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Lecture 7.2

Lecture 7.2. awk. History of AWK. The name AWK Initials of designers: Alfred V. A lo , Peter J. W einberger, and Brian W. K ernighan. Appear 1977, stable release 1985 In BSD, OS X: bawk or nawk . GNU/Linux : gawk The basic function of AWK:

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Lecture 7.2

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  1. Lecture 7.2 awk

  2. History of AWK • The name AWK • Initials of designers: Alfred V. Alo, Peter J. Weinberger, and Brian W. Kernighan. • Appear 1977, stable release 1985 • In BSD, OS X: bawk or nawk. • GNU/Linux : gawk • The basic function of AWK: • Search files for lines that contains certain patterns

  3. Basic command • pattern {action} Use single quote, to avoid shell interpret the pattern The whole line • awk ‘/foo/{print $0}’ file pattern, can use R.E pattern is optional print the whole line that matches pattern

  4. The Basics of AWK • A line is called a record • text separated by delimiter is called field • $0, $1, ... etc • $0 : the whole line • $1 : the first field in a line • NR : Number of record • also the line number • NF : number of fields in a line

  5. Demos % cat employees Tom Jones 4424 5/12/66 543354 Mary Adams 5346 11/4/63 28765 Sally Chang 1654 7/22/54 650000 Billy Black 1683 9/23/44 336500 • %awk ‘{print NR, $1, NF}’ employees • 1 Tom 5 • 2 Mary 5 • 3 Sally 5 • 4 Billy 5 print line number, employee first name, and number of fields

  6. The Basics of AWK cont. • FS : field separator • default is space and/or tabs (strip the leading blanks) • change by -F (e.g. -F:, -F’[ :\t]’ ) • OFS : output field separator • default is space • change by ‘{OFS=DELIMITER};’ • %awk ‘{OFS=“-----”} ;{print $1, $2}’ employees Tom----Jones Mary----Adams Sally----Chang Billy----Black

  7. Demos %cat newlist.txt Tom Jones:4424:5/12/66:543354 Mary Adams:5346:11/4/63:28765 Sally Chang:1654:7/22/54:650000 Billy Black:1683:9/23/44:336500 %awk-F: '{print $1}' newlist.txt Tom Jones Mary Adams Sally Chang Billy Black use ‘:’ as the delimiter, instead of space awk –F: ‘{print $1}’ newlist %awk-F'[: ]' '{print $1}' newlist.txt Tom Mary Sally Billy Use ‘:’ and ‘ ‘ as delimiter

  8. Awk patterns and actions • awk ‘$3<4000’ employees • print lines where $3 is less than 4000 • awk ‘/Tom/{print “Hello, “ $1}’ employees • find the line contains Tom, then print “Hello Tom” • awk ‘$1 !~ /ly$/{ print $1}’ employees • print the names that dose not end with ly

  9. Awk in script #file: awk_first /Tom/{print “Tom‘s birthday is ” $3} /Mary/{print NR, $0} #print line number /^Sally/{print "Hi, Sally. " $1 " has salary of $" $4 "."} % awk –F: -f awk_first newlist.txt

  10. AWK comparison expression • Conditional expression • condition? exp1 : exp2 • Logical Operation • &&, ||, !

  11. Condition expression example % awk ‘{max=($1>$2)? $1 : $2; print max}’ filename %cat needmax.txt 1 2 3 5 6 3 7 2 % awk '{max=($1>$2)? $1 :$2; print max}' needmax.txt 2 5 6 7 awk '{ max=0; if ($1 > $2 ) $max = $1 ; else $max = $2; print $max;}' needmax.txt

  12. datafile

  13. More comparison examples • awk ‘$7==5{print $7+5}’ datafile • print lines where the 7th field is 5 • awk ‘$2==“CT” { print $1, $2}’ datafile • print the 1st and 2nd field of lines that the 2nd field is CT • awk‘!($2==“NW”) || $1 ~ /south/{ print $0}’ datafile • awk '$8 > 10 && $8 < 17' datafile

  14. Math operators • awk '/southern/{print $5 + 10.56}' datafile • awk '/southern/{print $8 - 10}' datafile • awk '/southern/{print $8 / 2}' datafile • awk '/southern/{print $8 * 2}' datafile • awk '/northeast/ {print $8 % 3}' datafile

  15. Assignment Operator assignment operators: =, +=, -=, *=, /=, %=, ^= increment and decrement: ++, -- • awk'$3 == "Chris"{ $3 = "Christian"; print}' datafile • if a line’s 3rd field is “Chris”, change it to Christian and print out the line • awk ‘/Derek/{$8+=12; print $8}’ datafile • awk ‘{$7^=2; print $7}’ datafile • square the 7th field and print out the 7th field • awk ‘{x=1; y=x++; print x, y}’ datafile

  16. BEGIN Patterns • BEGIN pattern is followed by an action block that is executed before AWK processes any lines from the input file. • can run an awk command without file • %awk ‘BEGIN{ print “Hello”;}’ • % awk‘BEGIN{FS=“:”; OSF=“—”; ORS=“\n\n”}{print $1 $2 $3}’ newlist.txt Tom Jones---4424---5/12/66 Mary Adams---5346---11/4/63 Sally Chang---1654---7/22/54 Billy Black---1683---9/23/44

  17. END Patterns • END patterns executes the commands after processing a file • %awk ‘END{ print “The number of records is “ NR}’ employees • awk'/Mary/{count++}END{print "Mary was found " count " times."}' employees The number of records is 4 Mary was found 1 times.

  18. Redirections and Pipes • > :save to file • >> :append to file • awk '$7 >=5 {print $1, $2, $7> “out.txt" }‘ datafile • instead of print to screen, save to ‘out.txt’ file %cat out.txt western WE 5 eastern EA 5 north NO 5 central CT 5

  19. Pipe %awk'/ly/{print $1, $2}' employees Sally Chang Billy Black %awk'/ly/{print $1, $2 |"sort"}' employees Billy Black Sally Chang %awk '/ly/{print $1, $2 |"sort | head –n1"}' employees Billy Black Sally Chang # you can chain as many as you want

  20. There are much more to explore • conditional statement • loop • arrays • user-defined functions. Suggest Read Chapter 6 of the book

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