More details. Bash regular expressions. It's the same thing we did with Said. In this course, learn how to use pattern matching in a Bash script using globs, extended globs, brace expansion, and regular expressions (regex). The element of BASH_REMATCH with index n is the portion of the string matching the nth parenthesized. DevOps Services. 35(1)-release (x86_64-suse-linux-gnu), I would like to negate a test with Regular Expressions. To use extended regular expressions in Cygwin, run egrep or pass the -E flag (note that it's upper-case). ) The plus sign (+) is used to indicate that consecutive delimiters should be treated as one. This is line 4. Basic regular. true if file exists and is a block special file. When it is used, the string to the right of the operator is considered an extended regular expres‐ sion and matched accordingly (as in regex(3)). RegexPlanet - Online Regular Expression (Regex) Testing and Cookbook for: Go, Haskell, Java, JavaScript,. bash will use whatever regex engine is installed on the user's system. 01: Bash scripting various way to determine if a variable is. Note that bash stores the first matched sub-pattern indicated by enclosing parenthesis in the regular expression in the special variable BASH_REMATCH[1] extract. To fully utilize the power of shell scripting, you need to master Regular Expressions. Understanding Regular Expressions Regular Expressions are a feature of UNIX. RegexPlanet - Online Regular Expression (Regex) Testing and Cookbook for: Go, Haskell, Java, JavaScript,. What I understand about "^" is that it searches at the first line and "$" searches at the last line. CRM114 is also useful as a syslog or firewall log filter, to alert you to important events but ignore the ones that aren't meaningful. You can't just write [0-2 55] to match a number between 0 and 255. Introduction [] What is Bash? [Bash is a "Unix shell": a command line interface for interacting with the operating system. Using bash wildcards Common way for rename a mispelled file is to use mv but many dudes will first write the curent name then the new name (ie. W ith the help of BASH shell and IF command, it is possible to find out if a file exists or not on the filesystem. System Center Operations Manager supports two different types of regular expressions. In Python a regular expression search is typically. Bash has quietly made scripting on Unix systems a lot easier with its own regular expressions. Since regular expressions deal with text rather than with numbers, matching a number in a given range takes a little extra care. One can test that a bash variable starts with a string or character in bash efficiently using any one of the following. I just want to make sure I am correct and see how we use these with regular expressions! - Hassen Fatima Apr 20 '15 at 0:35. I have no immediate solution for you without some thought, but the expressions used in the case statement are essentially pathname expressions (such as you use on the command line), not regular expressions:. Regex is a very powerful tool that is available at our disposal & best thing about using regex is that they can be used in almost every computer language. Regular Expression Processing in ABAP Applies to: This document applies to SAP ECC 6. [\()*+?{|^$. This means you're free to copy and share these comics (but not to sell them). The classic example is grep. use regular expression operator =~ when using regex in bash's. The origin of the regular expressions can be traced back to formal language theory or. Bash and regular expressions 1. Learn the fundamentals of Bash regular expressions for the purpose of matching patterns. Regular expressions are constructed analogously to arithmetic expressions by using various operators to combine smaller expressions. We describe an effective way to get all. Regex or Regular Expressions, are use a sequence of characters that define a search pattern. Bash if statements are very useful. The "Environment Variables" Lesson is part of the full, Introduction to Bash, VIM & Regex course featured in this preview video. This guide shows you how to use parameter expansion modifiers to. IP Addresses consist of two kinds. The if-then Statement. Shell case statement is similar to those in Pascal and switch statement in C. com From 2006-2016, Google Code Project Hosting offered a free collaborative development environment for open source projects. The "Environment Variables" Lesson is part of the full, Introduction to Bash, VIM & Regex course featured in this preview video. Advanced Features Local and Global Shell variables. A pattern consists of one or more character literals, operators, or constructs. 