Agrep Tutorial R

It can also handle Unicode. Grep is the most powerful command in Linux used most commonly. grep wird häufig zusammen mit anderen Befehlen verwendet, um nicht benötigte Informationen vor der Ausgabe auszufiltern. Entries that are about other people or things, but which happen also to mention something about Gerald R. A text file of Barack Obama's tweets is loaded from RFunction. The grep part of this code will output the full string, then we pass that data onto awk which we used it to print only the first and second fields. agrep searches the input file names (standard input is the default) for records containing strings which either exactly or approximately match a pattern. There are four main families of functions in stringr: Character manipulation: these functions allow you to manipulate individual characters within the strings in character vectors. md; The grep command syntax in Linux / Unix. 0 ist ne Null, hat offenbar nen Bug. You are welcome to join our group on Facebook for questions, discussions and updates. grep command filters the content of a file which makes our search easy. This is best exemplified by the incredible functionality offered by the apply. Grep is useful for searching command line output for a certain phrase or regular expression. Learn how grep command search a specified string in a specified location along with grep syntax, and regex. The grep, grepl, regexpr and gregexpr functions are used for searching for matches, while sub and gsub for performing replacement. Due its varying functionalities, it has many variants including grep, egrep (Extended GREP), fgrep (Fixed GREP), pgrep (Process GREP), rgrep (Recursive GREP) etc. You can Submit a program (but not Nominate it) by clearly stating that. I recently switched from MS-Windows XP to Ubuntu Linux. This tutorial is quite unique because it not only explains the regex syntax, but also describes in detail how the regex engine actually goes about its work. If you want tutoring/training in Shiny or need help with building a Shiny app, I'm available for hire. , Chambers, J. In addition to all the above PowerShell also supports the quantifiers available in. mkdir -p dir/dir1 echo "Linux_rgrep" > dir/dir1/rgrep. grep 'istic ' 072. Active 2 months ago. Department of Statistics and Actuarial Science (SAS). It is like Windows, Mac, Android, etc. Dear list, This is my first time trying to set up the development version of R (R-devel ) in my local machine to test. agrep for approximate matching. If you want to learn more on the data. To Read File line by line in Bash Scripting, following are some of the ways explained in detail. There can be zero or more input filenames. One returns indices vector and the other returns a logical vector. The R documentation claims that the default flavor implements POSIX extended regular expressions. It uses a fast sequential algorithm based on bit registers and few simple operations such as “or,” “shift,” and “and. Grep advanced usage. What am I supposed to open in PortView File>Source to allow me to work with what I installed with PortBase?. The 'grep' command is used to search a given file for patterns specified by the user. * sed ist ein Stream-Editor. Netstat is used to display active TCP connections and related listening ports in the computer or system. Unix Command-line Text-Manipulation. Agrep: an approximate Grep. Create a table with id numbers for vec55, and then manually create a reference to the id's in vec55 in vec91. shift and unshift do the same thing to the left end of an array that pop and push do to the right end. My Constraint Programming Blog This is my blog about constraint programming and related paradigms, e. The grep, grepl, regexpr and gregexpr functions are used for searching for matches, while sub and gsub for performing replacement. lets see an example of row bind in R. If the final byte of an input file is not a newline, grep silently supplies one. Description Of H. Wakid and X. Available with a choice of Ubuntu, Linux Mint or Zorin OS pre-installed with many more distributions supported. FindPage-- find content or explore the wiki / | 0. grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Why another variant? As you can see, its just one single RegExReplace() call (I love this stuff) and thus makes it different to all other greps under AutoHotkey. -L, --files-without-match Suppress normal output; instead print the name. This tutorial teaches you all you need to know to be able to craft powerful time-saving regular expressions. --help Display a brief help message and exit. Sed (Stream EDitor) is a useful tool for making substitutions in a text file. Tutorial This section provides some examples of the different kinds of modules you can build with the LLVM makefile system. I would like to choose rows based on the subsets. Developed 1989-1991 by Udi Manber, Sun Wu et al. --no-index Search files in the current directory that is not managed by Git. * grep -E = egrep * grep -F = fgrep * agrep führt fehlertolerantes Suchen durch, während zgrep für Suchen in komprimierten Archiven gedacht ist. The shell is a command interpreter. bz2; freebsd-binutils-2. The egrep command is an extended grep, supporting more RE metacharacters. It is very useful while searching for strings in Unix and Linux operating system. R is not the only way to process text, nor is it always the best way. frame, but with more user friendly printing, subsetting, and factor handling. In this article let us review 15 practical examples of Linux grep command that will be very useful to both newbies and experts. 