How does fgrep work

Displays the entire paragraph containing matched lines. Paragraphs are delimited by paragraph separators, as specified by the Separator parameter, which are patterns in the same form as the search pattern. Lines containing the paragraph separators are used only as separators; they are never included in the output.

The default paragraph separator is a blank line. Suppresses all writing to standard output, regardless of matching lines. Exits with a 0 status if an input line is selected. Running fgrep is the same as running grep with the -F option. Home Help Linux. Description Syntax Examples Related commands Linux commands help. Was this page useful? Precede each line by the block number on which it was found. If you want more complex search, you need to use extended regular expression.

See the difference between basic and extended regex. The fgrep command on the other hand works on fixed string instead of a regex. This means that it takes the search pattern as it is for searching and thus it is faster than grep.

Although, you may still see egrep and fgrep in the wild, their status is deprecated. Many systems still include the binaries for these variants. These flags help standard grep emulate the functionality of each respective command.

This is the standard version of grep designed for searching patterns using basic regular expressions. Using grep requires escaping meta-characters to generate the expected behavior. Suppose I want to search for either tast or test. This is what I can use:. Notice how you have to escape the parenthesis? This is much easier to look at and understand with extended regex. Egrep was created to provide extended support for meta-characters. This means that it escapes these special characters by default.

This saves time and generally makes the expressions easier to read. This can result in unexpected behaviors. Software professionals know that even as computational capability has increased profoundly, optimization can never be ignored.

Grep is a very powerful tool, but it can sometimes use system resources unnecessarily. This is where the idea of fixed grep came from. This software is ideal for use cases where you need to match an exact string. It does not feature the powerful expression tools of the other grep variants.