perlrequick -- Perl regular expression quickstart (2023)



  • Name
  • describe
  • tourist guide
    • simple word pairing
    • Use character classes
    • fits this or that
    • Hierarchical clustering and matching
    • extract matches
    • double match
    • further placements
    • search and replace
    • division operator
    • use re "strict"
  • flee
  • See also
  • Author and Copyright
    • gracias

perlrequick -- Perl regular expression quickstart

This page covers the basics of understanding, creating, and using regular expressions ("regexes") in Perl.

This page assumes you already know a few things, such as: B. what a "mode" is and the basic syntax for using it. If not, check it outperlretut.

#simple word pairing

The simplest regular expression is just a word, or more generally a string. A regular expression consisting of one word matches any string containing that word:

"Hello World" = ~/world/; # Matches

In this statementWeltis a regular expression and//Cerrado/Welt/Tells Perl to look for a match in the string. operator=~Concatenates a string with a regular expression match, returning true if the regular expression matches and false if the regular expression doesn't match. In our example,Weltsecond word in play"Hello World", so the expression is true. There are several variations on this idea.

Expressions like this are useful in conditional statements:

if „Hello World“ = ~/World/, imprime „coincide con \n“;

The meaning of a match can be reversed with!~Operator:

print „Mismatch\n“ if „Hello World“ !~ /World/;

String literals in regular expressions can be replaced with variables:

$greeting = "World";print "Match\n" if "Hello World" =~ /$greeting/;

If you agreePS, It is$_ =~Parts can be left out:

$_ = "Hallo Welt"; print „Match\n“ if /World/;

last but not least,//The default delimiter for the match can be changed by placing it in any delimiter'Metro'before:

"Hello World" =~ m!World!; # match separated by '!' "Hello World" =~ m{World}; # match, look for match '{}'"/usr/bin/perl" = ~ m "/perl"; # After matching "/usr/bin", "/" becomes an ordinary character

The regular expression must match part of the stringExactlyFor the statement to be true:

"Hello World" =~ /world/; # mismatch, case sensitive "Hello World" =~ /o W/; # matches ' ' is a normal character "Hello World" =~ /World /; # does not match, no end ''

Perl always looks for the earliest possible point in the string:

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"Hello World" =~ /o/; # matches 'o' in 'hello' "This hat is red" =~ /hat/; # matches "hat" in "That".

Not all characters can be used in a game "as is". some characters, namedmetacharactersare considered special and reserved for regular expression notation. The metacharacters are


Metacharacters can be joined literally by preceding them with a backslash:

"2+2=4" =~ /2+2/; # does not match, + is a metacharacter "2+2=4" =~ /2\+2/; # matches, \+ is treated as a normal character + 'C:\WIN32' =~ /C:\\WIN/; # matches "/usr/bin/perl" =~ /\/usr\/bin\/perl/; # fit

The slash in the last regular expression'/'Also a backslash as it is used to delimit regular expressions.

Most metacharacters are not always special, other characters (e.g. pattern separators) become special under different circumstances. This can be confusing and produce unexpected results.use re "strict"It can inform you about possible dangers.

Non-printable ASCII characters are represented asescape sequenceA common example is\Tfor labels,\nortefor new lines and\RGot in. Arbitrary bytes are represented by octal escape sequences, for example:\033, or a hexadecimal escape sequence, for example,\x1B:

"1000\t2000" =~ m(0\t2) # corresponds to "cat" =~ /\143\x61\x74/ # corresponds to ASCII, but #cat is misspelled

Regular expressions are mostly treated as double-quoted strings, so variable substitution works:

$foo = 'casa'; 'gathouse' =~ /gato$foo/; # fall with 'housecat' =~ /${foo}gato/; # collapse

For all of the above regular expressions, the regular expression is considered a match if it matches anywhere in the string. indicateWomust match, we will use itAnkermetacharacters^jPS.Anker^means that the beginning of the string and the anchor matchPSmeans match at the end of the string or before a newline at the end of the string. Some examples:

"housekeeper" =~ /keeper/; # matches "housekeeper" =~ /^keeper/; # does not match "housekeeper" =~ /maid$/; # matches "housekeeper\n" =~ /maid$/; # matches "housekeeper" =~ /^housekeeper$/; # Matches