0 and later, the default regex engine is a modified version of Ville Laurikari's TRE engine. ctags安装和配置首先要说的是ctags是一个linux上很普遍的源码分析工具,可以将代码中的函数变量等定义的位置记录在一个名称为tags的文件. In our context, it usually means a "Unix Shell" in a terminal app, or the ADB shell on a computer to interact with an Android device. Functions in R Programming is a block of code or some logic wrapped inside the curly braces { }, which performs a specific operation. A Tutorial on Loops in R - Usage and Alternatives Discover alternatives using R's vectorization feature. and Wilks, A. grep wird häufig zusammen mit anderen Befehlen verwendet, um nicht benötigte Informationen vor der Ausgabe auszufiltern. 2 , because traditional grep lacked a -q option and its -s option behaved like GNU grep's -q option. Category : Home > Unix Commands. Using regular expressions. You must mean that your ancient Unix doesn't have GNU grep, right? If you do have a modern "grep", just go do a "man grep"; you don't need to read this (though you may want to just so you really appreciate GNU grep). I love grep command on Linux, it helped to search and filter strings easily, always wonder what is the equivalent tool on Windows, and found this findstr recently. There are four main families of functions in stringr: Character manipulation: these functions allow you to manipulate individual characters within the strings in character vectors. txt) or view presentation slides online. In the example below seq 9 generates a list of numbers from 1 to 9, one per line, and grep prints a single matching line: seq 9 | grep 5 # 5 The -C n option (or --context=n in long form) prints n lines before and after each matching line, in addition to the matching line itself:. You are welcome to join our group on Facebook for questions, discussions and updates. 1 patch for problem | with NEW operator causing program aborts. TRE agrep is more powerful than Wu-Manber agrep since it allows weights and total costs to be assigned separately to individual groups in the pattern. Okay, this is the thread to Submit and/or Nominate and/or Second programs for consideration to be included in the 2009 Pricelessware list. Ambil 2 gr larutan larutan agrep, dan tambahkan air keran sampai volume larutan menjadi 1 liter. Pattern Matching and Replacement Description. R agrep function examples, R agrep usage. Then when you want to search all of the files, it only runs its equivalent of grep (agrep) on the files that contain the words you're looking for. It serves as a textbook, a manual for self-study, and a reference and source of knowledge on shell scripting techniques. I guess it filter 'AGGATTACGTGGCGAT' out in raw fastq, but below command doesn't work. grep -r -e "FIND" /DIRECTORY/ Grep Variants. Ne donnez jamais vos paramètres de connexion (identifiant et mot de passe). pol logger: Tripwire: MD5 : 769c0308bcbf747a11f9011f4207dd1e /opt/tripwire/etc/tw. GNU grep, the most popular version of grep on Linux, uses both a text-directed and a regex-directed engine. Learning Regular Expressions. If you are a teacher, academic, manager or trainer and wish to use this material in your classes or training you are more than welcome to link to these pages and refer your students here or show them in your classes, but please do not just copy my material. * grep -E = egrep * grep -F = fgrep * agrep führt fehlertolerantes Suchen durch, während zgrep für Suchen in komprimierten Archiven gedacht ist. A Beginner Guide to String Pattern Matching in R by Regular Expression Part 2; A Beginner Guide to String Pattern Matching in R by Regular Expression Part 1. how do I grep in R? Ask Question Asked 8 years, 9 months ago. In this article, you'll learn about vector in R programming. Output control:-B, --best-match Only output the best matching records, that is, the records with the lowest cost. org 2007/03/11 19:02:38 Modified files:. Win95 doesn't ship with a finger client, but NT does. agrep(vec55[7],vec91,value=T) I think you may be a bit SOL for some of these and perhaps creating an index from scratch is the best bet. grep generally does not work very well for doing a positive and a negative search in one invocation. grep 'istic ' 072. Package: aac-enc Source: fdk-aac Version: 0. It is one of the most widely used and powerful