AWK

    * searches files for lines that contain certain pattern
    * performs operation described in AWK body on line with certain
      pattern.
    * performs operation described in AWK body on choosen line


    * Basic structure

        awk 'program_you_will_write' input-file1 input-file2

        awk 'BEGIN{
            code_in_BEGIN_section
        }

        { code_in_main_body_section }

        END{
            code_in_END_section
        }' input-file1 input-file2

    * AWK Commands

        * In AWK body bash features doesn't work
        * Completely new language in AWK body
            * print
            * if-else
            * for loop
            * ...
        
        * Completely new features we can call on specific line (specific text)
            * NF (number of fields)
            * NR (number of records)
            * RS (records separator)
            * $1,$2,.. (specific fields)
            * ...