#Use character classes

Acharacter classAllows you to match a range of possible characters at a given location in a regular expression, not just one character. There are many different types of character classes, but generally the use of the term means the types described in this section, which are technically called "parenthesized character classes" because they are specified in parentheses.[...], which contains the set of possible matching characters. However, we will remove the "brackets" below to conform to common usage. Here are some examples of character classes (in parentheses):

/gato/; # matches 'gato'/[bcr]at/; # matches 'murciélago', 'gato' or 'rata' "abc" =~ /[taxi]/; # matches "a".

However, in the final statement'C'is the first character of the class, the first period that the regular expression can match'A'.

/[yY][eE][sS]/; # matches "yes", case insensitive # "yes", "Yes", "YES", etc./yes/i; # also written in a case-insensitive form that matches "Yes".

The last example shows the same thing.'I' modifier, which makes the match case-insensitive.

There are ordinary and special characters within character classes, but the set of ordinary and special characters within a character class is different from the set outside of a character class. Special characters for character classes are-]\^$And use the escape match:

/[\]c]def/; # matches ']def' or 'cdef' $x = 'bcr';/[$x]at/; # matches 'murciélago', 'gato', or 'rata'/[\ $x]at/; # matches '$at' or 'xat'/[\\$x]at/; # matches '\at', 'bat', 'cat', or 'rat'

special character'-'Acts as a scope operator for character classes, making it unwieldy to use[0123456789]j[]lose weight[0-9]j[Arizona]:

/item[0-9]/; # matches 'item0' or ... or 'item9'/[0-9a-fA-F]/; # matches hexadecimal digits

And'-'is the first or last character of a character class, treated like an ordinary character.

special character^First in a character class meansnegated character class, which matches any character except those in parentheses. both[...]j[^...]A single character must match; otherwise the match fails. So

/[^a]in/; # does not match 'aat' or 'at', but does match # all other 'bat', 'cat, '0at', '%at', etc. /[^0-9]/ ; # Matches a non-digit character /[a^]at/; # matches 'aat' or '^at'; here '^' is normal

Perl has shortcuts for several commonly used character classes. (These definitions are used by Perl in Safe ASCII mode/AOtherwise, they can also match more non-ASCII Unicode characters. see"Backslash sequence" in PerlrecharclassLearn more. )

  • \d is a number that represents

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  • \s is a space that represents

  • \w is a word character (alphanumeric or _) representing

  • \D is a negated \d; represents any character except a digit

  • \S is a negated \s; represents any character that is not a space

  • \W is a negated \w; represents any character that is not a word

  • Period'. ' matches any character except "\n"

It is\d\s\w\D\S\WAbbreviations can be used both inside and outside of character classes. Here are some that are in use:

/\d\d:\d\d:\d\d/; # corresponds to hh:mm:ss time format /[\d\s]/; # matches any number or space /\w\W\w/ ; # matches a word char followed by # char that is not a word followed by a word char/..rt/; # matches any two characters followed by 'rt'/end\./; # matches "end". /End[.]/; # same, equals "end".

It isback \BMatches the boundary between a word character and a non-word character\w\WÖ\w\w:

$x = "Housecat combines house and cat";$x =~ /\bcat/; # matches cats in "catenates" $x =~ /cat\b/; # matches cats in 'housecat' $x =~ /\ bcat\b/; # matches "cat" at the end of the string

In the last example, the end of the string is considered a word boundary.

Use for natural language processing (e.g. words with apostrophes) instead.\b{wb}

"no" = ~/.+? \b{wb} /x; # matches the entire string

#fits this or that

We can combine different stringsAlternativemetacharacters'|'.PhosphorDogÖGato, we form the regular expressiondog | Cat.As before, Perl tries to find the regular expression as early in the string as possible. At each character position, Perl first tries to find the first alternative,Dog.AndDogdoes not match, Perl tries the following alternative:Gato.AndGatoNo match, then the match fails and Perl moves to the next position in the chain. Some examples:

"Cats and Dogs" =~ /cat|dog|bird/; # matches "cat" "cats and dogs" =~ /dog|cat|bird/; # matches "cat".