commands on Linux and Unix-like operating systems. You are welcome to join our group on Facebook for questions, discussions and updates. The basic R syntax and the definitions of the two functions are as follows:. It also supports logical operators and is thus ideally suited to automating the search for many of the following flaws. , Chambers, J. The grep command glo-bally searches for regular expressions in files and prints all lines that contain the expres-sion. R Regular Expression. Examples, tips and practice activities. It aims to fill gaps in how regex information is presented elsewhere, including the major regex books. rpm 2007-10-13 17:23 50K AllegroOGG-1. grep, grepl, regexpr, gregexpr and regexec search for matches to argument pattern within each element of a character vector: they differ in the format of and amount of detail in the results. Use the Rdocumentation package for easy access inside RStudio. python3-problem-report/bionic-updates,bionic-updates,now 2. Information retrieval from a phoneme time series database. Package: acct Description-md5: b24f45ef7d67937aa65ecb8e36a7e5a1 Description-zh_CN: 处理进程和用户登录的 GNU 计帐工具 GNU记帐工具(GNU Accounting. A record is by default a single line, but it can be defined differently using the -d option (see below). The free Regular-Expressions. It can also handle Unicode. Package: 0ad-dbg Description-md5: a858b67397d1d84d8b4cac9d0deae0d7 Description-ja: Real-time strategy game of ancient warfare (debug) 0 A. Search for a pattern in current directory: grep -w : match exact word grep -i : ignore case grep -v : Dont mach this grep -r "string" directory. In an attempt to adhere to the DRY principle, this article will focus on just three topics: R's basic regex commands, search and replace in R and R Studio's implementation of regex. Example - Using While Loop. grep -r -e "FIND" /DIRECTORY/ Grep Variants. It is so ubiquitous that the verb "to grep" has emerged as a synonym for "to search. 3-- Flexibly reshape data: a reboot of the reshape package R-cran-rgdal-1. Once you have added this information, save it, and minimize the window. The fgrep command, called fixed grep, and sometimes fast grep. Linux tutorial provides basic and advanced concepts of Linux. In other implementations, basic regular expressions are less powerful. In this mode, grep will perform its search recursively. Agrep supports "windowing" so it can look for routines, and subroutines. you definitely don't need two agrep's but only one, from the indices you can get the equivalent entries. To become an Rmaster, you must practice every day. sudo apt-get remove --auto-remove tre-agrep. 17 Jul, 2012 Previous. How to use grep command Grep is extremely simple to use, I have a text file on my Desktop with the following text. table's fast order in more detail in the data. Tutorial r Analisis Ragam Anova Satu. DCS 0 + r/Pt/ ST already ignored? Using CTRL-L to add a character to the search string that contains \v, punctuation is repeated. Introduction to String Matching and Modification in R Using Regular Expressions Svetlana Eden March 6, 2007 1 Do We Really Need Them ? Working with statistical data in R involves a great deal of text data or character strings. agrep(vec55[7],vec91,value=T) I think you may be a bit SOL for some of these and perhaps creating an index from scratch is the best bet. Linux/Unix Tutorial. In this article, I will share some of my favorite "grep" examples on Linux, and how to "port" it to Windows with "findstr" command. The 'grep' command stands for "global regular expression print". Starting with Perl 5. 33) [universe] Command line utility for searching the Debian package database ara-byte virtuelles Paket, bereitgestellt durch ara. NET regular expressions. DCS 0 $ r Pt ST should be ignored. The typeset command also works in ksh scripts. Direct invocation as either egrep or fgrep is deprecated, but is provided to allow historical applications that rely on them to run unmodified. 1089, To Codify Without Substantive Change Laws Related To Transportation And To AGREP: Permanent Inventory Of Agricultural Research Projects. en construcciÓn. Tutorial on File and Directory Permissions (Unix Power Tools) execute permission without: 50. February 26, 2015. FreeBSD port maintainers Aleksandr A Babaylov <. Explore the example lists: Wes Anderson, Game of Thrones, GitHub how to get to know a list; Introduction to map(): extract elements name and position shortcuts, type-specific and simplifying map. On Windows, if shell_exec does NOT return the result you expected and the PC is on an enterprise network, set the Apache service (or wampapache) to run under your account instead of the 'Local system account'. Approximate String Matching (Fuzzy Matching) Description. md - Search and display the total number of times that the string 'nixcraft' appears in a file named frontpage. 