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The CORRECT answer is (b) sed -n ‘3,10p’ emp.lst

To EXPLAIN I would say: To select a specific number of LINES, we can USE sed along with p OPTION. For example,

The correct answer is (d) &

Easy explanation: sed SUPPORTS the use of REPEATED PATTERN. For this purpose, & is used. It makes the whole string appear in the target string also. For example, to replace the string Linux with Red HAT Linux, use the following COMMAND:

Right choice is (c) { and }

For explanation I would SAY: Interval regular expression uses { and } with a single or PAIR of NUMBERS between them. For EXAMPLE,

Correct ANSWER is (d) $ and ^

Explanation: We can use the anchoring characters, ^ and & with the same meaning. They are USED as sole characters in the SOURCE pattern to REPLACE the target pattern at that location. For EXAMPLE,

Right answer is (c) sed ‘1,5s/director/manager/’ emp.lst

For EXPLANATION I would say: Performing SUBSTITUTION using sed is not only limited to a single CHARACTER; it can be any STRING. Above command will replace the string ‘director’ with ‘manager’ in the FIRST five lines of file emp.lst.

Correct ANSWER is (B) 3

The BEST explanation: Basic regular expressions are divided into three CATEGORIES namely –repeated pattern, Interval regular expressions and tagged regular expressions.

Right choice is (C) SED‘s/|/:/g’ emp.lst

Easiest explanation: sed can perform SUBSTITUTION i.e. it allows us to replace a pattern in its input with some other pattern. The FLAG g is used for performing substitution globally.

Right ANSWER is (C) sed [address]s/expr1/ expr2/ flags

Best EXPLANATION: Substitution is one of the most IMPORTANT features of sed as it ALLOWS us to replace a pattern in its input with some other pattern. The correct syntax for performing substitution is :

Correct answer is (a) SED -n ‘/gupta/,/agarwal/p’emp.lst

Explanation: Context ADDRESSING allows us to specify ONE or two patterns to locate LINES. To do so, a separate pair of context addresses by a COMMA.

Right option is (a) True

The best I can explain: Substitution is one of the most IMPORTANT features of sed as it ALLOWS us to replace a pattern in its input with some other pattern. For this purpose, regular expressions are used for enhancing pattern MATCHING capabilities.

The correct CHOICE is (C) //

To EXPLAIN: The second form of addressing apart from relative addressing is context addressing. It allows us to SPECIFY ONE or two patterns to locate lines. The pattern must be bounded by a / on either side.

The correct option is (a) True

Explanation: If we want to SELECT the LAST LINE of the file, we can either provide the line number of the file or it is more CONVENIENT to USE $ symbol.

Right ANSWER is (d) –f and -e

For explanation I would say: Both -e and -f allows US to use multiple instructions with SED. For example, -e allows us to ENTER as many instructions as we want, each PRECEDED by the option.

The CORRECT choice is (c) p

Explanation: GENERALLY, ‘p’ is used for PRINTING LINES. However, this command behaves in a strange manner i.e. it both displays and prints the SELECTED lines.So the selected lines will appear twice.

The CORRECT CHOICE is (b) -n

For explanation: When we use ‘p’, it BEHAVES in a strange manner i.e. it both displays and prints the SELECTED lines.So the selected lines will appear TWICE. To suppress this behavior, we use the -n option whenever we use the p command. For example,

Right CHOICE is (c) sed ‘3q’ emp.lst

Easy EXPLANATION: We can use line addressing feature of sed command by using ‘q’ ALONG with the line number. For example, 3q will QUIT after selecting 3 lines from the file. Here ‘q’ is used for QUITTING.

The correct option is (C) -E

The best EXPLANATION: grep command SUPPORTS both categories of regular expressions. It supports basic regular expression by DEFAULT and EXTENDED regular expression with -E option.

The correct answer is (a) sed

To ELABORATE: sed is a MULTIPURPOSE tool which PERFORMS the function of several filters together. This filter is DERIVED from the ed (original UNIX editor). It performs non-interactive operations on a data stream.It uses instructions to act on a text for selecting lines, with an action to be taken.

Right answer is (c) SED options ‘address ACTION’ file(s)

To explain I would say: sed is a MULTIPURPOSE tool which performs the function of several filters together. It can even MANIPULATE characters in the file. The SYNTAX for using this tool is:

sed options ‘address action’ file(s)

Right ANSWER is (d) + and –

Explanation: The ERE set includes two special characters, + and ? which are USED in place of * to RESTRICT the matching scope. They signify the following,

The CORRECT choice is (b) .

The BEST explanation: A (.) matches a SINGLE character. The shell uses ? character to indicate that. The PATTERN g . . . will match a four character STRING beginning a ‘g’. The shell’s equivalent pattern is g???

The correct option is (d) ^ and $

Explanation: Most of the REGULAR EXPRESSION character are USED for matching PATTERNS, but there are two symbols that are used for matching PATTERN at beginning or end of a line. These symbols are ^ and $.

The correct answer is (a) *

To explain: The asterisk (*) refers to the immediately preceding CHARACTER. It can match the previous character which can OCCUR any number of TIMES or not at all. For EXAMPLE, g* can match a null STRING along with g, gg, ggg, gggg and so on.

Correct option is (C) [ ]

The explanation: A REGULAR expression LETS us specify a group of characters enclosed within a pair of rectangular brackets, [ ]. For EXAMPLE, [ra] matches either r or a.

Correct answer is (d) CH+

The BEST I can EXPLAIN: The basic regular expression character subset doesn’t CONTAIN ch+, as it is a part of the extended regular expression.

Correct CHOICE is (b) 2

The best I can explain: POSIX identifies regular EXPRESSIONS as BELONGING to TWO categories i.e. regular and EXTENDED.

Correct answer is (a) True

Easy explanation: If we want to search a single PATTERN or more than one pattern, then we can place them into a FILE with one pattern per line and after that, we can take the pattern for the GREP command from the same file USING -f option. For EXAMPLE,

The correct answer is (a) -v

Explanation: grep can play an inverse role;the -v (inverse) OPTION selects all lines except those CONTAINING the pattern. For EXAMPLE, the FOLLOWING COMMAND.

Correct choice is (d) -l

For explanation I would say: The -l (list) OPTION DISPLAYS only the NAMES of FILES containing the pattern. For example, the following command will display the FILENAMES having an extension .lst and containing the pattern ‘director’:

Correct option is (d) -n

The EXPLANATION is: The -n (number) option displays the line NUMBERS CONTAINING the pattern, along with the lines. For example,

The correct answer is (c) -i

The best EXPLANATION: When we want to SEARCH a pattern using grep COMMAND and we want to ignore the case or we are not SURE of the case, we’ve to use the -i option. This option ignores the case the pattern matching.

Right option is (b) double quotes

Explanation: We’ve to quote the pattern in double quotes when it contains MULTIPLE WORDS or SPECIAL characters else they will be INTERPRETED in some other way by the shell. If the pattern doesn’t contain multiple words, then there is no need for quoting the patter in any quotes. If the pattern contains only multiple words, then we can quote the pattern in single quotes also.

Correct choice is (d) grep“director” emp.lst

To explain: Because grep command is also a filter, it can SEARCH it’s standard input for the PATTERN. For example, the command grep“director” emp.lst will search the FILE emp.lst for the pattern “director” and will display the LINES CONTAINING this pattern.