70 Classic Shell Script interview questions

Source: Internet
Author: User
Tags echo command

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


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


13) How do I add two integers?
v1=1v2=2v3= $V 1+ $V 2echo $V 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?
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}
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


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#*:*:*:}


echo ${variable##*:}
33) How do I Get "User" from the string above?
echo ${variable%:*:*:*}


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?
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))


C= ' expr $a + $b '


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


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 $*


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

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