AlthoughDogis the first option in the second regular expression,GatoAbility to match at the beginning of a string.

"cats" =~ /c|ca|cat|cats/; # matches "c" "cats" =~ /cats|cat|ca|c/; # matches "cats"

At a given character position, the first option that allows the regular expression to match correctly is the one that matches. Here all alternatives match at the first position in the string, i.e. the first matches.

#Hierarchical clustering and matching

It isgroupmetacharacters()Allows you to treat part of a regular expression as a unit. Parts of a regular expression are grouped by enclosing them in parentheses. regular phrasehouse (cat | breeder)means coincidenceCasafollowed byGatoÖgoalie.Other examples are

/(a|b)b/; # matches 'ab' or 'bb'/(^a|b)c/; # matches "ac" at the beginning of the string or "bc" anywhere /home(cat|)/; # matches 'house cat' or 'house'/house(cat(s|)|)/; # matches "domestic cat" or "domestic cat" or # "house". Groups of notes can be nested. "20" =~ /(19|20|)\d\d/; # matches the null alternative '()\d\d', # because '20\d\d' cannot be found

#extract matches

group metacharacters()You can also use it to extract matching string parts. For each grouping, the internal match part goes into a special variable1 $,2 $Wait. They can be used as normal variables:

# extract hours, minutes, seconds $time =~ /(\d\d):(\d\d):(\d\d)/; # conforms to the format hh:mm:ss $hours = $1;$minutes = $2;$seconds = $3;

In list context matches/normal Sentence/with groupings returns a list of matching values($1,$2,...).so we can rewrite it as

(Video) Coding 101 23: Perl: RegEx Search and Replace

($hours, $minutes, $seconds) = ($time =~ /(\d\d):(\d\d):(\d\d)/);

If the groupings in the regular expression are nested,1 $Get the leftmost opening parenthesis group,2 $next left parenthesis, etc. For example, here is a complex regular expression and matching variables:

/(ab(cd|ef)((gi)|j))/; 1 2 34

Link to match variable1 $,2 $, ... Andlater reference \g1,\g2, ... backreferences are match variables that can be usedInRegular sentence:

/(\w\w\w)\s\g1/; # Find sequences like "the" in the string

1 $,2 $, ... can only be used outside regular expressions, and\g1,\g2, ... only within regular expressions.

#double match

It isQuantormetacharacters?,*,+, and{}With this we can determine the number of repetitions of the part of the regular expression that we consider a match. The quantifier comes immediately after the character, character class, or grouping that we want to specify. They have the following meaning:

  • A?= matches 'a' 1 or 0 times

  • A*= matches 'a' 0 or more times, i.e. H. any number of times

  • and += matches 'a' 1 or more times, i.e. H. at least once

  • a {n,m}= at least matchnortetimes, but no more thanReissecond rate.

  • like,}= at least matchnorteor more often

  • like}= PartynorteAt least sometimes

  • like}= exact matchnortesecond rate

Here are some examples:

/[a-z]+\s+\d*/; # matches a lowercase word, at least some spaces, and # any number of digits /(\w+)\s+\g1/; # matches double words of any length $year = ~ /^\d{2,4}$/; # Make sure the year has at least 2 but no more # 4 digits $year =~ /^\d{ 4 }$|^\d{2}$/ ; # best match; Discard three-digit dates

These quantifiers try to match as many strings as possible and still allow regular expression matches. so we have

$x = 'the cat in the hat'; $x =~ /^(.*)(at)(.*)$/; # matches, # $1 = 'the cat in h' # $2 = 'at' # $3 = '' (0 matches)

first quantifier.*Get as much of the string as possible while maintaining regular expression matching. second quantifier.*Since there is no more string, it will match 0 times.

#further placements

There are a few other things you might want to know about the match operators. global modifier/ GRAMMThe match operator can match as many times as possible in the string. In a scalar context, consecutive matches are made on strings/ GRAMMJump from one game to the next while keeping an eye on your position in the chain. You can get or set the location withLocation()Function. For example,

$x = "猫狗屋"; # 3 words while ($x =~ /(\w+)/g) { print "word is $1, ends at position", pos $x, "\n";}


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The word is cat, the word ending in position 3 is dog, the word ending in position 7 is house, the word ending in position 13

A failed match or change in the target string resets the position. If you don't want to reset the position after a failed match, add/C, if/regex/GC.

