Linux Admin

Suppose that you have an application whose behavior depends on the environment variable BAR. Which of the following command lines may be used in a bash shell to configure the application?

• export $BAR=baz; echo $BAR

• set BAR=baz

• BAR=baz ; export BAR

• echo BAR=baz

• declare -x BAR=baz

Which of the following commands can be used to assure that a file 'myfile' exists?

• cp myfile /dev/null

• touch myfile

• create myfile

• mkfile myfile

Which of the following command lines can be used to convert a file containing DOS-style CR-LF line endings into Unix-style LF line endings? Assume for this question that the DOS-style file is called 'dosfile', and we want the modified contents in 'unixfile'

• sed 's/\r//' dosfile > unixfile

• tr -d '\r' < dosfile > unixfile

• dos2unix dosfile unixfile

• strip '\r' < dosfile > unixfile

Suppose for this question that you have a file called 'wordlist' that contains a number of words, one per line. You would like to produce an ad-hoc report that contains a numbered list of the first five words, according to alphabetical order. Which of the following command lines can be used to produce this report to the console?

• sort wordlist | nl | head -5

• split -1 wordlist ; cat xa? | head -5

• nl wordlist | sort | sed '/^ [^12345]/d'

• nl wordlist | sort | head -5

The command 'ps -A' displays an ordered list of all running processes, with the right-justifed process ID in the first space-separated field. Suppose you would like to display to screen a list of the five most recently launched processes (those with the highest process IDs). Which of the following

commands will display the desired items?

• ps -A | tail -5 | cut -f 1 -d " "

• ps -A | tail -5 | sed 's/[ ]*[0-9]*//'

• ps -A | head -5 | nl

• ps -A | tac | head -5 | cut -b 0-5

Suppose that a file 'names' contains a list of names in the form, "firstname lastname", one per line. These names are unsorted, and you would like them sorted by lastname; however, the format of names on each line should remain the same. Which ONE of the following commands will NOT output an appropriately sorted list of names to the console?

• cut -f 2 -d " " names | paste names - | sort -k 3 | cut -f 1

• sort -k 2 names

• sed 's/\(\w*\) \(\w*\)/\2\1\2/' names | sort | cut -f2-3 -d" "

• cut -f 2 -d " " names | sort

• cut -f 2 -d " " names | paste - names | sort | cut -f 2