25) and it worked fine with all of them. Modelled on the Linux Documentation Project’s HOWTO collection, this collection is an effort to foster documentation that’s more detailed than the Python Library Reference. Users can add, edit, rate, and test regular expressions. This is a job for the test command, that allows to check if file exists and what type is it. To formulate the expression, I used information from the Bash Guide for Beginners which states that: Two regular expressions may be joined by the infix operator "|"; the resulting regular expression matches any string matching either subexpression. me converts your code snippets into pretty-printed HTML format, easily embeddable into blog posts, emails and websites. Bash Shell: Extract Digits From a String [bash] accepted RegEx as a pattern. The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. Now I want to write a regular expression inside the if command that "i | The UNIX and Linux Forums how to use regular expression in Bash Shell Scripting. If you want to search for a pattern that is at one end or the other, you use anchors. Wow this is great resource, thank you for this! It's a mammoth effort. Regular expressions are constructed analogously to arithmetic expressions by using various operators to combine smaller expressions. Bash IF statement is used for conditional branching in the sequential flow of execution of statements. Regex Tester isn't optimized for mobile devices yet. If you use double quotes instead -. Hi, I understand that since Bash 3. In this tutorial, we will implement different types of regular expressions in the Python language. CRM114 is also useful as a syslog or firewall log filter, to alert you to important events but ignore the ones that aren't meaningful. GNU grep is the default on all Linux systems. For example, I would like to conditionally add a path to the PATH variable, if the path is not already there, as in:. A lot of scripting tricks that use grep or sed can now be handled by bash expressions and the bash expressions might just give you scripts that are easier to read and maintain. Based on my Bash experience, I've written Bash 101 Hacks eBook that contains 101 practical examples on both Bash command line and shell scripting. Regular expression tester with syntax highlighting, PHP / PCRE & JS Support, contextual help, cheat sheet, reference, and searchable community patterns. The regular expression pattern for which the Matches(String, Int32) method searches is defined by the call to one of the Regex class constructors. Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. $ -- Match End of the line * -- Match 0 or more occurrence of the previous character. This lesson starts with the basics, and gradually builds to cover more advanced techniques. In this video, learn how this regular expression engine is only available to the if conditional. Subroutine Calls. In this video, learn how if the pattern is expanded in a different order. BASH Scripting aanndd RREEGGEEXX bbaassiiccss FFrreeddLLUUGG HHooww ttoo ddeemmyyssttiiffyy BBAASSHH aanndd RREEGGEEXX Peter Larsen September 27, 2014 Sr. Perl regex tutorial: non-greedy expressions. your expression is gives only 89% correct. 0 take a look at the perldelta page. A regular expression is a string of characters that define the pattern or patterns you are viewing. Bash Tutorial - Learn How to Use dirs pushd and popd Commands by kholidfu. In this section of our Bash Scripting Tutorial you will learn the ways you may use if statements in your Bash scripts to help automate tasks. The term "Regular Expression" is usually abbreviated to regex or regexp. First, we need to. Regular expressions (Regexp)is one of the advanced concept we require to write efficient shell scripts and for effective system administration. The delimiter could be a single character or a string with multiple characters. Net framework uses a traditional NFA regex engine, to learn more about regular expressions look for the book Mastering Regular Expressions by Jeffrey Friedl "Mere enthusiasm is the all in all. Here is a quick summary of the special characters used in the grep tool and their meaning: Text version. I have no immediate solution for you without some thought, but the expressions used in the case statement are essentially pathname expressions (such as you use on the command line), not regular expressions:. It matches any single character except the end of line character. 0, there is a regular expression operator available in bash. Recursion matches the whole regex again at a particular point inside the regex, which makes it possible to match balanced constructs. 0 documentation site The content of this documentation site is built automatically - directly from the documentation created by the Perl developers. The string "abc" is unchanged, because it was not matched by the regular expression. This construct is available from the bash version 2. Regular expressions (regex) are similar to Glob Patterns, but they can only be used for pattern matching, not for filename matching. Bash regular expression replace keyword after analyzing the system lists the list of keywords related and the list of websites with related content, in addition you can see which keywords most interested customers on the this website. Join Grant McWilliams for an in-depth discussion in this video, Use Bash to pull data in seconds, part of Bash Patterns and Regular Expressions. I am looking for someth | The UNIX and Linux Forums. It is possible to make a regular expression look for matches in a case insensitive way but you'll learn about that later on. In this section of our Bash Scripting Tutorial you will learn the ways you may use if statements in your Bash scripts to help automate tasks. In this post, we will see how to use Basic regular expressions to increase the power of grep command. ) The plus sign (+) is used to indicate that consecutive delimiters should be treated as one. Installation. bash$ cat textfile This is line 1, of which there is only one instance. 