You want to write a shell script that:

Creates a directory called backup, if it doesn't already exist, and
Copies all .txt files from the current directory into the backup directory.

Which of the following code snippets (if any) will achieve this?

Question

You want to write a shell script that:

Creates a directory called backup, if it doesn't already exist, and
Copies all .txt files from the current directory into the backup directory.

Which of the following code snippets (if any) will achieve this?

BlackTom AI · Accepted Answer

Question: You want to write a shell script that:

Creates a directory called backup, if it doesn't already exist, and
Copies all .txt files from the current directory into the backup directory.

Which of the following code snippets (if any) will achieve this?

Options:
1) mkdir -p backup
cp *.txt backup/

2) None of the other answers is correct

3) mkdir backup
cp *.txt backup/

4) if [ ! -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/

5) if [ -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/

Analysis of each option:
Option 1: mkdir -p backup
cp *.txt backup/

- The -p flag in mkdir ensures that the directory is created if it does not exist and does nothing if it already exists. This directly satisfies the requirement to create the directory only when needed. The subsequent cp command copies all .txt files from the current directory into the backup directory, leveraging a simple wildcard (*.txt). This combination is concise and robust, handling both creation and copying in a straightforward way.

Option 2: None of the other answers is correct

- This statement would be accurate only if all other options failed to meet the requirements. Since option 1 (and option 4, as discussed later) actually accomplishes the task, this claim is not correct.

Option 3: mkdir backup
cp *.txt backup/

- This sequence creates a directory named backup without the -p flag. If the directory already exists, mkdir will fail with an error, and the script will stop or continue depending on the shell settings. Because the requirement specifies creating the directory if it doesn’t exist, this option is not reliable in the general case where backup may already be present.
- Additionally, the copy command itself is fine, but the risk of mkdir failing on an existing directory makes this option inadequate.

Option 4: if [ ! -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/

- This option first checks whether the backup directory exists; if it does not, it creates it. After that, it copies all .txt files into backup. This approach satisfies the requirement and is robust in environments where -p is unavailable or you want to explicitly guard creation. The copy step is executed unconditionally after the check, so it will work whether or not the directory needed creation.

Option 5: if [ -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/

- This logic is flawed: it attempts to create the directory only if it already exists (the condition checks for the directory’s existence and then runs mkdir). If the directory exists, the mkdir will be attempted (which is unnecessary and could fail with an error). If the directory does not exist, the mkdir is skipped, and the copy still runs, leading to a failure because the destination directory isn’t present. Overall, this does not reliably create the directory when needed and is not correct for the stated goal.

Putting it together, the most reliable and concise snippets that achieve the stated goal are the ones that ensure the backup directory exists before copying. Option 1 does this in a single line with mkdir -p and then copies, making it a clean solution. Option 4 also achieves the same objective with an explicit existence check followed by creation when necessary. Both approaches meet the requirements, while options 3 and 5 are problematic, and option 2 would only be correct if none of the other options worked.

FA25_ISOM_661_4102 Shell - MC Quiz

You want to write a shell script that: Creates a directory called backup, if it doesn't already exist, and Copies all .txt files from the current directory into the backup directory. Which of the following code snippets (if any) will achieve this?

查看解析

登录即可查看完整答案

类似问题

Question at position 9 Given the following shell variable assignments, a=2; b=5; c=10 Which of the following conditions is true? [ $a –eq 3 –o $b –ge 5 ][ $b –gt 5 ][ $c = (3 + 7) ][ a –eq 2 ]

Shell command (1 mark)How many lines will be output by the following shell command? cat data.csv | awk -F’,’ ’rand()<9/10 {print $9}’[Fill in the blank]

To execute a Unix shell script TEST.SH, you may use

A UNIX shell script program file is

You want to write a shell script that: Creates a directory called backup, if it doesn't already exist, and Copies all .txt files from the current directory into the backup directory. Which of the following code snippets (if any) will achieve this?

The purpose of code "#! /bin/sh" at the beginning of a Unix script is

In a Unix shell script, what command is used to accept user's input?

更多留学生实用工具

考试浏览器助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单