Sed & Awk

*sed & awk* describes two text processing programs that are mainstays of the UNIX programmer’s toolbox. *sed* is a stream editor for editing streams of text that might be too large to edit as a single file, or that might be generated on the fly as part of a larger data processing step. The most common operation done with *sed* is substitution, replacing one block of text with another. *awk* is a complete programming language. Unlike many conventional languages, *awk* is data driven — you specify what kind of data you are interested in and the operations to be performed when that data is found. *awk* does many things for you, including automatically opening and closing data files, reading records, breaking the records up into fields, and counting the records. While *awk* provides the features of most conventional programming languages, it also includes some unconventional features, such as extended regular expression matching and associative arrays. *sed & awk* describes both programs in detail and includes a chapter of example *sed* and *awk* scripts. This edition covers features of *sed* and *awk* that are mandated by the POSIX standard. This most notably affects *awk* , where POSIX standardized a new variable, CONVFMT, and new functions, *toupper* () and *tolower* (). The CONVFMT variable specifies the conversion format to use when converting numbers to strings ( *awk* used to use OFMT for this purpose). The *toupper* () and *tolower* () functions each take a (presumably mixed case) string argument and return a new version of the string with all letters translated to the corresponding case. In addition, this edition covers GNU *sed* , newly available since the first edition. It also updates the first edition coverage of Bell Labs *nawk* and GNU *awk* ( *gawk* ), covers *mawk* , an additional freely available implementation of *awk* , and briefly discusses three commercial versions of *awk* , MKS *awk* , Thompson Automation *awk* ( *tawk* ), and Videosoft (VSAwk).