0_01/jre\ gtint :tL;tH=f %Jn! [email protected]@ Wrote%dof%d if($compAFM){ -ktkeyboardtype =zL" filesystem-list \renewcommand{\theequation}{\#} L;==_1 =JU* L9cHf lp. This tutorial aims to help the reader understanding conditions in bash, and provides a […]. Therefore, you should describe the meaning of the regular expression in the comment of the SQL statement. Otherwise, the else part is attempted instead. PCRE has its own native API as well as a set of wrapper functions that correspond to the POSIX regular expression API. Repetition operators repeat the preceding regular expression a specified number of times. In this course, learn how to use pattern matching in a Bash script using globs, extended globs, brace expansion, and regular expressions (regex). Regular expressions are implemented in the grep command (and its siblings) in bash (found in Cygwin on Windows and Terminal on OSX) and in grep() and its siblings in R. The tables are meant to serve as an accelerated regex course, and they are meant to be read slowly, one line at a time. It is a program which scans a specified file line by line, returning lines that contain a pattern matching a given regular expression. Operator Syntax Description Example eq INTEGER1 -eq INTEGER2 INTEGER1 is equal to INTEGER2 #!/bin/bash read -p "Please enter and confirm number 10 via keyboard : " n. 0, using the =~ operator, just like Perl. Linux bash provides a lot of commands and features for Regular Expressions or regex. 35(1)-release (x86_64-suse-linux-gnu), I would like to negate a test with Regular Expressions. Variables · Functions · Interpolation · Brace expansions · Loops · Conditional execution · Command substitution · One-page guide to Bash scripting. regular expressions are more powerful. We describe an effective way to get all. 35+ Examples of Regex Patterns Using sed and awk in Linux Since there are many engines for regex, we will use the shell regex and see the bash power in working with regex. The element with index 0 is the portion of the string matching the entire regular expression. They describe a pattern to match, a sequence of characters, not words, within a line of text. Local variable can be used in same shell only. Basic regular expressions: This set includes very basic set of regular. The string "abc" is unchanged, because it was not matched by the regular expression. If you use double quotes instead -. En Bash, le regex peut être employé depuis la version 3 après l'opérateur de comparaison =~. 2, the regex match operator =~ either doesn't exist, works differently or has bugs. Extended Regular Expressions. If you want to use perl regex then use perl, otherwise you'll need old fashioned file globbing, which is much more limited than regular expressions, and has different rules. If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters. Linux bash provides a lot of commands and features for Regular Expressions or regex. It's the same thing we did with Said. This construct is available from the bash version 2. Validate password (BASH script) - regex problem If this is your first visit, be sure to check out the FAQ by clicking the link above. Regular expressions are used to search and manipulate the text, based on the patterns. Often case statement lets you express a series of if-then-else statements that check single variable for various conditions or ranges in a more concise way. The character "^" is the starting anchor, and the character "$" is the end anchor. One of the most used feature is to match two or more, multiple string, patterns or regex. It seems that regular expressions [[ str =~ regex ]] do not work in bash. Conditional expression could be binary or unary expression which involves numeric, string or any commands whose return status is zero when success. It's pretty good. ls a+ won't match aaa for example, so if it does support regex, it does barely. Regular expression tester with syntax highlighting, PHP / PCRE & JS Support, contextual help, cheat sheet, reference, and searchable community patterns. We get all the numbers that are found in a string. You can chain three more lookaheads after the first, and the regex engine still won't move. Hi, I understand that since Bash 3. The source code examples in this article show how to use Regular Expressions to validate different inputs. To implement regular expressions, the Python's re package can be used. Therefore, when issued on the command line, they are separated by a semi-colon. The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. Ksh Regular Expressions. mv old_file. Bash regex test keyword after analyzing the system lists the list of keywords related and the list of websites with related content, in addition you can see which keywords most interested customers on the this website. Validate password (BASH script) - regex problem If this is your first visit, be sure to check out the FAQ by clicking the link above. How to Valid IPv6 Addresses using BASH and Regex ? March 13, 2016 No Comments BASH Shell, hacker rank, online judge, regex. Bash Tutorial - Learn How to Use dirs pushd and popd Commands by kholidfu. Double square brackets provide several important enhancement