20000824; [email protected] Use the correct macros for `', ``'', and []. The grep command belonging to the Unix family is one of the most versatile and useful tools available. Estimated reading time: 3 minutes Table of contents. agrep(vec55[7],vec91,value=T) I think you may be a bit SOL for some of these and perhaps creating an index from scratch is the best bet. rstatist (xap1) R - a system for statistical computation and graphics. , Chambers, J. agrep search a file for a string with approximate matching. To include the filename use the option -h. txt | grep -v '2' The R equivalent of that would be: grep("2", grep("A|B", vec1, value = T), invert = T). It aims to fill gaps in how regex information is presented elsewhere, including the major regex books. I would like a function similar to agrep that only returns the best match, or best matches if there are ties. 16_1-- 0verkill is a bloody 2D action deathmatch-like game in ASCII-ART 2bsd-diff-2. The grep utility is a powerful tool and can use regular expressions. agrep for approximate matching. Java Project Tutorial - Make Login and Register Form Step by Step Using NetBeans And MySQL Database - Duration: 3:43:32. All function and argument names (and positions) are consistent, all functions deal with. If it encounters a directory, it will traverse into that directory and continue searching. There are two files jcall. txt" it simply searches in all files *. memory compile sizes. Make sure that we enter PHASE_ESTABLISH when we need to. grep command is used to search the content from one or more files based on the pattern. Emacs Lisp objects can be passed to Java code and Java objects can be passed to Emacs Lisp. A "command line" is a text interface to enter commands interactively. grep is a powerful file pattern searcher that comes equipped on every distribution of Linux. Use the correct macros for `', ``'', and []. Just add "-r" (with perhaps --include) and grep will search through subdirectories. Don't worry, it will still contain it's distinctive humor and flair. Getting Finger Information Via Telnet By now, you've probably heard or read a lot about finger. rstatist (xap1) R - a system for statistical computation and graphics. Vous devez être la seule personne à en avoir connaissance. In the example below seq 9 generates a list of numbers from 1 to 9, one per line, and grep prints a single matching line: seq 9 | grep 5 # 5 The -C n option (or --context=n in long form) prints n lines before and after each matching line, in addition to the matching line itself:. Grep is a tool used to search for specified patterns within text input using regular expressions. This is my first message at R-helpso I'm hoping I have some beginner's luck and get some good help for my problem! FYI I have just started using R. grep, egrep, and fgrep. I create a file called 123. 3 server, you can use. The grep part of this code will output the full string, then we pass that data onto awk which we used it to print only the first and second fields. For brevity, references are numbered, occurring as superscript in the main text. Perl 6 is a sister language, part of the Perl family, not intended as a replacement for Perl 5, but as its own thing - libraries exist to allow you to call Perl 5 code from Perl 6 programs and vice versa. , Chambers, J. Above example won't follow any symbolic link. ctags安装和配置首先要说的是ctags是一个linux上很普遍的源码分析工具,可以将代码中的函数变量等定义的位置记录在一个名称为tags的文件. agrep search a file for a string with approximate matching. Drop unexpected PAP/CHAP packets (if not in NETWORK or ESTABLISH phase). Check man git-grep for help. Grep Command In Unix With Example Grep searches input files for lines containing a match to a given pattern list. How to use grep command Grep is extremely simple to use, I have a text file on my Desktop with the following text. md - Search and display the total number of times that the string 'nixcraft' appears in a file named frontpage. Typically, regex patterns consist of a combination of alphanumeric characters as well as special characters. grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. 2-3) [universe] 3D rendering solution adhering to the RenderMan(R) standard, examples ara (1. ", } @ARTICLE{Burr94:Comparison, AUTHOR="W. In GNU grep there is no difference in available functionality between basic and extended syntaxes. mkdir -p dir/dir1 echo "Linux_rgrep" > dir/dir1/rgrep. So, let us explore R Switch statement here. png',and I use the command 'grep -r switchdesk. Linux Command Line Dictionary. Steve (who attended my "Power through your work with InDesign Styles" seminar in September) wrote: "I am trying to find an InDesign GREP style that would find select every character (paragraphs included) between any amount of tabs and the next instance of a bullet. Both functions need a pattern and an x argument, where pattern is the regular expression you want to match for, and the x argument is the character vector from which matches should be sought. Daniel Miessler is a cybersecurity expert and author