grep egrep fgrep difference

1. What is the difference between grep Egrep and Fgrep?
2. Which is faster grep or Egrep?
3. Is Egrep deprecated?
4. What is difference between grep and find?
5. What does grep command do?
6. Why grep is fast?
7. Which grep command will display the number which has 4 or more digits?
8. What is unique command explain with example?
9. Does grep use regex?
10. How do I grep an entire directory?
11. How do you grep for not matching?

What is the difference between grep Egrep and Fgrep?

grep command always uses the modified version of Commentz-Walter algorithm which has worst case O(mn) complexity. fgrep command interprets the PATTERN as a list of fixed strings separated by newlines. But grep always interpreted as regular expressions.

Which is faster grep or Egrep?

Note: The egrep command used mainly due to the fact that it is faster than the grep command. The egrep command treats the meta-characters as they are and do not require to be escaped as is the case with grep. ... Options: Most of the options for this command are same as grep.

Is Egrep deprecated?

egrep is the same as ' grep -E '. fgrep is the same as ' grep -F '. Direct invocation as either egrep or fgrep is deprecated, but is provided to allow historical applications that rely on them to run unmodified.

What is difference between grep and find?

The main difference between the two is that grep is used to search for a particular string in a file whereas find is used to locate files in a directory, etc. ... Grep searches for a string within the file, where find searches the directory tree for a file name that matches the arguments on the command line.

What does grep command do?

grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command g/re/p (globally search for a regular expression and print matching lines), which has the same effect.

Why grep is fast?

GNU grep is fast because it AVOIDS LOOKING AT EVERY INPUT BYTE. GNU grep is fast because it EXECUTES VERY FEW INSTRUCTIONS FOR EACH BYTE that it does look at. ... GNU grep uses raw Unix input system calls and avoids copying data after reading it. Moreover, GNU grep AVOIDS BREAKING THE INPUT INTO LINES.

Which grep command will display the number which has 4 or more digits?

Specifically: [0-9] matches any digit (like [[:digit:]] , or \d in Perl regular expressions) and 4 means "four times." So [0-9]4 matches a four-digit sequence.

What is unique command explain with example?

The uniq command in Linux is a command line utility that reports or filters out the repeated lines in a file. In simple words, uniq is the tool that helps to detect the adjacent duplicate lines and also deletes the duplicate lines. ... txt which contains repeated lines that needs to be omitted.

Does grep use regex?

Grep Regular Expression

A regular expression or regex is a pattern that matches a set of strings. ... GNU grep supports three regular expression syntaxes, Basic, Extended, and Perl-compatible. In its simplest form, when no regular expression type is given, grep interpret search patterns as basic regular expressions.

How do I grep an entire directory?

To include all subdirectories in a search, add the -r operator to the grep command. This command prints the matches for all files in the current directory, subdirectories, and the exact path with the filename.

How do you grep for not matching?

1 Answer. Just as -L searches for contents of a file without a match, -l searches for the contents of a file with a match. So you will need to specify the -l flag in the second "grepping." Additionally, you will need to direct the output of the first grep to the second as command line arguments.