In the context of the list/ GRAMMReturns a list of matching groupings, or if there are no groupings, the full list of regular expression matches. So

@words = ($x =~ /(\w+)/g); # 匹配,# $word[0] = 'cat' # $word[1] = 'dog' # $word[2] = 'house'

#search and replace

Search and replace is done withs/regex/replacement/modifier.It isalternativesis a Perl double-quoted string that replaces strings withregular phrase.Operator=~Also used here to compare stringsfew///.if they agreePS, It is$_ =~can be ruled out. if there is a gamefew///Returns the number of replacements; otherwise false is returned. Here are some examples:

$x = "Time to feed the cat!";$x =~ s/cat/hacker/; # $x contains "Time to feed the hacker!" $y = "'words in quotes'";$y =~ s /^'(.*)'$/$1/; # remove single quotes, # $y contains "quotes"

Withfew///operator, variable to match1 $,2 $etc. They are immediately available for substitution expressions. With the global modifierseconds///gramsfinds and replaces all occurrences of the regular expression in the string:

$x = "I hit 4 of 4"; $x =~ s/4/four/; # $x contains "I hit 4 of 4" $x = "I hit 4 of 4"; $x =~ s/ 4/four/g; # $x contains "I played four against four"

lossless modifiers///rCauses the result of the replacement to be returned and not modifiedPS(or any variable bound by the replacement=~):

$x = "I like dogs.";$y = $x =~ s/dogs/cats/r;print "$x $y\n"; # print “I like dogs. I like cats." $x = "Cats are cool.";print $x =~ s/Cats/Dogs/r =~ s/Dogs/Frogs/r =~ s/Frogs/Hedgehogs /r, "\n" ;# Print " Hedgehogs are cool."@foo = map { s/[a-z]/X/r } qw(a b c 1 2 3);# @foo is now qw(X X X 1 2 3 )

rating modifierTrumpet /// Trumpetwrap oneEvaluate{...}Encloses the replacement string and replaces the result of the evaluation with the matching substring. Some examples:

# reverse all words in string $x = "the cat in the hat"; $x =~ s/(\w+)/reverse $1/ge; # $x contains "eht tac ni eht tah" # convert percentage convert to decimal $x = "A hit rate of 39%";$x =~ s!(\d+)%!$1/100!e; # $x contains "A hit rate of 0.39"

The last example showsfew///Other delimiters can also be used, e.gjfew{}{}, it is includedS{}//.if you use single quotesfew''', regular expressions, and substitutions are treated as single-quoted strings.

#division operator

split/regex/, stringTo shareChainGo to a list of substrings and return that list. regular expression to determine the character stringChainas opposed to division. For example, to split a string into words, use

$x = "Calvin and Hobbes";@word = split /\s+/, $x; # $word[0] = 'Calvin' # $word[1] = 'and' # $word[2] = 'Hobbes '

To extract a comma-separated list of numbers, use

$x = "1.618,2.718, 3.142";@const = split /,\s*/, $x; # $const[0] = '1.618' # $const[1] = '2.718' # $const[2] = '3.142'

if the regular expression is empty//When used, the string is split into individual characters. If the regular expression has groupings, the resulting list also contains matching substrings of the grouping:

$x = "/usr/bin";@parts = dividiere m!(/)!, $x; # $parts[0] = '' # $parts[1] = '/' # $parts[2] = 'usr' # $parts[3] = '/' # $parts[4] = 'bin'

Since the first character of $x matches the regular expression,To shareAdd an empty initial element to the list.

#use re "strict"

New in version 5.22: This enforces stricter rules when compiling regex patterns than would otherwise be possible. You may find things that are legitimate but may not be what you are looking for.


not everyone.

This is just a quick guide. For a more detailed guide on regular expressions, seeperlretutReference pages can be found hereperla.

Copyright (c) 2000 Mark Kvale All rights reserved.

(Video) Learn Regular Expressions In 20 Minutes

This document may be distributed under the same terms as Perl itself.