such as: The =~ operator for regular expression matching; The == operator is available for pattern matching. The site also has a page about Perl regex, but this one is only about one liners. (2) to find a substring which matches certain pattern, from a whole text. Regular expressions are a system for describing compl This tutorial will cover how to use regular expressions to explore the power of the 'grep' command. Variables · Functions · Interpolation · Brace expansions · Loops · Conditional execution · Command substitution · One-page guide to Bash scripting. The following examples will pass the regular expression, but are all invalid dates: 20180231, 20190229, 20190431. Find and replace items using regular expressions. Advanced Features Local and Global Shell variables. See post #7 ---- First, doesn't bash already include a bash: checking if a variable is a number (need regular expression help). You can use it for manipulating and expanding variables on demands without using external commands such as perl, python, sed or awk. Any command-line expert knows the power of regular expressions. Split to get numbers from a string. It is this core syntax that Stata implements in its regular-expression functions. One of the most common operations when working with strings in Bash is to determine whether or not a string contains another string. Using BASH =~ regex to match multiple strings. NET Regular Expressions. Solutions Architect, Red Hat 2. Bash Tutorial - Learn How to Use dirs pushd and popd Commands by kholidfu. Variables · Functions · Interpolation · Brace expansions · Loops · Conditional execution · Command substitution · One-page guide to Bash scripting. This tutorial aims to help the reader understanding conditions in bash, and provides a […]. DevOps Services. Written by Zeph Grunschlag. /R Uses search strings as regular expressions. pdf), Text File (. A conditional expression (also know as “evaluating expressions”) can be used by [[compound command and the test ([) builtin commands to test file attributes and perform string and arithmetic comparisons. Certain commands and utilities commonly used in scripts, such as grep, expr, sed and awk interpret and use REs. The Python module re provides full support for Perl-like regular expressions in Python. It is a free online regular expression builder that will show you the results of your regular expression in real-time. The idea of the regular expression. Any command-line expert knows the power of regular expressions. If you're still leaning on grep and sed commands to get your scripts. It's too bad the. Tagged as: Tags Bash, bash case in esac, bash if. Using GNU bash (version 4. Regular expressions are implemented in the grep command (and its siblings) in bash (found in Cygwin on Windows and Terminal on OSX) and in grep() and its siblings in R. Check if a string matches a regex in Bash script. Python HOWTOs are documents that cover a single, specific topic, and attempt to cover it fairly completely. +?)\1+$ regular expression can tell you if a number is not prime? In this blog post you'll learn how and why it works. They allow us to decide whether or not to run a piece of code. A lot of scripting tricks that use grep or sed can now be handled by bash expressions and the bash expressions might just give you scripts that are easier to read and maintain. Sed Awk Grep Bash. Later bash (starting from version 3. This is the only instance of line 2. com Tel: (707) 827-7019 or 1-800-889-8969 Mon-Fri, 1am–5pm Pacific Time, excluding US holidays. your expression is gives only 89% correct. Validate password (BASH script) - regex problem If this is your first visit, be sure to check out the FAQ by clicking the link above. Linux bash provides a lot of commands and features for Regular Expressions or regex. – barlop Mar 1 '11 at 13:51. We highly recommend that you learn and use this type of regular expression syntax, as it is far more powerful (and in some cases even simpler) than the regular expression types covered in this power tip. It is very simple to study regular expression syntax, and the few abstract concepts can be understood easily too. ShellCheck is an open source static anaylsis tool that automatically finds bugs in your shell scripts. Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. In this video, learn how this regular expression engine is only available to the if conditional. Ksh has it's own regular expressions. Regular Expressions in SciTE Purpose. Learn to use regex in Linux for bash scripting. Here's what you'd learn in this lesson: James introduces environment variables, what are variables defined by the shell and shell scripts. If you're using Bash earlier than version 3. The origin of the regular expressions can be traced back to formal language theory or. It is this core syntax that Stata implements in its regular-expression functions. Throughout this course, Grant McWilliams covers the differences between basic and extended regexes and delves into using extended regexes in bash conditional statements, grep, sed, and AWK. Regular expression metacharacters. use regular expression operator =~ when using regex in bash's. The re module raises the exception re. Because you. It does indeed break when PWD contains regex operators. Since you already know