AWK is an interpreted programming language designed for text processing and report generation. It is typically used for data manipulation, such as searching for items within data, performing arithmetic operations, and restructuring raw data for generating reports in most Unix-like operating systems.
Today, we will explore the AWK philosophy and different types of AWK that exist, starting from its original implementation in 1977 at AT&T’s Laboratories, Inc. We will also look at the various implementation areas of AWK in data science today.
Using AWK programs, one can handle repetitive text-editing problems with very simple and short programs. It is a pattern-action language; it searches for patterns in a given input and, when a match is found, it performs the corresponding action. The pattern can be made of strings, regular expressions, comparison operations on numbers, fields, variables, and so on. It reads the input files and splits each input line of the file into fields automatically.
AWK has most of the well-designed features that every programming language should contain. Its syntax particularly resembles that of the C programming language. It is named after its original three authors:
- Alfred V. Aho
- Peter J. Weinberger
- Brian W. Kernighan
AWK is a very powerful, elegant, and simple that every person dealing with text processing should be familiar with.
This article is an excerpt from a book written by Shiwang Kalkhanda, titled Learning AWK Programming. This book will introduce you to AWK programming language and get you hands-on working with practical implementation of AWK.
Types of AWK
The AWK language was originally implemented as an AWK utility on Unix. Today, most Linux distributions provide GNU implementation of AWK (GAWK), and a symlink for AWK is created from the original GAWK binary. The AWK utility can be categorized into the following three types, depending upon the type of interpreter it uses for executing AWK programs:
- AWK: This is the original AWK interpreter available from AT&T Laboratories. However, it is not used much nowadays and hence it might not be well-maintained. Its limitation is that it splits a line into a maximum 99 fields. It was updated and replaced in the mid-1980s with an enhanced version called New AWK (NAWK).
- NAWK: This is AT&T’s latest development on the AWK interpreter. It is well-maintained by one of the original authors of AWK – Dr. Brian W. Kernighan.
- GAWK: This is the GNU project’s implementation of the AWK programming language. All GNU/ Linux distributions are shipped with GAWK by default and hence it is the most popular version of AWK. GAWK interpreter is fully compatible with AWK and NAWK.
Beyond these, we also have other, less popular, AWK interpreters and translators, mentioned as follows. These variants are useful in operations when you want to translate your AWK program to C, C++, or Perl:
- MAWK: Michael Brennan interpreter for AWK.
- TAWK: Thompson Automation interpreter/compiler/Microsoft Windows DLL for AWK.
- MKSAWK: Mortice Kern Systems interpreter/compiler/for AWK.
- AWKCC: An AWK translator to C (might not be well-maintained).
- AWKC++: Brian Kernighan’s AWK translator to C++ (experimental). It can be downloaded from: https://9p.io/cm/cs/who/bwk/awkc++.ps.
- AWK2C: An AWK translator to C. It uses GNU AWK libraries extensively.
- A2P: An AWK translator to Perl. It comes with Perl.
- AWKA: Yet another AWK translator to C (comes with the library), based on MAWK. It can be downloaded from: http://awka.sourceforge.net/download.html.
When and where to use AWK
AWK is simpler than any other utility for text processing and is available as the default on Unix-like operating systems. However, some people might say Perl is a superior choice for text processing, as AWK is functionally a subset of Perl, but the learning curve for Perl is steeper than that of AWK; AWK is simpler than Perl. AWK programs are smaller and hence quicker to execute. Anybody who knows the Linux command line can start writing AWK programs in no time. Here are a few use cases of AWK:
- Text processing
- Producing formatted text reports/labels
- Performing arithmetic operations on fields of a file
- Performing string operations on different fields of a file
Programs written in AWK are smaller than they would be in other higher-level languages for similar text processing operations. AWK programs are interpreted on a GNU/Linux Terminal and thus avoid the compiling, debugging phase of software development in other languages.
Getting started with installation
This section describes how to set up the AWK environment on your GNU/Linux system, and we’ll also discuss the workflow of AWK. Then, we’ll look at different methods for executing AWK programs.
Installation on Linux
Generally, AWK is installed by default on most GNU/Linux distributions. Using the which command, you can check whether it is installed on your system or not. In case AWK is not installed on your system, you can do so in one of two ways:
- Using the package manager of the corresponding GNU/Linux system
- Compiling from the source code
Let’s take a look at each method in detail in the following sections.
