![]() Unknown to its existence, Doug Mcllroy asked Thompson to specify such a function. ![]() Brief History of grepīefore it was titled, grep was a confidential utility specified by Ken Thompson to find files for several patterns. It comes in handy when we need to filter large log files. The grep command applies a solid non-deterministic algorithm. The pattern is restricted regular expressions in the format of the egrep or ed command. ![]() The pattern is called the regular expression that is found inside the file. The grep command assumes stdin when no files are mentioned. A collating order may specify equivalent classes in character ranges for use. In an expression like, the minus sign (-) cml describes a range based on the current collating order. Usually, we must enclose the whole pattern in one quotation mark if the pattern parameter is not a common string. Characters should be in quotation marks if they occur in the pattern parameter with a special meaning for the shell. The grep filter finds a file for a specific character pattern and shows every line that includes that pattern. Originally, grep was designed for the Unix operating system, but it became available for every Unix-like system later and a few others like OS 9. The name "grep" comes from the command, i.e., ed, which contains the same effect. It is a command-line utility to search plain-text data groups for lines that are the same as a regular expression. grep command filters the content of a file which makes our search easy. The 'grep' command stands for "global regular expression print". Note that for the -o flag, there is no exclamation mark at the end of the output.Next → ← prev Grep Command in Linux/Unix with Examples Last but not least, we use the -o flag to print the matched pattern itself, i.e., Educative. ![]() Searching for Zub would not yield any results because the -n flag runs a case-sensitive search. Additionally, we use the -n flag to print the line number of the line, which contains EDUcative and zub. Subsequently, we use the -i flag to run a case-insensitive search for the sub-string EDUCative in our text file and print the string which contains it. In the example below, we use the echo command to create a text file, and write Educative!, Edpresso, and Sadzub on lines 1, 2, and 3, respectively. The -help flag is used to open the manual page of grep, which contains additional information about it. The ^ operator is used to output all those lines in file.txt which have pattern as their first word. The -v flags invert the search results, as it displays those strings in file.txt which do not contain pattern. The -n flag outputs the line number of the lines containing pattern alongside the line itself. The o flag displays only the matched pattern instead of displaying the entire string or line which contains it. The -w flag is used to output all those lines in file.txt containing pattern as a whole word and not as a sub-string. The -l flag outputs the name of all those files containing text with the word pattern in it as a string or sub-string. It displays all the lines in file.txt that contain the word paTTern, regardless of the alphabetical case as a string or sub-string. The -i flag makes sure that grep performs a case-insensitive search. The -c flag is used to output the number of lines in file.txt that contain the word pattern as a string or sub-string. In this shot, we go through the most frequently used arguments for grep. Users can select a functionality of their choice by setting the right flags or arguments. The grep command supports many functionalities. The GNU Core-utilities package is available on all Unix-like operating systems. The grep command is part of the GNU Core-utilities package and filters text files for a given character arrangement or pattern.
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