1. Chapter 12: gawk Yes it sounds funny

2. In this chapter … Intro Patterns Actions Control Structures Putting it all together

3. gawk? GNU awk awk == Aho, Weinberger and Kernighan Pattern processing language Filters data and generates reports

4. gawk con’t Syntax: gawk [options] [program] [file-list] gawk [options] –f program-file [file-list] Essentially, program is a list of things to pattern match, and then a list of actions to perform Can either be on the command line or in a file

5. gawk program A gawk program contains one or more lines in the format pattern { action } Pattern is used to determine which lines of data to select Action determines what to do with those lines Default pattern is all lines Default action is to print the line Use single quotes around program on CL

6. Patterns Simple numeric or string comparisons = > Regular expressions (see Appendix A) –The ~ operator matches pattern –The !~ operator does not match pattern Combinations using || (OR) and && (AND)

7. Patterns, con’t BEGIN – before any lines are processed END – after all lines are processed pattern1,pattern2 – a range, that starts with pattern 1, and ends with pattern2. After matching pattern2, gawk attempts to match pattern1 again

8. Variables $0 – the current record (line) $1-$n – fields in current record FS – input field separator (default: SPACE / TAB ) NF – number of fields in record NR – current record number RS – input record separator (default: NEWLINE ) OFS – output field separator ORS – output record separator

9. Associative Arrays A variable type similar to an array, but with strings as indexes (instead of integers) Ex –myAssocArray[name] = “Bob” –myAssocArray[hometown] = “Austin” Ex –studentGrades[123-45-6789] = 75 –studentGrades[987-65-4321] = 100

10. Pattern examples $1 ~ /^[A-Z]/ –Matches records where first field starts with a capital letter $3 <= $5 –Matches records where the third field is less than or equal to the fifth field $2 > 5000 && $1 !~ /exempt/ –Matches records where second field is greater than 5000 and first field is not exempt

11. Functions length(str) – returns length of str –Returns length of line if str omitted int(num) – returns integer portion of num tolower(str) – coverts chars to lower case toupper(str) – converts chars to upper case substr(str,pos,len) – returns substring of str starting at pos with length len

12. Actions Default action is print entire record Using print, can print out particular parts (i.e., fields) –Ex. { print $1 } Put literal strings in single quotes By default multiple parameters catenated –Use comma to use OFS Ex. { print $1, $5 }

13. Actions, con’t Separate multiple actions by semicolons Other actions usually involve variables (i.e., incrementors, accumulators) Variables need not be formally initialized By default set to zero or null Standard operators function normally * / % + - = ++ -- += -= *= /= %=

14. Actions, con’t Instead of print you can use printf (c-style) Syntax: –printf “control-string”, arg1, arg2 … argn –control-string contains one or more conversion –%[-][[x].[y]]conv - – left justify x – min field width y – decimal places conv : d – decimal f – floating point s – string Ex: %.2f – floating point with two decimal places

15. Control Structures gawk programs can utilize several control structures Can use if-else, while, for, break and continue All are C-style in syntax (what did the K in gawk stand for?)

16. if … else Syntax: if (condition) { commands } else { commands }

17. while Syntax: while (condition) { commands }

18. for Syntax: for (init; condition; increment) { commands } You can use break and continue for both for and while loops

19. Examples gawk ‘{print}’ cars gawk ‘/chevy/’ cars gawk ‘{print $3, $1}’ cars gawk ‘/chevy/ {print $3, $1} cars gawk ‘$1 ~ /^h/’ cars gawk ‘2000 <= $5 && $5 < 9000’ cars gawk ‘/volvo/, /bmw/’ cars gawk ‘{print $3, $1, “$” $5}’ cars gawk ‘BEGIN {print “Car Info”}’ cars

20. Putting it all together BEGIN{ print " Miles" print "Make Model Year (000) Price" print \ "--------------------------------------------------" } { if ($1 ~ /ply/) $1 = "plymouth" if ($1 ~ /chev/) $1 = "chevrolet" printf "%-10s %-8s %2d %5d $ %8.2f\n",\ $1, $2, $3, $4, $5 }

21. Results gawk -f printf_demo cars Miles Make Model Year (000) Price -------------------------------------------------- plymouth fury 1970 73 $ 2500.00 chevrolet malibu 1999 60 $ 3000.00 ford mustang 1965 45 $ 10000.00 volvo s80 1998 102 $ 9850.00 ford thundbd 2003 15 $ 10500.00 chevrolet malibu 2000 50 $ 3500.00 bmw 325i 1985 115 $ 450.00 honda accord 2001 30 $ 6000.00 ford taurus 2004 10 $ 17000.00 toyota rav4 2002 180 $ 750.00 chevrolet impala 1985 85 $ 1550.00 ford explor 2003 25 $ 9500.00

22. Associative Arrays gawk ‘ {manuf[$1]++} END {for(name in manuf) print name,\ manuf[name]}’ cars | sort bmw 1 chevy 3 ford 4 honda 1 plym 1 toyota 1 volvo 1

23. Standalone Scripts Alternative to issuing gawk –f at command line Just like making a shell script – first line defines what runs script #!/bin/gawk –f Then begin your patterns/actions

24. Advanced gawk getline - allows you to manually pull lines from input –Useful if you need to loop through data Coprocess – direct input or output through a second process, using |& operator Coprocess can be network based using /inet/tcp/0/URL