Thompson built grep to assist one of his colleagues at Bell Labs. He helped create Unix, popularized its modular approach, and wrote many of its programs including grep. Ken Thompson has made some incredible contributions to computer science. ![]() The interesting story behind creation of grep This is the official narrative, but you may also see it described as Global Regular Expression ( Processor | Parser | Printer). It is much faster at searching large files. It performs a global research for a regular expression and prints it. The grep command does what the g/re/p commands did in the editor. In which, the input g/re/p performed a global (g) search for a regular expression (re), and subsequently printed (p) any matching lines. ![]() This is at least partially true, but it depends on who you ask.Īccording to reputable sources, the name is actually derived from a command in a UNIX text editor called ed. With its unusual name, you may have guessed that grep is an acronym. It is used for finding a search patterns in the content of a given file. Grep is a command line utility in Unix and Linux systems. In this explainer article, I'll tell you what is grep command and how does it work. ➜ grep -n -w "dfff" test6.If you use Linux for regular work or developing and deploying software, you must have come across the grep command. In the second example, we used multiple grep commands and pipes to match lines containing both “dfff” and “apple” words in the file test6.txt. ➜ grep -n -w -e "dfff" -e "apple" test6.txt In the first example, we use the grep -e option to match the line containing the word “dfff” or “apple” in the file test6.txt. * Match file containing keyword1 or containing keyword2 … : OR * Match file containing keyword1 and containing keyword2 … : AND But matching multiple keywords has two meanings: Grep matches multiple keywords, which we often use on a daily basis. Sometimes, however, we also need to count the keyword to appear in the file, at the same time, according to the line number in reverse order. In the example above, we can count the number of lines or the total number of occurrences of a keyword in a file. In the following example, the grep directory contains files whose filenames contain the keyword “test”, and we use the ls command, pipe, and wc command to count the number of files whose filenames contain the keyword “test” in the directory. ![]() ![]() Grep count the number of files in the directory whose filename contains the specified keyword w, -word-regexp The expression is searched for as a word (as if surrounded by `]' see re_format(7)). o, -only-matching Prints only the matching part of the lines. In the following example, we use grep -w to count the number of times of the string “dfff” in the file ➜ grep -o -w "dfff" test6.txt | wc -l Options: Grep counts the number of times of the specified content in a file You can also use the grep command, pipe, and wc command to achieve the same effect as the grep-c option in the following example. Using grep -c options alone will count the number of lines that contain the matching word instead of the number of total matches. In the following example, we will use the grep command to count the number of lines in the file test6.txt that contain the string “dfff” ➜ grep -c "dfff" test6.txt Grep counts the number of lines in the file that contain the specified content
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