The Apache Tika™ toolkit detects and extracts metadata and text from over a thousand different file types (such as PPT, XLS, and PDF). All of these file types can be parsed through a single interface, making Tika useful for search engine indexing, content analysis, translation, and much more. You can find the latest release on the download page. Please see the Getting Started page for more information on how to start using Tika.
The Text extractor supports a variety of text file formats that all follow a row/column format. It provides a set of delimiters to identify the row and column boundaries and several other parameters to parse the text file and produces a rowset based on the EXTRACT expression’s schema. Updated 7-Zip to 9.13 beta; Updated AutoIt to 3.3.6.1 and replaced deprecated ArrayCreate UDF; Updated InfoZip unzip to 6.0.0; Updated Inno Setup to 5.3.9; Updated innounp to 0.31 (supports Inno Setup 5.3.9) Updated InstallExplorer WCX to 0.9.2; Updated MSI WCX to 1.2.1; Updated PEiD to 0.95; Updated UnRAR to 3.93. Email Extractor Lite 1.6.1: Input Window. Output Option Separator: Group: Addresses Sort Alphabetically Filter Option extract address containing.
If you're interested in contributing to Tika, please see the Contributing page or send an email to the Tika development list.
Tika is a project of the Apache Software Foundation, and was formerly a subproject of Apache Lucene.
Latest News
21 April 2020: Apache Tika Release
Apache Tika 1.24.1 has been released! This release includes enabling gzipping streams for tika-server, security fixes and numerous bug fixes and dependency upgrades. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.24.1.
17 March 2020: Apache Tika Release
Apache Tika 1.24 has been released! This release includes a new artifact to enable starting tika-server as a service via Eric Pugh, improved detection of zip-based formats, more complex PDF processing options, security fixes and numerous bug fixes and dependency upgrades. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.24.
06 December 2019: Apache Tika Release
Apache Tika 1.23 has been released! This release includes a new parser for XLIFF v1.2 files, via Dave Meikle, improved file detection (HEIF/HEIC, FDF and others), and numerous bug fixes and dependency upgrades. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.23.
01 August 2019: Apache Tika Release
Apache Tika 1.22 has been released! This release includes a new parser for HWP files, via SooMyung Lee (soomyung) and JinSup Kim (ddoleye), expanded language coverage in tika-eval and numerous bug fixes and dependency upgrades. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.22.
20 May 2019: Apache Tika Release
Apache Tika 1.21 has been released! This release includes a new parser and detector for CSV files, a new, alpha-level 'auto' mode for running OCR on PDF pages and numerous bug fixes and dependency upgrades. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.21.
22 December 2018: Apache Tika Release
Apache Tika 1.20 has been released! This release includes one critical bug fix: prevent tika-server from responding with a 503 after hitting an OutOfMemory Error (TIKA-2776). Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.20.
9 October 2018: Apache Tika Release
Apache Tika 1.19.1 has been released! This release includes two critical bug fixes: a) fixing the MP3Parser (TIKA-2730) and b) limiting entity expansions in SAX parsing (TIKA-2727). Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.19.1.
18 September 2018: Apache Tika Release
Apache Tika 1.19 has been released! This release requires Java 8. This release includes bug fixes, improved mime detection, security fixes and upgrades to dependencies. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.19.
24 April 2018: Apache Tika Release
Apache Tika 1.18 has been released! This release includes bug fixes (e.g. extraction from grouped shapes in PPT), security fixes and upgrades to dependencies. PLEASE NOTE: The next versions will require Java 8. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.18.
13 December 2017: Apache Tika Release
Apache Tika 1.17 has been released! This release includes new support for automatic image captioning, as well as numerous bug fixes and upgrades to dependencies. PLEASE NOTE: this will be the last version that will support Java 7. The next versions will require Java 8. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.17.
12 July 2017: Apache Tika Release
Apache Tika 1.16 has been released! This release includes integration with USCDataScience's Age Predictor, more warnings for missing optional dependencies, extraction of text from charts and diagrams in ooxml files, and numerous improvements to mime detection. This release removes two dependencies that may have been incompatible with ASL 2.0 -- org.json and jj2000. Please see the CHANGES.txt file for the full list of changes in the release and have a look at the download page for more information on how to obtain Apache Tika 1.16.
30 May 2017: Apache Tika Release
Apache Tika 1.15 has been released! This release includes integration with Google's Tensorflow Object Recognition via the OpenCV API, a new 'tika-eval' module, configurable encoding detectors and several new parsers. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.15.
