This set of Unix Multiple Choice Questions & Answers (MCQs) focuses on “Unique and tr Command”.
1. Which command is used for locating repeated and non-repeated lines?
a) sort
b) uniq
c) cut
d) paste
View Answer
Explanation: When we concatenate or merge files, we can encounter the problem of duplicate entries creeping in. UNIX offers a special command (uniq) which can be used to handle these duplicate entries. We can also use the sort -u command for doing the same piece of work.
2. uniq command requires a sorted file as input.
a) True
b) False
View Answer
Explanation: uniq command is used for locating repeated and non-repeated entries. But the most important requirement for using uniq command is, the file should be sorted. For example,
$ sort dept.lst | uniq - uniqlist // output in uniqlist
3. Which option is used with uniq command for selecting non-repeated lines?
a) -i
b) -c
c) -u
d) -a
View Answer
Explanation: To select unique lines, we can use the sort -u command. But uniq also offers an option (-u) which is used for selecting non-repeating entries in a field. For example,
$ cut -d “|” -f3 emp.lst | sort |uniq -u // cut 3rd field from emp.lst, sort it and find unique entries
4. Which option is used for selecting repeated entries?
a) -d
b) -c
c) -u
d) -a
View Answer
Explanation: The -d option when used with uniq command lets us select only one copy of duplicate entries. For example,
$ cut -d “|” -f3 emp.lst | sort |uniq -d d.g.m // only single copy of all duplicate entries director executive g.m. manager
5. ______ option is used for counting frequency of occurrence.
a) -d
b) -c
c) -u
d) -a
View Answer
Explanation: We can use the -c option with uniq command to count the frequency of occurrence of all lines along with the lines. For example,
$ cut -d “|” -f3 emp.lst | sort |uniq -c 1 d.g.m 2 director 4 executive 4 g.m. 2 manager
6. The output of the following command will be:
$ uniq foo1 foo2
a) erroneous
b) output stored in foo2
c) concatenates both files
d) process foo1 and output is stored in foo2
View Answer
Explanation: Like sort command, uniq command also accepts the output filename as an argument, but without using -o option. If we use the above command, it will simply process fo1 and overwrites foo2 with its output.
7. Which command is used for translating characters?
a) sort
b) trans
c) tr
d) paste
View Answer
Explanation: The translate (tr) filter is used for manipulating individual characters in a line. Usually, tr command translates characters using one or two compact expressions. The syntax for using tr command is,
$ tr options expression1 expression2 standard input
8. To replace | with ~, which one of the following commands will be used?
a) tr ‘|\’ ‘~-‘
b) tr ‘|\’ ‘~-‘ > emp.lst
c) tr | ~ emp.lst
d) !
View Answer
Explanation: The translate (tr) filter is used for manipulating individual characters in a line. It replaces the first character in the first expression with the first character in the second expression.
9.
head -n 3 emp.lst | tr ‘[a-z]’ ‘[A-Z]’
Above command will change the case of text from lower to upper.
a) True
b) False
View Answer
Explanation: Since we know that tr command doesn’t accept the filename as an argument, the input has to be redirected from a file or a pipe. Above command will change the case of first three lines of emp.lst from lowercase to uppercase.
10. Which option is used with tr command for deleting characters?
a) -d
b) -c
c) -n
d) -a
View Answer
Explanation: By using tr command we can delete the characters from a file. To perform this operation, we’ve to use -d option. For example,
$ tr -d ‘|/’ < emp.lst |head -n 3 //deletes | and / from the first three lines
11. ______ option is used for compressing multiple consecutive characters.
a) -d
b) -c
c) -n
d) -s
View Answer
Explanation: tr command can also remove multiple consecutive characters from a line by using -s option. This will make the line squeeze from multiple consecutive occurrences of a character to a single character. For example, to squeeze multiple contiguous spaces use the following command:
$ tr -s ‘ ‘ < emp.lst | head -n 3
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