1. awk

2. awk?
Alfred Aho, Peter Weinberger, Brian Kernighan
Bells Labs 1977

3. You think awk is bad?
Winner of the International Obfuscated C Code (one liner):
main(int c,char**v){return!m(v[1],v[2]);}m(char*s,char*t)
{return*t-42?*s?63==*t|*s==*t&&m(s+1,t+1):!*t:m(s,t+1)||*s&&m(s+1,t);}

4. Awk variants awk - original from AT&T - 1977
nawk - A newer & improved (AT&T)
gawk - The Free Software Foundation

5. Why awk? Excellent filter and report writer.
Processing these rows and columns
Easier to use AWK than most conventional programming languages.
Considered as a pseudo-C interpreter
 understands the same arithmetic operators as C.
Has string manipulation functions, so it can search for particular strings and modify the output.
Has associative arrays, which are incredible useful.

6. Pattern Action Pairs
condition { action } :

7. awk Syntax { [ statement ] ...} variable=expression
print [ expression-list ] [ > expression ]
printf format [ , expression-list ] [ > expression ]
next 
exit

8. awk Syntax - more if ( conditional ) statement [ else statement ]
while ( conditional ) statement
for ( expression ; conditional ; expression ) statement
for ( variable in array ) statement
break
continue

9. BEGIN …. END BEGIN { do something before main body }
condition { action – main body }
END { do this after main body }
e.g., create a file called fields:
#!/bin/awk –f
BEGIN { FS = ":" }
{ print "Name:\t ", $1
print "Year:\t ", $2, "\tMovie: ", $3 }
END { print "Number of records:\t ", NR
print "Number of fields:\t ", NF }
$ chmod 755 fields
$ fields moviedb (or ./fields moviedb if you don’t have $PATTH set)

10. Run as awk or bash script?
#!/bin/sh
awk ‘
BEGIN { print "Using bash -f" }
{print $8, "\t", $3}
END { print " -- completed --" } ‘ Or
#!/bin/awk -f
BEGIN { print "Using awk -f" }

11. Arithmetic Operators Operator Type Meaning + Arithmetic Addition -
Subtraction *
Multiplication /
Division %
Modulo
<space>
String
Concatenation

12. Arithmetic Operators Examples
Expression Result
8+5 13
8-5 3
8*5 40
8/5
1.6
8%5
8 5 85
What’s the output of:
x = 2+1*3 8
Same as: (2+(1*3)) “8”  “58”

13. #0 Put this code in a file called avg
BEGIN { FS = "\t" }
#1 Expect 1st record = number of students
NR == 1 { print "Number of students: ", $1
total=0
next }
#2 Add each record and add to total
{ print $1, "\t", $2
total+=$2
END { print "Average = ", total/NR }
$ cp ~tan/public/scores .
$ avg scores

14. # File: matchregex  Counts number of lines matching regex
BEGIN { total=0 }
/^..*:$/ { # line begins with a ".", followed by any number of chars
# and ends in a colon
print “Found: ", $0 # $0 means whole line
total += 1 }
END { print "\n "
print "#Matches = ", total }
$ chmod 755 match; cp ~tan/public/test .
$ match test

15. Comparing Regex
Operator Meaning ~
Matches !~
Doesn't match

16. # File: matchregex: Counts number of lines where 1st arg matches regex
BEGIN { total=0 }
$1 ~ /^\.[0-9]+.*/ { # line begins with a-m
# followed by any number of char
print "Found:\t", $0 total += 1 }
END { print "#Matches = ", total }
$ chmod 755 matchregex
$ matchregex test

17. # File: matchregex: Counts number of lines where 1st arg matches regex
BEGIN { total=0 }
$1 ~ /^\.[0-9]+.*/ { # line begins with a-m
# followed by any number of char
print "Found:\t", $0 total += 1 }
END { print "#Matches = ", total }
$ chmod 755 matchregex
$ matchregex test

18. Really Weird Syntax !!! Embedding awk in bash
# Bash’s arguments vs. awk’s arguments
# Find an acronym. File: lookup, DBfile: acronym (copy from ~tanjs/public)
#!/bin/sh
awk '$1 == find' find=$1 acronyms # or
awk '$1 ~ find' find=$1 acronyms
Parameters passed to awk are specified after awk script!!
$ chmod 755 lookup
$ lookup GOT acronyms

19. Arithmetic Operators Operator Type Meaning + Arithmetic Addition -
Subtraction *
Multiplication /
Division %
Modulo
<space>
String
Concatenation

20. For loop #!/bin/awk –f BEGIN { sum=0 for (i=1; i <= 10; i++) {
printf "The sum of integers up to : "
printf sum+=i
printf " is "
print sum }
# now end
exit;

21. Associative Arrays #!/bin/awk –f # filename: assArray
BEGIN { FS = "\t" }
{ acro[$1] = $2 }
END { for ( abbrev in acro )
print abbrev, acro[abbrev]
$ assArray acronyms

22. bash & awk combo #!/bin/sh
# arraylookup: look for an abbreviation in a file using associatve array
# Syntax: arraylookup <abbrev> <file>"
assArray $2 | grep $1 }
$ arraylookup GOT acronyms