Q1 60-80

Question 1

When will ‘wc < chap0[1-5]’ work?

Answer 1

When there is a file called “chap0[1-5]” in the same directory.

wc (Word Count) will display the lines, words and characters of a file.

Question 2

Is ‘>foo < bar sort’ a legitimate Unix command, and what does it appear to do?

Answer 2

No it is not. >foo is an Invalid Null Command.

But it appears to write Null to ‘foo’, then send the contents of ‘bar’ to ‘foo’ and sorting it.

Question 3

What happens when you execute (i) cat > foo if foo contains data, (ii) who&raquo_space; foo if foo doesn’t exist?

Answer 3

Executing cat > foo will overwrite foo, and who&raquo_space; foo will create foo if it does not exist.

If foo does exist&raquo_space; will append the data to the end of foo.

Question 4

When executing the following two Unix commands: sort filename and sort

Answer 4

The different errors come from who is opening the file. sort or the shell (in the case of

Question 5

How do the commands wc foo and wc < foo differ?

Answer 5

In ‘wc foo’ foo is opened by wc.

In ‘wc < foo’ foo is opened by the shell and redirected to wc.

Question 6

You want to concatenate two files, foo1 and foo2, but also insert some text after foo1 (but before foo2) from the terminal. How will you do this?

Answer 6

UNKNOWN

Question 7

How do you redirect each of the standard output and standard error to two different files in the Bourne-shell and C- shell? Give an example.

Answer 7

Bourne-shell: cat foo bar 2> error_file

C-shell: (cat foo bar > output_file) >& error_file

Question 8

How do you redirect each of the standard output and standard error to the same file in the Bourne-shell and C-shell? Give an example.

Answer 8

Bourne-shell: cat foo bar > output_and_error_file 2>&1

C-shell: cat foo bar >& output_and_error_file

Question 9

How do you redirect the standard input from a file in the Bourne-shell and C-shell? Give an example.

Answer 9

The redirect input symbol, <, instructs the shell to redirect a command’s input from the specified file instead of from the keyboard.

Question 10

What will you get if you execute ls 1> out.file in Bourne-shell and in C-shell? Explain.

Answer 10

Bourne-shell: You will overwrite out.file with the output of ‘ls’. (as bourne-shell treats 1> as >)

tcsh: 1 not found, create empty out.file

Question 11

Display lines 30 through 40 of the file poem on your screen. Assume that the file poem has more than 40 lines.

Answer 11

head -30 poem

Question 12

Print the 5th line in a file called input_file.

Answer 12

head -5 input_file | tail -1

Question 13

How do you select from a file: (i) lines 5 to 10, (ii) second-to-last line?

Answer 13

NOT SURE

tail -2 letter.txt | head -1

Question 14

How does head display its output when used with multiple filenames?

Answer 14

In order of the provided file names, using ==> foo <== as titles.

Question 15

What is the file /dev/null used for?

Answer 15

A virtual file that is always empty and used to dispose of unwanted data. Basically a black hole.

Question 16

How do you find out the number of (i) users logged in (ii) directories in your home directory tree?

Answer 16

who | wc -l

ls -d -l */ | wc -l

Question 17

Consider the Unix command ls -lrt | tee > newfile; Why does this command not produce any output on the screen? Give the command that uses tee correctly (save the output to newfile).

Answer 17

It doesn’t produce any output because you don’t use the redirect > with tee. To have it write both to stdout and a new file you need to do.

ls -lrt | tee newfile

Question 18

In a Bourne-shell, what do the following commands mean? Are they equivalent? Explain.
cat 1> letter 2> save < memo
letter 2> save cat

Answer 18

The first command opens (or creates) the file letter then outputs the error message with save and inputs ‘memo’ before the error message.

The second command differs slightly by printing out the error, and saving ‘cat’ instead of ‘memo’ within the file save.

Question 19

Print the names of all files in the current working directory to the screen in upper case (i.e., translate all lower case characters to upper case). Hidden files should be included.

Answer 19

ls -a | tr a-z A-Z

Question 20

How do you convert a content of a file to uppercase letters?

Answer 20

tr a-z A-Z < filename > newfilename

Question 21

How do you convert a content of a file to lowercase letters?

Answer 21

tr A-Z a-z < filename > newfilename