The authors would like to thank Mark-Jason Dominus, Tom Christiansen, Ilya Zakharevich, Brad Hughes, and Mike Giroux for all their helpful comments.


What is $1 in Perl regex? ›

The $number variables contain the parts of the string that matched the capture groups ( ... ) in the pattern for your last regex match if the match was successful. $1 equals the text " brown ".

What is \d+ in Perl? ›

The /d modifier deletes the characters matching SEARCHLIST that do not have a corresponding entry in REPLACEMENTLIST. For example: #!/usr/bin/perl $string = 'the cat sat on the mat. '; $string =~ tr/a-z/b/d; print "$string\n"; This will produce following result b b b.

How do you start a regex expression? ›

Start of String or Line: ^ By default, the ^ anchor specifies that the following pattern must begin at the first character position of the string. If you use ^ with the RegexOptions. Multiline option (see Regular Expression Options), the match must occur at the beginning of each line.

What is \s+ in Perl? ›

(\S+) | will match and capture any number (one or more) of non-space characters, followed by a space character (assuming the regular expression isn't modified with a /x flag). In both cases, these constructs appear to be one component of an alternation.

What does '$' mean in regex? ›

The $ symbol is one of the most commonly used symbols in RegEx. It is used to match the end of a string. In other words, you can call it "end of line anchor", since it anchors a pattern to the end of the line.

How to match number 1 to 1000 in regex? ›

Use ^(. *[^0-9]|)(1000|[1-9]\d{0,2})([^0-9]. *|)$ which will match 1000 or a non-zero digit followed by up to two further digits. It will also allow other characters on either end of the number.

What is $A and $B in Perl? ›

$a and $b are exempt global variables; they are exempt in that Perl allows them to be used (anywhere) without being declared. They are set by the sort function. Use of any other undeclared global in sort (in strict mode) will trigger an error.

What does \b mean in Perl? ›

\b is the backspace character only inside a character class. Outside a character class, \b alone is a word-character/non-word-character boundary.

What is the difference between $1 and \1 in Perl? ›

In current versions of Perl, \1 and $1 mean different things. Specifically, \1 means "whatever was matched by the first set of grouping parens in this regex match." $1 means "whatever was matched by the first set of grouping parens in the previously-run regex match." For example: /(foo)_$1_bar/

What are regex commands? ›

A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.

What is regex for dummies? ›

Regex, short for regular expressions, is a tool that can be used in just about any programming language. It is based on the mathematical concept of regular sets and regularity. Basically, it is a sequence of characters that are used in search patterns.

How to write a regex code? ›

Creating a regular expression
  1. Using a regular expression literal, which consists of a pattern enclosed between slashes, as follows: const re = /ab+c/; ...
  2. Or calling the constructor function of the RegExp object, as follows: const re = new RegExp("ab+c");
May 5, 2023

What is $_ called in Perl? ›

There is a strange scalar variable called $_ in Perl, which is the default variable, or in other words the topic. In Perl, several functions and operators use this variable as a default, in case no parameter is explicitly used.

What are the 3 categories of Perl? ›

Perl has three basic data types: scalars, arrays, and hashes.

What does \\ s+ mean in regex? ›

The \s (lowercase s ) matches a whitespace (blank, tab \t , and newline \r or \n ). On the other hand, the \S+ (uppercase S ) matches anything that is NOT matched by \s , i.e., non-whitespace.

What does \\ N mean in regex? ›

"\n" matches a newline character.

What does $1 $2 mean in regex? ›

It's the first and the second capturing groups. In regex, you can put a pattern in brackets ( () ). The brackets specify a capturing group: whatever matches in that group is “captured”, and then you can use $1, $2 etc to access the first, second etc groups.

What is $0 and $1 in regex? ›

$0 = the entire matched substring (corresponding to matcher. group()), $1 = the first parenthesized match subpattern (corresponding to matcher.

What is 0 $1 in regex? ›

$0 (or \0 in some languages) is a reference to the match (i.e. it is precisely the first argument to the function), $1 (or \1) is a reference to the first capture group, etc.

