Question

What is a token? How does the shell decide where one token ends and other begins? 2) Assume the file list contains the names of several of the files listed in your home directory. What is the result of running the following? $ wc `cat list` 3) If a user enters the following with noclobber set off, what is the error message? Assume the file junk1 exists and the utility datxxx does not exist. What impact does issuing this command have? $datxx junk1 > junk1 4) How can you overwrite a file if noclobber is set in the bash shell? 5) Each blank line below indicates a token. How does the bash shell interpret each token in proper Linux syntax? Use U for utility, F for file and A for argument: A.$ < || > ; | B.$ | && ; ` | `|| C.$ | ; ` ` D.$ | $ > ; > Chapter 8 – Lab page 2 6) When a user issues the following distinct commands, what happens and why? Assume noclobber is not set and all files exist. A. $ CTRL-Z B. $ PATH=$PATH:~/mybin C. $ echo $? D. $ wc filexx > filexx E. $ cp –i fileCC fileDD 7) If noclobber is set on, and both files exist, what happens when the following command is issued: $mv fileAA fileBB

Answer 1

In shell scripting, a token is a sequence of characters treated as a single logical unit. The shell uses whitespace and special characters to determine token boundaries. The noclobber option prevents accidental overwriting of files during redirection but does not affect file operations like move.

Step-by-step explanation:

In computer programming, a token is a sequence of characters that are treated as a single logical entity by the compiler or interpreter. In shell scripting, the shell decides where one token ends and another begins based on whitespace or special characters such as operators or semicolons.

The command wc `cat list` would output the word count, line count, and byte count of the files listed in the file list, presuming these files are located in your home directory and are accessible.

With noclobber turned off, the command datxx junk1 > junk1 would result in an error message because datxx is not a valid command. This command would also truncate the file junk1 immediately as shell redirection (>) takes place before the command is executed.

When noclobber is set, to forcefully overwrite a file one can use the redirection operator >| instead of just >. For example, echo "data" >| filename would overwrite the file filename even if noclobber is set.

For the blank line representation, the shell interprets these tokens based on their function. For instance, $ is indicative of a variable, <, >, ||, ;, and | are shell operators, and the backticks (`) are command substitution indicators.

Regarding the distinct commands issued by a user:

1. CTRL-Z suspends the current foreground process, moving it to the background and pausing its execution.
2. By appending ~/mybin to the PATH variable, the shell is able to locate executables in that directory as well.
3. Issuing echo $? prints the exit status of the last run command, indicating success or failure.
4. wc filexx > filexx would replace the contents of filexx with its own word, line, and byte count, effectively overwriting it.
5. The cp -i command with two file arguments prompts the user before overwriting the destination file.

If noclobber is set and the command mv fileAA fileBB is issued, the move operation will proceed without issue, as noclobber only affects redirections, not file operations like move.