19 Oct 2016: Apache Tika Release
Apache Tika 1.14 has been released! This release includes integration with Google's Tensorflow Image Recognition via the Inception API, improvements to PDF parsing using OCR, message parsing and MIME detection. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the downlpage page for more information on how to obtain Apache Tika 1.14.
16 May 2016: Apache Tika Release
Apache Tika 1.13 has been released! This release includes some significant changes to the PDF support, including PDFBox 2.0.1, two new NER system support (MIT-NLP Information Extraction and GROBID Quantities), a new tika-langdetect module, and much more. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.13.
6 April 2016: Apache Tika key technology in exposing Panama Papers
As documented on the Forbes article, Apache Tika and Apache Solr were the two linchpin technologies used in the wide exposure of analyzing the Panama papers data files that tracks government corruption and offshore accounts - a global news story.
19 February 2016: Apache Tika Release
Apache Tika 1.12 has been released! This release includes some improvements to Named Entity Recognition (Stanford NER integration and Apache OpenNLP) and additionally efficiency improvements to the GeoTopicParser. There are also bugfixes to Tika REST server in this release. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.12.
25 October 2015: Apache Tika Release
Apache Tika 1.11 has been released! This release includes several improvements that better utilize Java7 support, that help extract more content using the cTAKES clinical extraction system and GROBID journal parser, and improvements to Tesseract extraction. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.11.
01 August 2015: Apache Tika Release
Apache Tika 1.10 has been released! This release includes several improvements including the ability to parse MS Access Files, composite parser creation via Tika Config XML, and many more! Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.10.
23 June 2015: Apache Tika Release
Apache Tika 1.9 has been released. This includes several improvements including parsers that extract additional content e.g., from images using EXIF and FFMPEG, along with improvements to MIME detection using probabilistic means, and updates to the Tika REST server supporting translation and language detection. Please see the CHANGES.txt file for a full list of changes in this release. Have a look at the download page for more information on how to obtain Apache Tika 1.9.
Text Extractor 1 6 0 9 0
20 April 2015: Apache Tika Release
Apache Tika 1.8 has been released! This release includes several bug fixes, tika-batch (a batch processing system for processing large sets of files), and more! Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.8.
15 January 2015: Apache Tika Release
Apache Tika 1.7 has been released! This release includes bug fixes and new features including a new Tesseract OCR Parser; a new GDAL Parser; more supported formats, and overall improvements in Tika stability. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.7.
5 September 2014: Apache Tika Release
Apache Tika 1.6 has been released! This release includes bug fixes and new features including a new Translation API; more supported formats, and overall improvements in Tika stability. Please see the CHANGES.txt file for a full list of changes in this release and have a look at the download page for more information on how to obtain Apache Tika 1.6.
7-9 April 2014: Tika at ApacheCon NA in Denver
ApacheCon NA is in Denver for 2014, and this time we've 5 Tika related talks on the schedule! Do come along to learn more about how Tika works, and how it has been used. See the ApacheCon site for more information and how to attend.
19 Feb 2014: Apache Tika Release
Apache Tika 1.5 has been released! This release includes several important bugfixes and new features. Please see the CHANGES.txt file for a full list of changes in this release, and have a look at the download page for more information on how to obtain Apache Tika 1.5.
1 September 2013: Community News - NSF Proposal Win
Chris Mattmann, Apache Tika PMC member and Adjunct Assistant Professor at the University of Southern California, has won a National Science Foundation proposal for a project to deliver an open source framework for metadata exploration, automatic text mining and information retrieval of polar data using Apache Tika. You can read more here.
Congratulations to Chris and the team at USC!
3 July 2013: Apache Tika Release
Apache Tika 1.4 has been released! This release includes several important bugfixes and new features. Please see the CHANGES.txt file for a full list of changes in this release, and have a look at the download page for more information on how to obtain Apache Tika 1.4.
22 January 2013: Apache Tika Release
Apache Tika 1.3 has been released! This release includes several important bugfixes and new features. Please see the CHANGES.txt file for a full list of changes in this release, and have a look at the download page for more information on how to obtain Apache Tika 1.3.
17 July 2012: Apache Tika Release
Apache Tika 1.2 has been released! This is the first appearance of a few new core sub-modules, including the Tika JAX-RS Network Server, as well as new support for handling XMP metadata. Of course, new file formats have been added and improvements have been made to parsing and detection of existing formats. Please see the CHANGES.txt file for a full list of changes in this release, and have a look at the download page for more information on how to obtain Apache Tika 1.2.
