Using vi， you want to save changes to the file myfile with ：w!， but vi complains it cannot write to the file. Therefore， you want to check the write permissions on the file. To do this without leaving vi， you type：（）

单项选择题YouwishtokillaprocesswithaPIDof123.Selectthecommandwhichexiting.（）

A. kill-1 123
B. kill-9 123
C. kill-15 123
D. kill-17 123

单项选择题WhichofthefollowingcommandswillchangeallCR-LFpairsinanimportedtextfile，userlist.txt，toLinuxstandardLFcharactersandstoreitasnewlist.txt？（）

A. tr ’\r\n’ " < userlist.txt > newlist.txt
B. tr -c ’\n\r’ " < newlist.txt > userlist.txt
C. tr -d \r¯ < userlist.txt > newlist.txt
D. tr \r¯\n¯ userlist.txt newlist.txt
E. tr -s ®^M’¡®^J’ userlist.txt newlist.tx

单项选择题Youhaveread writepermissiononanordinaryfilefoo.YouhavejustrunInfoobar.Whatwouldhappenifyouranrmfoo？（）

A. foo and bar would both be removed.
B. foo would be removed while bar would remain accessible.
C. foo would be removed， bar would still exist but would be unusable.
D. Both foo and bar would remain accessible.
E. You would be asked whether bar should be removed.

单项选择题WhatisthedifferencebetweenthE.removeandthE.purgeactionwiththedpkgcommand？（）

A. -remove removes the program， -purge also removes the config files
B. -remove only removes the program， -purge only removes the config files
C. -remove removes a package， -purge also removes all packages dependent on it
D. -remove removes only the package file itself， -purge removes all files related to the package

单项选择题Thecommandecho$!willproducewhatoutput？（）

A. the process id of last background command
B. the exit status of the last command
C. the exit status of the last background command
D. the process id of the current shell
E. the name of the command being executed