FILE|TAIL-1

The first symbol of the bash script file

#

19) Command: [-Z ""] && echo 0 | | What is the output of echo 1?

0

20 What is the use of the order "export"?

Make the variable available in the child shell.
21 How to run the script in the background?

Add "&" after the script.

According to @kashu opinion, the better answer is:

Nohup Command &

Most of the time we could be using Linux remotely, and I've encountered Command & that runs in the background because the network is disconnected ...

What does "chmod" do?

Make the script owner have executable permissions.
">" What to do?

Redirects the output to a file or to another stream.
& && What's the Difference

&-Want the script to run in the background and use it
&&-use it when the current script completes successfully before executing the command/script later

25 when do you want to use "if" before [condition]?

When conditions are met, multiple commands need to be run.
26 Command: What is the output of Name=john && echo ' My name is $name '

My name is $name

In bash shell script which symbol is used for annotation?

#

28) Command: What is the output of the Echo ${new:-variable}

Variable

29) What is the difference between ' and ' quotes?

'-use it when we don't want to convert the variable to a value.
"-Calculates the value of all variables and replaces them with values.

30 How to redirect standard output and standard error stream to Log.txt file in script file?

Add the "Exec >log.txt 2>&1" command in the script file.
31 How do I get only part of a string variable with the echo command?

Echo ${variable:x:y}
X-Start position
Y-Length

Example:

Variable= "My name is Petras, and I am developer."
Echo ${variable:11:6} # will show Petras

32 if the given string variable= "User:123:321:/home/dir", how can you get home_dir only with the echo command?

echo ${variable#*:*:*:}

Or

echo ${variable##*:}

33 How do I get "User" from the string above?

echo ${variable%:*:*:*}

Or

echo ${variable%%:*}

34 How do I use awk to list users with a UID of less than 100?

Awk-f: ' $3<100 '/etc/passwd

35 Write program for the user to calculate the number of primary groups and display the number and group name

Cat/etc/passwd|cut-d:-f4|sort|uniq-c|while Read C G
Todo
{echo $c; grep: $g:/etc/group|cut-d:-f1;}| Xargs-n 2
Done

36 How do I change the standard field delimiter in the bash shell to ":"?

Ifs= ":"

37 How do I get the variable length?

${#variable}

38 How do I print the last 5 characters of a variable?

echo ${variable:-5}

${VARIABLE:-10} and ${variable:-10} What's the difference?

${VARIABLE:-10}-Output 10 If the variable has not been assigned before, and output if there is a value assigned
${variable:-10}-Output variable last 10 characters

40 How do I replace part of a string with the echo command only?

Echo ${variable//pattern/replacement}

41 which command replaces the command with uppercase?

TR ' [: Lower:] ' [: Upper:] '

42 How to calculate the number of local users?

Wc-l/etc/passwd|cut-d ""-f1 or Cat/etc/passwd|wc-l
43 How to calculate the number of words in a string without WC command?

Set ${string}
Echo $#

"Export $variable" or "Export variable" which is correct?

Export variable

45 How do you list a file with the second letter A or B?

Ls-d? [ab]*

46 How do I add integer A to B and assign a value to C?

c=$ ((a+b))

Or

C= ' expr $a + $b '

Or

C= ' echo ' $a + $b ' |BC '

47 How do I get rid of all the spaces in the string?

echo $string |tr-d ""

48 rewrite This command to convert the output variable to plural: item= "car"; echo "I like $item"?

item= "Car"; echo "I like ${item}s"

49 write out a multiple of 3 in the output number 0 through 100 (0 3 6 9 ...) 's order?

For i in {0..100..3}; do echo $i; Done

Or

for ((i=0; i<=100; i=i+3)); Do echo "Welcome $i times"; Done

50 How do I print all the parameters passed to the script?

Echo $*

Or

Echo $@

What's the difference [$a = = $b] and [$a-eq $b]

[$a = = $b]-for string comparisons
[$a-eq $b]-for numeric comparisons

52 = and = = What is the difference between

=-Used to assign values to variables
= =-for string comparisons

53 Write the test $a is greater than 12 command?

[$a-GT 12]

54 Write the test $b is less than or equal to 12 command?

[$b-le 12]

55 How do I check if the string starts with the letter "ABC"?

[[$string = = abc*]]

[[$string = = abc*]] and [[$string = = "abc*"]] what's the difference

[[$string = = abc*]]-checks whether the string starts with the letter ABC
[[$string = = "abc"]]-check that the string is exactly equal to ABC

57 How do I list the user names that start with AB or XY?

Egrep "^ab|^xy"/etc/passwd|cut-d:-f1

$! in Bash What does that mean?

The PID for the most recent command execution in the background.
59) $? What does that mean?

The end state of the most recent command at the foreground.
60 How to output the current shell PID?

Echo $$

61 How do I get the number of parameters passed to the script?

Echo $#

(LCTT: Repeat with question 3rd.) ）
62 What's the difference between $* and $@?

$*-Output all parameters passed to the script as a string
$@-Lists all parameters passed to the script in $IFS as delimiters

63 How do I define an array in bash?

array= ("Hi" "I" "Name" "is")

64 How do I print the first element of an array?

Echo ${array[0]}

65 How do I print all the elements of an array?

Echo ${array[@]}

66 How do I output all the array indexes?

Echo ${!array[@]}

67 How do I move an element with an index of 2 in the divisor group?

Unset Array[2]

68 How do I add an element with ID 333 in an array?

array[333]= "New_element"

How does the shell script get the value entered?

A) through the parameters

./script param1 param2

b) through the Read order

Read-p "Destination backup Server:" Desthost

70 How do I use "expect" in a script?

/usr/bin/expect << EOD
Spawn Rsync-ar ${line} ${desthost}:${destpath}
Expect "*?assword:*"
Send "${password}\r"
Expect EOF
EOD