bash-tutorial/tutorial/gawk.org

#+TITLE: Using gawk in command-line
#+DATE: 2022-03-15
#+OPTIONS: num:nil toc:nil author:nil
#+PROPERTY: header-args:bash :exports both :session *bsh* :tangle yes
#+PROPERTY: header-args:bash+ :cmdline :results output


* gawk stands for GNU-awk

 ~awk~ is a data driven program that search text in files using a pattern. After finding the pattern
 ~awk~ performs operations on these files.
 ~awk~ is not bash, but since you can use it from a shell, let's talk about ~awk~ in this
  tutorial.

** Syntaxis

   Use the following and apply to files or to standard input ('INPUT')

   #+begin_example bash
     awk PATTERN { ACTION } INPUT
   #+end_example

 ~awk~ can be run directly in the command-line, or you can write scripts and run them.

   #+begin_src bash
     set +H #disabling c-shell-style to avoid treat '!' as special character
   #+end_src

   #+RESULTS:
   | compartido@compartido: | ~/Documentos/GNU/bash/bash-tutorial |
   | compartido@compartido: | ~/Documentos/GNU/bash/bash-tutorial |

   #+begin_src bash
     awk 'BEGIN { print " Don\47t Panic!" }'
   #+end_src

   #+RESULTS:
   | Don't                                 | Panic!                                             |

   To run the program from a file, use the 'f' argument followed by the name of the file.

   #+begin_src bash
      awk -f file.awk
   #+end_src

   #+RESULTS:
   | Dont                                  | Panic!                                             |

 ~awk~ scripts use the following before the code

   #+begin_example bash
   #! /bin/awk -f
   #+end_example

   Then, make the file executable ('chmod +x file.awk')

** Data

   Check in awklib/eg/data

   #+begin_src bash :results output
     awk '/li/ { print $0}' mail-listc
   #+end_src

   #+RESULTS:
   : Amelia   555-5553 amelia.zodiacusque@gmail.comF
   :  Broderick555-0542 broderick.aliquotiens@yahoo.com R
   :  Julie555-6699 julie.perscrutabor@skeeve.com   F
   :  Samuel   555-3430 samuel.lanceolis@shu.eduA
   : compartido@compartido: ~/Documentos/GNU/bash/bash-tutorial

   Printing is the default action. Thus, when printing is omitted, ~awk~
   as action in the code, the output will still be printed.

   #+begin_src bash
     awk 'length($0) > 50' mail-listc
   #+end_src

   #+RESULTS:
   : Anthony  555-3412 anthony.asserturo@hotmail.com   A
   :  Broderick555-0542 broderick.aliquotiens@yahoo.com R
   : compartido@compartido: ~/Documentos/GNU/bash/bash-tutorial

** awk examples

   Compare two text files
   
   $ awk '
NR==FNR {                    # process b.txt  or the first file
    seen[$0]                 # hash words to hash seen
    next                     # next word in b.txt
}                            # process a.txt  or all files after the first
!($0 in seen)' b.txt a.txt   # if word is not hashed to seen, output it


   awk '
   NR==FNR {
   seen[$0]
   next
   }
   !($0 in seen)' diagnostico_es_2022-03-21.org ../reunion/reunion_2022_03_20.org

   git --diff diagnostico_es_2022-03-21.org ../reunion/reunion_2022_03_20.org
   
* References

  - ~awk~ info manual