of The Real Internet of Things, based in San Francisco, California. Package: acct Description-md5: b24f45ef7d67937aa65ecb8e36a7e5a1 Description-ko: 프로세스와 로그인 계정을 관리하기 위한 GNU 계정 관리 도구 GNU. A function is a set of statements organized together to perform a specific task. unix is a powerful. If the final byte of an input file is not a newline, grep silently supplies one. Should mention what triggered the change. Linux and Unix xargs command tutorial with examples Tutorial on using xargs, a UNIX and Linux command for building and executing command lines from standard input. ) without worrying about where those URLs came from. Emacs Lisp objects can be passed to Java code and Java objects can be passed to Emacs Lisp. This tutorial is organised as such, with each section building upon the knowledge and skills learned in the previous sections. tolower, toupper and chartr for character translations. This R tutorial on loops will look into the constructs available in R for looping, when the constructs should be used, and how to make use of alternatives, such as R’s vectorization feature, to perform your looping tasks more efficiently. 7_1-- R package for flexibly restructuring and aggregating data R-cran-reshape2-1. You can't mix the size of your corpus (# of keys) with the size of the keys. For example,. So, if you use my stubs file, you probably should set the cino option. Fuzzy String Matching – a survival skill to tackle unstructured information. Egrep command is grep -E version which will extend the functionality of grep and provide regular expression support. But in the same way that the ed command g/re/p became a stand-alone tool named "grep," some of grep's most useful flags eventually spun off into more tools. Distance between strings is measured by the edit distance or one of its variants. In the DOS command window, type: c:\>nbtstat -R This command reloads the cache from the Lmhosts file you just created. tags文件的产出最简单的. There are four main families of functions in stringr: Character manipulation: these functions allow you to manipulate individual characters within the strings in character vectors. External}, so this is now only a minor issue. Department of Statistics and Actuarial Science (SAS). pattern will only be seen as such (and not as an input filename) if it wasn't already specified withinoptions (by using the '-e pattern' or '-f file' options). Distance between strings is measured by the edit distance or one of its variants. Painful, I know, but a lot of it can be done with agrep(). The _ B_ r_ o_ k_ e_ r subsystem retrieves indexing information from one or more Gatherers, suppresses duplicate information, incrementally indexes the collected information, and provides a WWW query interface to it. Available with a choice of Ubuntu, Linux Mint or Zorin OS pre-installed with many more distributions supported. If you want to search symbolic link to then run the following command. The basic R syntax and the definitions of the two functions are as follows:. Package: acct Description-md5: b24f45ef7d67937aa65ecb8e36a7e5a1 Description-zh_CN: 处理进程和用户登录的 GNU 计帐工具 GNU记帐工具(GNU Accounting. In this article, I will share some of my favorite "grep" examples on Linux, and how to "port" it to Windows with "findstr" command. This sort provided such a compelling improvement over R's base::order that the R project adopted the data. Factor is a data structure used for fields that takes only predefined, finite number of values (categorical data). Bash Read File line by line. For example, if you know you entered a command recently that you want to use again, but you just don't want to press up a billion times to find it, you can use grep to search your command history! Here's how it's done: history | grep "find". frame, writing simple loops, and perhaps writing simple functions. Approximate String Matching (Fuzzy Matching) Description. The post is broadly divided into 3 sections. Package 'stringr' February 10, 2019 Title Simple, Consistent Wrappers for Common String Operations Version 1. For example, there's the recursive rgrep, which is the same as grep -r. See Advanced Unix filesystem navigation and NCD clones for more details (in NCD clones find often is used for creation of the list of directories for the whole filesystem or some subtree and stored for future reference. For instance, print, abs(), sqrt() etc. Regular expressions are a system for describing compl. Die Treffer werden unter Angabe der Datei und der Zeilennummer (Option -n) auf der Standardausgabe ausgegeben. This is my first message at R-helpso I'm hoping I have some beginner's luck and get some good help for my problem! FYI I have just started using R. R Regular Expression. I guess it filter 'AGGATTACGTGGCGAT' out in raw fastq, but below command doesn't work. Package: acct Description-md5: b24f45ef7d67937aa65ecb8e36a7e5a1 Description-ko: 프로세스와 로그인 계정을 관리하기 위한 GNU 계정 관리 도구 GNU. It also supports logical operators and is thus ideally suited to automating the search for many of the following flaws. By default, grep prints the matching lines. All Debian Packages in "squeeze" Generated: Sun Nov 6 05:08:31 2011 UTC Copyright © 1997 - 2011 SPI Inc. (?!