@@ -605,6 +605,26 @@ each line if it matches some pattern. If it does, the action will be executed.
605605 END {...}
606606#+END_SRC
607607
608+ *Note*: The ~BEGIN~ and ~END~ are known as *startup* and *cleanup* actions,
609+ respectively. Each of them are executed only once. The ~BEGIN~ content is
610+ executed before the input record is read in, while the ~END~ content is
611+ executed after the input record is done being read in.
612+ 613+ #+BEGIN_SRC sh
614+ # List student directories
615+ ls -l /home/courses/BMI565/students
616+ #+END_SRC
617+ 618+ #+RESULTS:
619+ 620+ #+BEGIN_SRC sh
621+ # Example pipe list of directories and count them
622+ ls -l /home/courses/BMI565/students | awk '
623+ BEGIN { print "Analyzing student directory..." }
624+ /^drw/ { ++n }
625+ END { print "There are", n, "number of directories." }'
626+ #+END_SRC
627+ 608628*** Built-in variables
609629
610630There are some built-in variables that can be used to make using ~awk~ more
@@ -621,7 +641,7 @@ columns/fields in the file, which may be useful in manipulating the file.
621641| NF | Number of fields/columns | ~awk '{print NR,"->",NF;}'~ |
622642| FILENAME | Name of current file | ~awk '{print FILENAME}'~ |
623643| FNR | Number of records rel. to current | ~awk '{print FILENAME, FNR;}'~ |
624- | 0ドル | The entire line | ~awk '{print 0ドル;}` ~ |
644+ | 0ドル | The entire line | ~awk '{print 0ドル;}' ~ |
625645| $n | The nth field number | ~awk '{print 1ドル;}'~ |
626646
627647*** Examples
@@ -630,13 +650,25 @@ Now that we have the general syntax, let's try out some ~awk~ commands.
630650
631651#+BEGIN_SRC sh
632652 # Reminder of what the -l flag does
633- ls -l
653+ ls -l /home/courses/BMI565/students
654+ #+END_SRC
655+ 656+ #+BEGIN_SRC sh
657+ # Examples of awk and potential extracting and manipulating information
658+ ls -l /home/courses/BMI565/students | awk '{ print 6,ドル9ドル }'
659+ #+END_SRC
660+ 661+ #+BEGIN_SRC sh
662+ # Do some manipulation of entries
663+ ls -l /home/courses/BMI565/students | awk '{ print 7ドル * 2 }'
634664#+END_SRC
635665
636666#+BEGIN_SRC sh
637- # Examples of awk and potential actions
638- ls -l | awk '{ print 6ドル " " 9ドル }'
639- ls -l | awk '{ print 7ドル * 2 }'
667+ # More advanced example
668+ ls -l /home/courses/BMI565/students | awk '
669+ BEGIN { print "Checking dates of user directories..." }
670+ 8ドル < 15 { print $NF, "was edited earlier in that month" }
671+ END { print "There were a total of", NR, "users." }'
640672#+END_SRC
641673
642674*** Resources and more
@@ -647,6 +679,7 @@ Now that we have the general syntax, let's try out some ~awk~ commands.
647679- [[http://www.grymoire.com/Unix/Awk.html][Awk (Grymoire)]]
648680- [[https://ss64.com/bash/awk.html][awk or gawk (GNU awk)]]
649681- [[https://github.com/learnbyexample/Command-line-text-processing/blob/master/gnu_awk.md][Learn by Example awk]]
682+ - [[https://www.gnu.org/software/gawk/manual/html_node/Using-BEGIN_002fEND.html][Startup and Cleanup Actions with BEGIN and END]]
650683
651684** sed - edit streams of text
652685
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