Using the package manager
Different flavors of GNU/Linux distribution have different package-management utilities. If you are using a Debian-based GNU/Linux distribution, such as Ubuntu, Mint, or Debian, then you can install it using the Advance Package Tool (APT) package manager, as follows:
[ shiwang@linux ~ ] $ sudo apt-get update -y [ shiwang@linux ~ ] $ sudo apt-get install gawk -y
Similarly, to install AWK on an RPM-based GNU/Linux distribution, such as Fedora, CentOS, or RHEL, you can use the Yellowdog Updator Modified (YUM) package manager, as follows:
[ root@linux ~ ] # yum update -y [ root@linux ~ ] # yum install gawk -y
For installation of AWK on openSUSE, you can use the zypper (zypper command line) package-management utility, as follows:
[ root@linux ~ ] # zypper update -y [ root@linux ~ ] # zypper install gawk -y
Once the installation is finished, make sure AWK is accessible through the command line. We can check that using the which command, which will return the absolute path of AWK on our system:
[ root@linux ~ ] # which awk /usr/bin/awk
You can also use awk --version to find the AWK version on our system:
[ root@linux ~ ] # awk --version
Compiling from the source code
Like every other open source utility, the GNU AWK source code is freely available for download as part of the GNU project. Previously, you saw how to install AWK using the package manager; now, you will see how to install AWK by compiling from its source code on the GNU/Linux distribution. The following steps are applicable to most of the GNU/Linux software for installation:
- Download the source code from a GNU project ftp site. Here, we will use the wget command line utility to download it, however you are free to choose any other program, such as curl, you feel comfortable with:
[ shiwang@linux ~ ] $ wget http://ftp.gnu.org/gnu/gawk/gawk-4.1.3.tar.xz
- Extract the downloaded source code:
[ shiwang@linux ~ ] $ tar xvf gawk-4.1.3.tar.xz
- Change your working directory and execute the configure file to configure the GAWK as per the working environment of your system:
[ shiwang@linux ~ ] $ cd gawk-4.1.3 && ./configure
- Once the configure command completes its execution successfully, it will generate the make file. Now, compile the source code by executing the make command:
[ shiwang@linux ~ ] $ make
- Type make install to install the programs and any data files and documentation. When installing into a prefix owned by root, it is recommended that the package be configured and built as a regular user, and only the make install phase is executed with root privileges:
[ shiwang@linux ~ ] $ sudo make install
- Upon successful execution of these five steps, you have compiled and installed AWK on your GNU/Linux distribution. You can verify this by executing the which awk command in the Terminal or awk --version:
[ root@linux ~ ] # which awk /usr/bin/awk
Now you have a working AWK/GAWK installation and we are ready to begin AWK programming, but before that, our next section describes the workflow of the AWK interpreter.
Workflow of AWK
Having a basic knowledge of the AWK interpreter workflow will help you to better understand AWK and will result in more efficient AWK program development. Hence, before getting your hands dirty with AWK programming, you need to understand its internals. The AWK workflow can be summarized as shown in the following figure:
Let’s take a look at each operation:
- READ OPERATION: AWK reads a line from the input stream (file, pipe, or stdin) and stores it in memory. It works on text input, which can be a file, the standard input stream, or from a pipe, which it further splits into records and fields:
- Records: An AWK record is a single, continuous data input that AWK works on. Records are bounded by a record separator, whose value is stored in the RS variable. The default value of RS is set to a newline character. So, the lines of input are considered records for the AWK interpreter. Records are read continuously until the end of the input is reached. Figure 1.2 shows how input data is broken into records and then goes further into how it is split into fields:
- Fields: Each record can further be broken down into individual chunks called fields. Like records, fields are bounded. The default field separator is any amount of whitespace, including tab and space characters. So by default, lines of input are further broken down into individual words separated by whitespace. You can refer to the fields of a record by a field number, beginning with 1. The last field in each record can be accessed by its number or with the NF special variable, which contains the number of fields in the current record, as shown in Figure 1.3:
- EXECUTE OPERATION: All AWK commands are applied sequentially on the input (records and fields). By default, AWK executes commands on each record/line. This behavior of AWK can be restricted by the use of patterns.
- REPEAT OPERATION: The process of read and execute is repeated until the end of the file is reached.
The following flowchart depicts the workflow:
We introduced you to the AWK programming language and got ourselves a quick primer to get started with application development.
If you found this post is useful, do check out the book Learning AWK Programming to learn more about the intricacies of AWK programming language for text processing.