\p{N})\p{Arabic} This would work in Perl, PCRE (C, PHP, R…) and Ruby 2+. For that type: man. com Outline Conventions in R Data Splitting and Estimating Performance Data Pre-Processing Over-Fitting and Resampling Training and Tuning Tree Models Training and Tuning A Support Vector Machine Comparing Models Parallel. So grep returns all matching lines that contain foo as a substring. Then when you want to search all of the files, it only runs its equivalent of grep (agrep) on the files that contain the words you're looking for. In this Linux/Mac terminal tutorial, we will be learning how to use the grep command. A Tutorial on Loops in R - Usage and Alternatives Discover alternatives using R's vectorization feature. … I'm going to use it as an example. Search the history of over 373 billion web pages on the Internet. , whereas some journal editors would prefer to have Craig, Roy R. GitHub Gist: instantly share code, notes, and snippets. - Wikinaut/agrep. 0 there has a third danger, that objects could be moved in memory by the garbage collector. Exit status is 0 if matches were found, 1 if no matches were found, and 2 if errors occurred. Vaman", TITLE="A Comparison of {FDDI} Asynchronous Mode and {DQDB} Queue Arbitrated Mode. grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. R agrep function examples, R agrep usage. Getting Finger Information Via Telnet By now, you've probably heard or read a lot about finger. There are no current plans to update the Llama. A text file of Barack Obama's tweets is loaded from RFunction. 0-- R Version of GENetic Optimization Using Derivatives. Examples, tips and practice activities. Beginning at the first line in the file, grep copies a line into a. To understand why this example was so straightforward, here is a closer look at the underlying HTML:. agrep() function searches for approximate matches to pattern within each element of the. The grep command used to find a particular string or pattern in one or multiple patterns. rgrep is a recursive version of grep. El programa. shift and unshift do the same thing to the left end of an array that pop and push do to the right end. Mario Dantas Unix-perl - Free ebook download as Powerpoint Presentation (. R grepl Function. grep command is used to search the content from one or more files based on the pattern. unix is great os. Bacteriophages: Practical Applications for Nature's Biocontrol' presents the latest information on uses in healthcare settings as well as animal husbandry, management and care of farm animals by using enhanced phages to replace antibiotics for growth promotion in animal feed or to prevent, control and treat disease in animals. Grep is a tool used to search for specified patterns within text input using regular expressions. It also introduces a subset of packages from the Bioconductor project. A 'regular expression' is a pattern that describes a set of strings. The power of grep comes with using its options and regular expressions. This tutorial will cover how to use regular expressions to explore the power of the 'grep' command. But just for the hell of it, let’s see how often people talk about the two. Introduction to String Matching and Modification in R Using Regular Expressions Svetlana Eden March 6, 2007 1 Do We Really Need Them ? Working with statistical data in R involves a great deal of text data or character strings. This approach allows your cinoptions to be effective, so you get the indentation style you prefer (abbreviations prevent this). com and put into a character vector. This work by Julia Silge and David Robinson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3. Votre mot de passe doit comporter au moins 12 caractères (lettres majuscules, lettres minuscules, chiffres, caractères spéciaux). I would like a function similar to agrep that only returns the best match, or best matches if there are ties. Not Sure If Many People Use This Site, however heres A Few Steps To getting In. are some of the. Netstat is used to display active TCP connections and related listening ports in the computer or system. Java Project Tutorial - Make Login and Register Form Step by Step Using NetBeans And MySQL Database - Duration: 3:43:32. 0, see ?sort and the R Release NEWS. It is one of the most useful commands. Regular expressions are a concise and flexible tool for describing patterns in strings. Invalid regular expression in R using grep() with lookarounds. Due its varying functionalities, it has many variants including grep, egrep (Extended GREP), fgrep (Fixed GREP), pgrep (Process GREP), rgrep (Recursive GREP) etc. Case insensitive search : The -i option enables to search for a string case insensitively in the give file.