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

First, let's restate the task and the options to ensure understanding of what's being evaluated.
The goal is to create a directory named backup if it doesn't already exist, and then copy all .txt files from the current directory into that backup directory.
Option A: None of the other answers is correct
Option B: mkdir -p backup
cp *.txt backup/
Option C: if [ ! -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/
Option D: mkdir backup
cp *.txt backup/
Option E: if [ -d "backup" ]; then
  mkdir backup
fi
cp *.txt backup/

Option B analysis:
- The command mkdir -p backup uses the -p flag, which creates the directory only if it doesn't exist and does not error if it already exists. This satisfies the requirement to create the directory if needed.
- The subsequent cp *.txt backup/ copies all .txt files into the backup directory. This sequence is simple and robust. Therefore, B is correct.

Option C analysis:
- The if [ ! -d "backup" ]; then mkdir backup; fi block checks for the absence of the directory and creates it if missing, which also satisfies the requirement.
- The following cp *.txt backup/ copies the .txt files into the directory. This works as well, so C is also correct.

Option D analysis:
- This snippet uses mkdir backup without -p. If the backup directory does not exist, it creates it—that part is fine.
- However, if backup already exists, mkdir will return an error and may cause the script to fail or continue depending on settings. Since the goal specifies creating only if it doesn't exist, this snippet is not robust and can fail in the common case where backup exists. Thus, D is not reliably correct.

Option E analysis:
- The condition if [ -d "backup" ]; then checks whether the directory exists, and only then attempts to run mkdir backup inside the block. If the directory exists, this block runs but does nothing effective; if it does not exist, the mkdir backup is skipped entirely. Therefore this snippet fails to guarantee the directory exists and is not a correct solution. E is incorrect.

Option A analysis:
- Claiming that none of the other answers is correct is inaccurate, since at least B and C provide valid, functional solutions.

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?多项选择题

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