70 Classic Shell Script interview questions

1) How do I pass parameters to a script?

./script argument

Example : Show file name script

./show.sh File1.txtcat Show.sh#!/bin/bashcat $

2) How do I use parameters in a script?

First parameter: $ $, second argument: $ A

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

./copy.sh File1.txt/tmp/cat COPY.SH#!/BIN/BASHCP $ $

3) How to calculate the parameters passed in?

$#

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

$

5) How do I check if the previous command was successful?

$?

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

Tail-1

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

Head-1

8) How do I get a third element for each line of a file?

awk ' {print $} '

9) How to get the second element if the first element in each row of the file is FIND

awk ' {if ($ = = ' FIND ') print $ '

10) How to debug a bash script

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

Example:

#!/bin/bash–xv

11) For example, how to write a function?

Function Example {echo "Hello world!"}

12) How to connect two strings?

v1= "Hello" v2= "World" v3= $V 1+ $V 2echo $V 3

Output

Hello+world

13) How do I add two integers?

v1=1v2=2v3= $V 1+ $V 2echo $V 3

Output

3

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

If [-f/var/log/messages]thenecho "File exists" fi

15) write out all the loop syntax in the shell script? For loop:

For I in $ (LS); Doecho Item: $idone

While loop:

#!/bin/bashcounter=0while [$COUNTER-lt 10]; Doecho The counter is $COUNTERlet Counter=counter+1done

Until cycle:

#!/bin/bashcounter=20until [$COUNTER-lt 10]; Doecho COUNTER $COUNTERlet Counter-=1done

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

This line describes the shell to use. #!/bin/bash indicates that the script uses/bin/bash. For Python scripts, this is #!/usr/bin/python. (LCTT: This line is called the release companion line.) ）

17) How do I get to the 10th line of a text file?

Head-10 FILE|TAIL-1

What is the first symbol of a bash script file?

#

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

0

20) What is the use of the command "Export"?

Make the variable available in the child shell.

21) How do I run scripts in the background?

Add "&" after the script.

What do you do with "chmod script"?

Enables the script owner to have executable permissions.

What does ">" Do?

Redirects the output stream to a file or to another stream.

What is the difference between & and &&

• &– want the script to be used when it runs in the background
• &&– the current script completes successfully before executing the command/script, use it

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

You need to run multiple commands when the condition is met.

26) Command: Name=john && Echo ' My name is $name ' what is the output

My name is $name

What symbols in the Bash shell script are used for comments?

#

28) Command: What is the output of 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.
• – The values of all variables are computed and replaced by values.

30) How do I redirect standard output and standard error streams to the Log.txt file in a script file?

Add the Exec >log.txt 2>&1″ command to 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 I get home_dir with the echo command only?

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

Or

echo ${variable##*:}

33) How do I Get "User" from the string above?

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

Or

echo ${variable%%:*}

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

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

35) Write the 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 gdo{echo $c; grep: $g:/etc/group|cut-d:-f1;}| Xargs-n 2done

36) How do I change the standard domain 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 you have not previously assigned a value to variable
• ${variable: The last 10 characters of the -10}– output variable

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

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 do I calculate the number of words in a string without the WC command?

Set ${string}echo $#

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

Export variable

45) How to list the second letter is a or b file?

Ls-d? [ab]*

46) How do I add an 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 remove all the spaces in a string?

echo $string |tr-d ""

48) Rewrite this command to convert the output variable to a complex number: item= "Car"; echo "I like $item"?

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

49) write out the output number 0 to 100 in multiples of 3 (0 3 6 9 ...) 's orders?

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 parameters passed to the script?

Echo $*

Or

echo [email protected]

What is the difference between [$a = = $b] and [$a-eq $b]

• [$a = = $b]– for string comparisons
• [$a-eq $b]– for digital comparisons

52) = and = = What is the difference

• =– used to copy a variable
• ==– for string comparisons

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

[$a-GT 12]

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

[$b-le 12]

55) How do I check if a string begins with the letter "ABC"?

[[$string = = abc*]]

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

• [[$string = = abc*]]– Check if the string starts with the letter ABC
• [[$string = = "ABC"]]– check if the string is exactly equal to ABC

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

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

($!) in bash What does that mean?

The PID of the recently executed command in the background.

59) $? What does that mean?

The end state of the last command in the foreground.

60) How to output the current shell PID?

Echo $$

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

Echo $#

(LCTT: And the 3rd question repeats.) ）

62) What is the difference between $* and [email protected]

• $*– output all parameters passed to the script as a string
• [Email protected]– to list all parameters passed to the script in $IFS delimiter

63) How do I define an array in bash?

array= ("Hi" "My" "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 input value?

A) by parameter

./script param1 param2

b) through the Read command

Read-p "Destination backup Server:" Desthost

70) How do I use "expect" in the script?

/usr/bin/expect << eodspawn Rsync-ar ${line} ${desthost}:${destpath}expect "*?assword:*" Send "${password}/r" Expect Eofeod

70 Classic Shell Script interview questions