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Review

Review. Please turn in your homework and practicals sed. Today. Regular Expressions Again! Review grep & sed Again! (The Revenge!) awk. The Guy Who Draws XKCD. I think I have a Bash problem.  What follows is an actual command from my history.

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Review

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  1. Review • Please turn in your homework and practicals • sed

  2. Today • Regular Expressions • Again! • Review • grep & sed • Again! (The Revenge!) • awk

  3. The Guy Who Draws XKCD • I think I have a Bash problem.  What follows is an actual command from my history. • cat /usr/share/dict/words | fgrep -v "'" | perl -ne 'chomp($_); @b=split(//,$_); print join("", sort(@b))." ".$_."\n";' | tee lookup.txt | perl -pe 's/^([^ ]+) .*/\1/g' | awk '{ print length, $0 }' | sort -n | awk '{$1=""; print $0}' | uniq -c | sort -nr | egrep "^[^0-9]+2 " | awk '{ print length, $0 }' | sort -n | awk '{$1=""; print $0}' | perl -pe 's/[ 0-9]//g' | xargs -igrep {} lookup.txt | perl -pe 's/[^ ]+ //g' | tail -n2 • It’s just so hard to bite the bullet, admit that the problem has grown in scope, and move it to its own Perl/Python script.  (P.S. The Guinness Book is wrong.  “Conservationalists” is not a real word.)

  4. Quick Searching • The grep utility is used for matching • Printing to STDOUT – an ‘eyeball’ test or redirection to another file • grep ‘static string’ file >> redirection • grep ‘metacharacters’ file • And grepstarts at the first line, at the beginning of the row, reads across the row, and as soon as it matches its regex, prints • Doesn’t modify, only needs to match once

  5. Replacement • The sed utility is used for ‘substitutions’ • Can either execute once (by default), or across all entries (globally) • Can also print • sed ‘s/from/to/g’ file • sed -n ‘/regex/p’ file

  6. awk is Awkward • Final regex utility is awk • For use when your data is evenly formatted • Teams.txt last two lines • Seattle Mariners • There might be some guys called the Cubs too • No even formatting • First few lines • City Teamname • Even formatting

  7. Example - /etc/passwd • smithj:x:561:561:Joe Smith:/home/smithj:/bin/bash • smith:*:100:100:8A-74(office):/home/smith:/usr/bin/sh • jsmith:x:1001:1000:John Smith:/home/jsmith:/bin/sh • Between each entry is a : • Username:Password:UID:GID:Name:Homedir:Shell • Empty entries are still “bounded” (ie, :: indicates one empty value)

  8. awk Examples • awk-F ‘:’‘{ print $1 }’ /etc/passwd • awk - command • -F ‘:’ - -F sets our ‘delimiter’ to the : character • ‘{ print $1 }’ - action • /etc/passwd - file to use • Prints the first column in the /etc/passwd file • Numbering starts at 1; 0 is the whole file • /etc/passwd is ‘delimited’ by : and empty values still have a : around them

  9. Advanced awk • I will not quiz you on this • The more powerful awk commands are in scripts • #!/bin/bash • awk ‘\ • BEGIN { print “File\tOwner” } \ • { print $0, “\t”, $3} \ • END { print “ – DONE –” } \ • ‘

  10. Case Study • I used awk yesterday • Something close to • awk -F ‘,’ ‘{ print $1\tprint$7}’ example.csv | sort \ • | uniq -c | sort -nr • Counting audit findings so that we could see where to concentrate

  11. Unfortunately • I had to reimage my laptop over the weekend • This wiped out our vm on my system • I have basic commands, but they’re not guaranteed to work • There may be one question on awk on the final

  12. Finally • I have yet to see my son play T-ball • I will be “sick” a week from today (Wednesday, June 4th) so I can see his last game • All late/resubmitted work is due June 9th • Final is Monday, June 16th during normal class time • Just under 50 questions, similar to quizzes

  13. Own Study • Regex’s • Grep, sed and awk

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