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gawk: Getting Started

 
 1 Getting Started with 'awk'
 ****************************
 
 The basic function of 'awk' is to search files for lines (or other units
 of text) that contain certain patterns.  When a line matches one of the
 patterns, 'awk' performs specified actions on that line.  'awk'
 continues to process input lines in this way until it reaches the end of
 the input files.
 
    Programs in 'awk' are different from programs in most other
 languages, because 'awk' programs are "data driven" (i.e., you describe
 the data you want to work with and then what to do when you find it).
 Most other languages are "procedural"; you have to describe, in great
 detail, every step the program should take.  When working with
 procedural languages, it is usually much harder to clearly describe the
 data your program will process.  For this reason, 'awk' programs are
 often refreshingly easy to read and write.
 
    When you run 'awk', you specify an 'awk' "program" that tells 'awk'
 what to do.  The program consists of a series of "rules" (it may also
 contain "function definitions", an advanced feature that we will ignore
 for now; ⇒User-defined).  Each rule specifies one pattern to
 search for and one action to perform upon finding the pattern.
 
    Syntactically, a rule consists of a "pattern" followed by an
 "action".  The action is enclosed in braces to separate it from the
 pattern.  Newlines usually separate rules.  Therefore, an 'awk' program
 looks like this:
 
      PATTERN { ACTION }
      PATTERN { ACTION }
      ...
 

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