23 March 2012: Apache Tika Release
Apache Tika 1.1 is out the door! We've made a number of improvements to PDF, RTF and MP3 parsing. We've also provided some new features on the command line including the ability to list detectors. Other bug fixes and improvements are listed in the CHANGES.txt file for this release. Have a look at the download page for more information on the release.
7 November 2011: Apache Tika Release
Apache Tika 1.0 has been released, just in time for ApacheCon NA 2011! The 1.0 release of Tika removes all deprecated pre 1.0 API methods, makes several OSGi and Configuration improvements, and improves parsing in RTF, Word and PDF files. Tika no longer ships a retro-translated JDK 1.4 version of the library, so it's time to get on JDK 1.5 or higher to use Tika, so be on the look out. Have a look at the download page for more details.
7-11 November 2011 - Tika at US ApacheCon
ApacheCon NA is coming to Vancouver, British Columbia, at the Westin Bayshore, and Chris Mattmann will be giving a talk on the forthcoming 1.0 release of Tika as part of the Content Technologies track on Thursday November 10th, 2011. The talk will cover the history of Tika, its genesis, its inception as a top-level project, and where it's headed 1.0 and beyond. Come out and support Tika by attending the talk!
30 September 2011: Apache Tika Release
Apache Tika 0.10 has been released. This release includes new parser support for CHM files, bugfixes to RTF parsing, an improved GUI and more. Please see the download page for more details.
16 February 2011: Apache Tika Release
Apache Tika 0.9 has been released. This release includes several important bugfixes and new features. Please see the download page for more details.
12 November 2010: Apache Tika Release
Apache Tika 0.8 has been released. Please see the download page for more details. This is our first release as a TLP. We're excited!
1-5 November 2010 - Tika at US ApacheCon
ApacheCon NA is coming to Atlanta, Georgia, at the Westin Peachtree, and Tika is being repped as part of the Lucene and friends track on Friday, November 5th, 2010. Chris Mattmann will give a talk on how Tika is being used at NASA and in the context of other projects in the Apache ecosystem.
Friday, Nov. 5th, 2010:
Scientific data curation and processing with Apache Tika - Chris Mattmann @ 9:00am
April 2010: Tika Graduates to TLP
Apache Tika was voted into TLP status by a resolution submitted to the Apache Board. We are in the process of updating the site and moving things around. If you notice anything out of place, let us know.
April 2010: Apache Tika Release
Apache Tika 0.7 has been released. Please see the download page for more details.
January 2010: Apache Tika Release
Apache Tika 0.6 has been released. Please see the download page for more details.
November 2009: Apache Tika Release
Apache Tika 0.5 has been released. Please see the download page for more details.
14 August 2009 - Lucene at US ApacheCon
ApacheCon US is once again in the Bay Area and Lucene is coming along for the ride! The Lucene community has planned two full days of talks, plus a meetup and the usual bevy of training. With a well-balanced mix of first time and veteran ApacheCon speakers, the Lucene track at ApacheCon US promises to have something for everyone. Be sure not to miss:
Training:
Lucene Boot Camp - A two day training session, Nov. 2nd & 3rd
Solr Day - A one day training session, Nov. 2nd
Thursday, Nov. 5th:
Introduction to the Lucene Ecosystem - Grant Ingersoll @ 9:00
Lucene Basics and New Features - Michael Busch @ 10:00
Apache Solr: Out of the Box - Chris Hostetter @ 14:00
Introduction to Nutch - Andrzej Bialecki @ 15:00
Lucene and Solr Performance Tuning - Mark Miller @ 16:30
Friday, Nov. 6th:
Implementing an Information Retrieval Framework for an Organizational Repository - Sithu D Sudarsan @ 9:00
Apache Mahout - Going from raw data to Information - Isabel Drost @ 10:00
MIME Magic with Apache Tika - Jukka Zitting @ 11:30
Building Intelligent Search Applications with the Lucene Ecosystem - Ted Dunning @ 14:00
Realtime Search - Jason Rutherglen @ 15:00
July 2009: Apache Tika Release
Apache Tika 0.4 has been released. Please see the download page for more details.
March 2009: Apache Tika Release
Apache Tika 0.3 has been released. Please see the download page for more details.