How to select 1 character in regex? ›

Match any specific character in a set
  • Use square brackets [] to match any characters in a set.
  • Use \w to match any single alphanumeric character: 0-9 , a-z , A-Z , and _ (underscore).
  • Use \d to match any single digit.
  • Use \s to match any single whitespace character.
Nov 29, 2017

What does $$ mean in Perl? ›

$" - When an array or an array slice is interpolated into a double-quoted string or a similar context such as /.../ , its elements are separated by this value. $$ - The process number of the Perl running this script. $0 - Contains the name of the program being executed.

What does F in Perl mean? ›

-f tests if the provided name references a file that's a plain file. It will return undef (error ENOENT ) if the file doesn't exist, or some other false values if the file exists but it's not plain file (e.g. if it's a directory).

What is the difference between == and EQ in Perl? ›

it says that First, eq is for comparing strings; == is for comparing numbers. "== does a numeric comparison: it converts both arguments to a number and then compares them."

What does while <> mean in Perl? ›

Introduction to Perl while loop statement

The Perl while loop statement executes a code block repeatedly as long as the test condition remains true. The test condition is checked at the beginning of each iteration. The following illustrates the syntax of the Perl while loop statement: while(condition){ # code block }

Why Perl is better than PHP? ›

Perl supports different features such as Unicode characters, Procedural and object-oriented programming, which is extensible and can also be embedded into several other systems, whereas PHP supports several protocols features such as IMAP, POP3, LDAP etc.

Is Perl still worth learning? ›

Yes, Perl is still worth learning because there are a lot of big companies that still use Perl and need Perl developers to work on these codebases. Perl is among the high-paying programming language because there are few talented Perl developers.

Is Perl the best language? ›

Unix-oriented developers still use Perl for system administrator tasks or enhancing their Shell scripts. But as a first programming language, Perl is definitely not your best choice. For example, the well-known programming language Python is much better suited for general-purpose tasks and easier to learn than Perl.

What are the four typical uses of regex? ›

Typical use of Regex:
  • Input Validation.
  • String Parsing.
  • Syntax Highlighting.
  • Data Scraping.
  • Search.
  • String manipulation.
  • Data Mapping.
Nov 28, 2017

What are the two types of regex? ›

In a regular expression it specifies that the previous character set can appear any number of times, including zero. This is a useless regular expression, as you will see shortly. There are also two types of regular expressions: the "Basic" regular expression, and the "extended" regular expression.

What are the best uses for regex? ›

These are some of the common use cases:
  • verify the structure of strings.
  • extract substrings form structured strings.
  • search / replace / rearrange parts of the string.
  • split a string into tokens.
  • Rule-based information Mining systems.
  • Text feature Engineering.
  • Pattern Validation in Forms.
  • Data Extraction, etc.
Feb 23, 2022

How do you match a string with regex? ›

Syntax: How to Match a String to a Regular Expression

Is the character string to match. For example, the regular expression '^Ste(v|ph)en$' matches values starting with Ste followed by either ph or v, and ending with en. Note: The output value is numeric.

Is it hard to learn regular expressions? ›

They are also hard to master: the majority of our studied developers were unaware of critical security risks that can occur when using regexes, and those who knew of the risks did not deal with them in effective manners.

Is regex a useful skill? ›

Regex is known as the IT skill that drastically increases productivity in everything you do on a computer!

What are key words in regex? ›

Keywords and regular expressions are ways to identify types or groups of related URLs for special handling. A keyword is a string of characters (a word, phrase, number, or acronym) that might be found in a URL. When you create a keyword, you associate it with a category.

What is an example of regex pattern? ›

A simple example for a regular expression is a (literal) string. For example, the Hello World regex matches the "Hello World" string. . (dot) is another example for a regular expression. A dot matches any single character; it would match, for example, "a" or "1".

How do you write regex fast? ›

Regex engines match fastest when anchors and literal characters are right there in the main pattern, rather than buried in sub-expressions. Hence the advice to "expose" literal characters whenever you can take them out of an alternation or quantified expression.

What does \s mean in Perl? ›

In addition, Perl defines the following: \w Match a "word" character (alphanumeric plus "_") \W Match a non-word character \s Match a whitespace character \S Match a non-whitespace character \d Match a digit character \D Match a non-digit character.