perl, I'd suggest writing a small script like the one below, that will be usefull in may places. Regex is a very powerful tool that is available at our disposal & best thing about using regex is that they can be used in almost every computer language. Note! I use Bourne shell or derivatives thereof, like BASH. Regular expressions are not a tool in and of themselves, but are included as part of a larger utility. The syntax of regular expressions in Perl is very similar to what you will find within other regular expression. Bash Shell Script to check if a string has only alphabets and digits. In this course, learn how to use pattern matching in a Bash script using globs, extended globs, brace expansion, and regular expressions (regex). They are also used on the Bash command-line, but as always, there are slight differences in the syntax. variable assignment Initializing. Certain commands and utilities commonly used in scripts, such as grep, expr, sed and awk interpret and use REs. The "Environment Variables" Lesson is part of the full, Introduction to Bash, VIM & Regex course featured in this preview video. Otherwise, the else part is attempted instead. This is line 3, another line. This page gives a basic introduction to regular expressions themselves sufficient for our Python exercises and shows how regular expressions work in Python. Just copy the source code to the left pane, select the language and the color scheme, and click "Highlight!". Sed Awk Grep Bash. Active 4 years, bash regex sed. Regular expressions do not interpret any meaning from the search pattern. Regular expressions (Regexp)is one of the advanced concept we require to write efficient shell scripts and for effective system administration. At a high level, regular expressions are a way of defining patterns of text to operate on. If you’ve been thinking about mastering Bash, do yourself a favor and read this book, which will help you take control of your Bash command line and shell scripting. com Tel: (707) 827-7019 or 1-800-889-8969 Mon-Fri, 1am–5pm Pacific Time, excluding US holidays. 35+ Examples of Regex Patterns Using sed and awk in Linux Since there are many engines for regex, we will use the shell regex and see the bash power in working with regex. Certain commands and utilities commonly used in scripts, such as grep, expr, sed and awk, interpret and use REs. txt) or read online for free. Note that bash stores the first matched sub-pattern indicated by enclosing parenthesis in the regular expression in the special variable BASH_REMATCH[1] extract. To fully utilize the power of shell scripting, you need to master Regular Expressions. 35(1)-release (x86_64-suse-linux-gnu), I would like to negate a test with Regular Expressions. You may have to register before you can post: click the register link above to proceed. Since you already know perl, I'd suggest writing a small script like the one below, that will be usefull in may places. How to Valid IPv6 Addresses using BASH and Regex ? March 13, 2016 No Comments BASH Shell, hacker rank, online judge, regex. If you bash script then it is a good idea to make sure it does not matter where you put the script and what is your current working directory when you run it. Your question is confusing: you can either have an exact match (stings are identical) or you can have a regex match (string matches the template in a regular expression). These patterns are used with the exec and test methods of RegExp, and with the match, matchAll, replace, search, and split methods of String. UPDATE: I designed a bunch of regular expressions which seems to work extraordinarily well. What Is grep? Grep is a command-line tool that allows you to find a string in a file or stream. For more information about the elements that can form a regular expression pattern, see Regular Expression Language - Quick Reference. You can think of regular expressions as wildcards on steroids. It is this core syntax that Stata implements in its regular-expression functions. In some cases, we might know that there are specific characters that we don't want to match too, for example, we might only want to match phone numbers that are not from the area code 650. Read the repetion example carefully, and pay careful attention to the fact that the "*" in grep patterns denotes repetition. i'm not sure to what extent if at all. hello I want to do a pattern match for string in the if statement, but I am not sure how to use regex inside the if statement. There has been 6 replies and 1 user thanks in this discussion and the last reply was by skrtxao. A regular expression is a pattern that describes a set of strings. All they do is look for exact matches to specifically what the pattern describes. Regular expressions are constructed analogously to arithmetic expressions by using various operators to combine smaller expressions. Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. The source code examples in this article show how to use Regular Expressions to validate different inputs. txt) or read online for free. bash$ cat textfile This is line 1, of which there is only one instance. You don't need to know about regular expressions - just use the template shown here. Regular Expressons. Bash Shell: Extract Digits From a String [bash] accepted RegEx as a pattern. Within ‘[’ and ‘]’, an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c. Matching Numeric Ranges with a Regular Expression. In the regular expression processing described in IEEE Std 1003. How do I check if variable begins with # in bash shell scripting running on a Linux or Unix-like operating systems? Introduction – In bash, we can check if a string begins with some value using regex comparison operator =~. One of the most used feature is to match two or more, multiple string, patterns or regex. Use Bash to pull data in seconds - [Instructor] Sed is a stream editor, meaning it will edit text as the text is piped through it. In a script, the different parts of the if statement are usually well-separated. This is line 4. Let's take a deep dive in the Unix shell's if statement. The $ character is used for parameter expansion, arithmetic expansion and command substitution. The word character class matches letters, digits, and the character ‘_’. The origin of the regular expressions can be traced back to formal language theory or. It is possible to make a regular expression look for matches in a case insensitive way but you'll learn about that later on. In this course, learn how to use pattern matching in a Bash script using globs, extended globs, brace expansion, and regular expressions (regex). Certain commands and utilities commonly used in scripts, such as grep, expr, sed and awk interpret and use REs. They allow us to decide whether or not to run a piece of code. how do I ignore \s in: echo \sbananas? This prints out "sbananas", not "bananas". The author of RegexBuddy calls this catastrophic backtracking, and he has a page describing how to avoid catastrophic backtracking in your regular expressions: The solution is simple. [a-z] looks a bit regex like and bash seems to accept that. Comparison operators are operators that compare values and return true or false. Just copy the source code to the left pane, select the language and the color scheme, and click "Highlight!". You can also submit an answer or search documents about how do you transfer songs from our ipod to my son s new mp3 player. This chapter covers standard regular expressions with suitable examples. pdf), Text File (. It returns an array of information or null if no match are found. Write a bash script so that it receives arguments that are specified when the script is called from the command line. (3) to do complex replacement in a text. In a script, the different parts of the if statement are usually well-separated. This is a document that covers some issues regarding shell script programming. 25(1)-release I've tried using the script on RHEL 6. In JavaScript, regular expressions are also objects. Regular expressions (also known as pattern matching) occur not only in Vim and Grep. Extended Regular Expressions were added to Bash version 3 and made more robust in later versions. subname) with the regular expression:. System Center Operations Manager supports two different types of regular expressions. Regular expressions are great at matching. Many people think that RegExp is alien to Bash/KSH Scripting and depends on GREP or SED to use regexp extensively. The string "abc" is unchanged, because it was not matched by the regular expression. Global variables or environment variables are available in all shells. A lot of scripting tricks that use grep or sed can now be handled by bash expressions and the bash expressions might just give you scripts that are easier to read and maintain. Written by Zeph Grunschlag. Makes a copy of the target sequence (the subject) with all matches of the regular expression rgx (the pattern) replaced by fmt (the replacement). Comparing Strings. The regular expression is a sequence of characters that define a search pattern. Skills: C Programming, Shell Script See more: \ will provide details later\ , parsing numbers text using regex, convert text excel using monarch, using sed, bash extract substring regex, awk search for string in file, awk, awk examples, awk filter regex, grep regex, sed regex, combine text files using excel macro,. Since you already know perl, I'd suggest writing a small script like the one below, that will be usefull in may places. Bash IF statement is used for conditional branching in the sequential flow of execution of statements. Shellhacks. But from Version 3 of Bash we can use a regular expression without using grep or sed. Bash Tutorial - Learn How to Use dirs pushd and popd Commands by kholidfu. The regular expressions have more meta-characters to construct flexible patterns. As we all know we can use conditional statements in BASH. It is possible to make a regular expression look for matches in a case insensitive way but you'll learn about that later on. This is the only instance of line 2. # Awk numbers first character of string as '1'. Regular Expressions. A character class matches any character belonging to that class. Within '[' and ']', an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c. One can test that a bash variable starts with a string or character in bash efficiently using any one of the following. Many people think that RegExp is alien to Bash/KSH Scripting and depends on GREP or SED to use regexp extensively. The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.