February 2009: Lucene at ApacheCon Europe 2009 in Amsterdam
Lucene will be extremely well represented at ApacheCon EU 2009 in Amsterdam, Netherlands this March 23-27, 2009:
Lucene Boot Camp - A two day training session, March 23 & 24th
Solr Boot Camp - A one day training session, March 24th
Introducing Apache Mahout - Grant Ingersoll. March 25th @ 10:30
Lucene/Solr Case Studies - Erik Hatcher. March 25th @ 11:30
Advanced Indexing Techniques with Apache Lucene - Michael Busch. March 25th @ 14:00
Apache Solr - A Case Study - Uri Boness. March 26th @ 17:30
Best of breed - httpd, forrest, solr and droids - Thorsten Scherler. March 27th @ 17:30
Apache Droids - an intelligent standalone robot framework - Thorsten Scherler. March 26th @ 15:00
December 2008: Apache Tika Release
Apache Tika 0.2 has been released. Please see the download page for more details.
November 2008: User mailing list created
A new mailing list, tika-user@lucene.apache.org, has been created for discussion about the use of the Tika toolkit. You can subscribe this mailing list by sending a message to tika-user-subscribe@lucene.apache.org.
October 2008: Tika graduates to a Lucene subproject
Tika has graduated form the Incubator to become a subproject of Apache Lucene. The project infrastructure will be migrated from incubator.apache.org to lucene.apache.org.
October 2008: Apache Tika status report
Dave Meikle was just voted in as a new committer.
Paolo Mottadelli will present Tika at ApacheCon US.
Free Email Extractor 1.6 Lite
Tika 0.2 should be released soon.
Usage documentation has been added to the website.
July 2008: Apache Tika status report
Tika community remains relatively small, with just a handful of active members
Work towards Tika 0.2 continues, Chris Mattman has volunteered to be the release manager
April 2008: Apache Tika status report
Niall Pemberton joined the project as a committer and PPMC member
There was a Fast Feather Talk on Tika in ApacheCon EU 2008
We have good contacts especially with Apache POI and PDFBox
We are working towards Tika 0.2
Metadata handling improvements are being discussed
January 2008: Apache Tika status report
No new committers since the last report, activity has been moderate but steady, leading to the 0.1 release.
Tika 0.1 (incubating) has just been released.
Chris Mattmann intends to use that release in Nutch, That's good progress towards Tika's goal of providing data extraction functionality to other projects.
A new Tika logo was created by Google Highly Open Participation student, hasn't been integrated yet.
December 27th, 2007: Tika 0.1-incubating Released!
Tika has made its first official release, titled 0.1-incubating. See the CHANGES.txt file for more information on the list of updates in this initial release. Thanks to all who contributed! You can download the official source tarball here.
Pipe Extractor 1 1 2
October 8th, 2007: Welcome Keith Bennett!
The Tika PPMC has elected Keith Bennett as our new committer. Welcome!
March 22nd, 2007: Apache Tika project started
The Apache Tika project was formally started when the Tika proposal was accepted by the Apache Incubator PMC.
String processing is fairly easy in Stata because of the many built-in string functions. Among these string functions are three functions that are related to regular expressions, regexm for matching, regexr for replacing andregexs for subexpressions. We will show some examples of how to use regular expression to extract and/or replace a portion of a string variable using these three functions. At the bottom of the page is an explanation of all the regular expression operators as well as the functions that work with regular expressions.
Examples
Example 1: A researcher has addresses as a string variable and wants to create a new variable that contains just the zip codes.
Example 2: We have a variable that contains full names in the order of first name and then last name. We want to create a new variable with full name in the order of last name and then first name separated by comma. Macbook screen dump.
Example 2: Dates were entered as a string variable, in some cases the year was entered as a four-digitvalue (which is what Stata generally expects to see), but in other cases it was entered as a two-digitvalue. We want to create a date variable in numeric format based on this string variable. This task can actually easily be handled with regular Stata commands, see our FAQ page “My date variable is a string, how can I turn it into a date variable Stata can recognize?” for information on doing this. We have included this example here for demonstration purposes, not because regular expressions are necessarily the best way to handle this situation.
In these situations, regular expressions can be used to identify cases in whicha string contains a set of values (e.g. a specific word, a number followed by a wordetc.) and extract that set of values from the whole string for use elsewhere.
Example 1: Extracting zip codes from addresses
Let’s start with some fake entries of addresses.