Is Perl a dead language? ›

While Perl might seem like an outdated scripting language, it still has plenty of relevant uses today.

Is Perl a hard language? ›

Is Perl difficult to learn? No, Perl is easy to start learning -- and easy to keep learning. It looks like most programming languages you're likely to have experience with, so if you've ever written an C program, an awk script, a shell script, or even BASIC program, you're already part way there.

What is Perl vs Python? ›

However, Perl is primarily used for CGI scripts, short codes, and web development. Python is used for web development, desktop development, mobile development, data science, and machine learning. A large part of this has to do with adoption. Both are open-source utilities supported by their communities.

What is the difference between \\ S and \s in regex? ›

The difference is that specifically matches a space, while \s will match any whitespace character ( \r , \n , \t , \f and \v ).

What is the use of $1 in regex? ›

The $ number language element includes the last substring matched by the number capturing group in the replacement string, where number is the index of the capturing group. For example, the replacement pattern $1 indicates that the matched substring is to be replaced by the first captured group.

What does $1 do in regex? ›

The $ number language element includes the last substring matched by the number capturing group in the replacement string, where number is the index of the capturing group. For example, the replacement pattern $1 indicates that the matched substring is to be replaced by the first captured group.

What is the difference between $& and $1 regex? ›

The $& and $1 are not the same. You get the same value because you enclosed the whole pattern in a capturing group. The $& is a backreference to the whole match, while $1 is a backreference to the submatch captured with capturing group 1.

How do you use $1 and $2 in shell script? ›

Process script inputs

Shell scripts have access to some "magic" variables from the environment: $0 - The name of the script. $1 - The first argument sent to the script. $2 - The second argument sent to the script.

What does \s+ do in regex? ›

On the other hand, the \S+ (uppercase S ) matches anything that is NOT matched by \s , i.e., non-whitespace. In regex, the uppercase metacharacter denotes the inverse of the lowercase counterpart, for example, \w for word character and \W for non-word character; \d for digit and \D or non-digit.

What does R '\ 1 mean in regex? ›

The backreference \1 (backslash one) references the first capturing group. \1 matches the exact same text that was matched by the first capturing group. The / before it is a literal character. It is simply the forward slash in the closing HTML tag that we are trying to match.

What is 0 9 ]+ in regex? ›

The [0-9] expression is used to find any character between the brackets. The digits inside the brackets can be any numbers or span of numbers from 0 to 9. Tip: Use the [^0-9] expression to find any character that is NOT a digit.

What is the simplest regex? ›

The simplest regular expression is a single literal character. Except for the special metacharacters *+?()| , characters match themselves. To match a metacharacter, escape it with a backslash: \+ matches a literal plus character.

What is better than regex? ›

String operations will always be faster than regular expression operations. Unless, of course, you write the string operations in an inefficient way. Regular expressions have to be parsed, and code generated to perform the operation using string operations.

Why is regex expensive? ›

regex is expensive – regex is often the most CPU-intensive part of a program. And a non-matching regex can be even more expensive to check than a matching one. regex is greedy – It's extremely easy to match much more than intended, leading to bugs.

What does S |\ S * mean in regex? ›

That regex "\\s*,\\s*" means: \s* any number of whitespace characters. a comma.

What does ++ mean in regex? ›

++ From What is double plus in regular expressions? That's a Possessive Quantifier. It basically means that if the regex engine fails matching later, it will not go back and try to undo the matches it made here.

What is a greedy match in regex? ›

Greedy matching is the default behavior of regular expressions, where the regular expression engine will try to match as much text as possible. In contrast, non-greedy matching, also known as lazy matching, tries to match as little text as possible.


(Crack Concepts)
2. Perl Basics #15: Regular Expressions
3. 2016 - Getting started with modern web development in Perl‎ - Gabor Szabo
(Conference in the Cloud! A Perl and Raku Conf)
4. Perl Scripting: Introduction to Perl | Download Info | Features and First Program
(VLSI Academy)
5. Perl Enough to be dangerous // FULL COURSE 3 HOURS
(Ned Dev)
6. Introduction to Perl - Perl Tutorial for Beginners


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