Which of the following will always output "maple"?

  1. tree=maple; export tree; sh -c "echo $tree"

  2. tree=maple; export $tree; sh -c "echo $tree"

  3. $tree=maple; echo $tree

  4. export tree = maple; echo $tree


Correct Option: A

AI Explanation

To answer this question, we need to understand how variable assignment and echoing work in shell scripting.

Option A) tree=maple; export tree; sh -c "echo $tree" - This option is correct. Here, the variable "tree" is assigned the value "maple", then it is exported using the "export" command. The "sh -c" command is used to run the following command in a subshell. The "echo $tree" command is used to print the value of the variable "tree", which is "maple".

Option B) tree=maple; export $tree; sh -c "echo $tree" - This option is incorrect. In this case, the variable "tree" is assigned the value "maple", but when exporting the variable using "export $tree", the shell will interpret it as exporting the value of the variable "maple" (which is empty). Therefore, the echoed value will be empty.

Option C) $tree=maple; echo $tree - This option is incorrect. When assigning the value "maple" to the variable "$tree", the shell will interpret it as trying to assign the value of a variable named "maple" to the variable "$tree", which is not what we want. Therefore, this option will result in an error.

Option D) export tree = maple; echo $tree - This option is incorrect. When exporting a variable, we should not include spaces around the "=" sign. So, the correct syntax should be "export tree=maple". Additionally, the echo command should be used after the export command to print the value of the variable. Therefore, this option will result in an error.

The correct answer is Option A. This option correctly assigns the value "maple" to the variable "tree", exports it, and then prints the value of the variable using the echo command.

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