To find the zip code we will look for a five-digit number within an address. The gen command(short for 'generate') below tells Stata to generate a new variable called zip. The rest of the command is a little tricky, the 'if' is evaluated first, if(regexm(address, “[0-9][0-9][0-9][0-9][0-9]”)) searches the variable address for a five digit number, and, if it can find a five digit number in the variable address, the = regexs(0) indicates that Stata should set the value of zip to be equal to that five-digit number. We indicatethat we want a five-digit number by specifying “[0-9]”five times. Unless otherwise indicated using a *, +, or ? mark, one and only one ofthe characters contained in brackets will be matched. This means that stringing five of theseexpressions together will enable us to find a string of exactly five digits. Note that the 0-9 indicates that the expression should match any character 0 through 9 (i.e. 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 are all matches).
Example 1, Variation Number 1
In our simplified example above, none of the addresses have five-digit street numbers. What if there are addresses with five-digit street numbers? Let’s look at another dataset of fake addresses and see what happens when we try to use the same code above.
Apparently, this is not working correctly since the last two rows of the variable zip have picked up the street numbers for these addresses instead of zip codes. In this data set, the zip code appears at the end of the address string. If we assume that this the case for all addresses in the data, the remedy will be really simple. We can specify '[0-9][0-9][0-9][0-9][0-9]$' which would instruct Stata to find a five-digit number at the end of the string.
Example 1, Variation Number 2
Sometimes zip code also include the four-digit extension and the country name may also appear at the end of the address, such as in some of the addresses shown below.
In this type of more realistic situation, the code in the previous examples won’t work correctly since there are extra characters after the zip code to be extracted. Here is how we can do it using a more complicated regular expression.
What we have added in the regular expression is this sub-: '[-]*[0-9]*[ a-zA-Z]*'. There are three components in this regular expression.
[-]* – matching zero or more dashes '-'
[0-9]* – matching zero or more numbers
[ a-zA-Z]* – matching zero or more blank spaces or letters
These additions allow us to match up the cases where there are trailing characters after the zip code and to extract the zip code correctly. Notice that we also used 'regexs(1)' instead of 'regexs(0)' as we did previously, because we are now using subexpressions indicated by the pair of parenthesis in '([0-9][0-9][0-9][0-9][0-9])'. Another strategy that might work better in some cases is the regular expression
In this example, the period (i.e. “.”) matches any charctor, and the asterix alone (“*”) matches any characters. Together, the twoindicate that the number we are looking for should not occur at the very beginning of the string, but may occur anywhere after.
Example 2: Extracting first name and last name and switching their order
We have a variable that contains a person’s full name in the order of first name and then last name. We want to create a new variable for full name in the order of last name and then first name separated by comma. To start, let’s make a sample data set.
Text Extractor 1 6 0 9 Fraction
Now we need to capture the first word and the second word and swap them. Here is the regular expression for this purpose: (([a-zA-Z]+)[ ]*([a-zA-Z]+)).
There are three parts in this regular expression:
([a-zA-Z]+) – subexpression capturing a string consisting of letters, both lower case and upper case. This will be the first name.
[ ]* – matching with space(s). This is the spacing between first name and last name.
([a-zA-Z]+) – subexpression capturing a string consisting of letters. This will be the last name.
This indeed works. Let’s see how regexs works in this case. regex actually identifies a number of sections, based on the whole expression as well as the subexpressions. The following code uses regexs to place each of these components (subexpressions) into its own variableand then displays them.
Example 3: Two- and four- digit values for year.
In this example, we have dates entered as a string variable. Stata can handle this using standard commands (see 'My date variable is a string, how can I turn it into a date variable Stata can recognize?'), we are using this as an example of what you could do with regular expressions. The goal of this process is to produce a stringvariable with the appropriate four digit year for every case, which Stata can then easily convert into a date. To do this we will start by separatingout each element of the date (day, month, and two- or four- digit year) into a separate variable, then we will assign the correct four-digit year to cases where there are currently only two digits, finally, we concatenate the variables to create a single string variable that contains month, day, and four-digit years.
First, input the dates:
Next, we want to identify the day of the month and place it in a variable called day. To do this we instruct Stata to find the day by looking at the beginning of the string (i.e. the date), for one or more values from 0-9. (In other words, look for a numberat the start of the line, since we know the first series of numbers isthe day.) Generate a new variable day, and set it equal to that value.
The line of syntax below finds the month by looking for one or more letters together in the string. Then, generates the variable month and sets it equal to the month identified in the string.
The year is where things get more complex. Note that the values for assigning centuries are based on my knowledge of my “data.” First of all, we extract all the digits for year. We use the '$' operator to indicate that the search is from the end of the string. We then turn the string variable into a numeric variable using Stata’s function 'real'. The next action involves dealing with two digit years starting with '0'. This corresponds to recent years in the twenty first century. To turn these into four-digit years, we concatenate (using the +) the string identified (the two-digit year) with the string '20'. Next we will find the two-digit years 10-99, and concatenate those strings with the string '19'. Finally, we create the variable date2 which is our date containing only four-digit years. (We could also use the three variables, day, month, and year to to create a date variable using the Stata date functions.)
Regular Expressions
Regular expressions are, in general, a way of searching for and in some cases replacing the occurrence of a pattern within a string based on a set of rules. These rules are defined using a set of operators. The following table shows all of the operators Stata accepts, and explains each one. Note that in Stata, regular expressions will always fall within quotation marks.
[ ]
Square brackets indicate that one of the characters inside the brackets should be matched. For example, if I wanted to search for a single letter between f and m, I would type '[f-m]'
a-z
A range specifies that any value within that range is acceptable. This is case sensitive, so a-z is not the same as A-Z, if either case can be counted as a match, include both a-zA-Z. Numeric values are also acceptable as ranges (e.g. 0-9).
.
A period matches any character.
Allows you to match characters that are usually regular expression operators. For example, if you wanted to match a '[' you would type [ instead of just a single [.
*
Match zero or more of the characters in preceding expression. For example if I wanted to match a number made up of one or more digits if there is a number, but still want to indicate a match if the rest of the expression fits, I could specify [0-9]*
+
Match one or more of the characters in the preceding expression. For example if I wanted to match a word containing any combination of letters, I would specify [a-zA-Z]+
?
Match either zero or one of the previous expression.
^
When it appears at the beginning of an expression, a '^' indicates that the following expression should appear at the beginning of the string.
$
When it appears at the end of an expression, a '$' indicates that the preceding expression should appear at the end of the string. For example, if I wanted to match a number that was the last thing to appear at the end of a string, I would specify '[0-9]+$'
|
The logical operator or, indicating that either the expression preceding it or following it qualify as a match.
( )
Creates a subexpression within a larger expression. Useful with the 'or' perator (i.e. | ), and when extracting and replacing values. For example, if I wanted to extract a numeric value which I know follows directly after a word or set of letters, I could use the regular expression “[a-zA-Z]+([0-9]+)' this matches the whole expression, but allows you to select the portion in the parentheses (called a substring). Handling substrings is discussed in greater detail below.
These expressions can be combined to search for a wide variety of strings.
As mentioned above, there are three types of functions that can be preformed with regular expressions in Stata (if you are creative, you can do any number of other things using these functions, but the basic tools are the built in Stata functions). Stata has separate commands for each of the three types of actions regular expressions can perform:
regexm – used to find matching strings, evaluates to one if there is a match, and zero otherwise
regexs – used to return the nth substring within an expression matched by regexm (hence, regexm must always be run before regexs, note that an 'if' is evaluated first even though it appears later on the line of syntax).
regexr – used to replace a matched expression with something else.
Each of these has a slightly different syntax. The line below shows the syntax for regexm, that is, the function that matches your regular expression, where the string may either be a string you type in yourself, a string from a macro, or most commonly, the name of a variable. Regular expression is the regular expression for the string you would like to find, note that it must appear in quotation marks.
For regexs, that is, to recall all or a portion of a string, the syntax is:
Where nNisus writer pro 3 0 48. is the number assigned to the substring you want to extract.The substrings are actually divided when you run regexm. The entire substring isreturned in zero, and each substring is numbered sequentially from 1 to n. For example, regexm(“907-789-3939”, “([0-9]*)-([0-9]*)-([0-9]*)”) returns the following:
Subexpression #
String Returned
0
907-789-3939
1
907
2
789
3
3939
Note that in subexpressions 1, 2, and 3, the dashes are dropped, since they are not included in the parentheses that mark the subexpressions.
You can take another look at how this works using the following syntax, which uses the display command to run the function.
Because they are functions, the regex commands work within other commands (e.g. generate), but cannot be used on their own (i.e. you cannot start a command in Stata with regexm(…)).
Reference
What are regular expressions and how can I use them in Stata?
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