GAWK: Effective AWK Programming

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174 GAWK: Effective AWK Programming}print "if is true"elseprint "else is true"BEGIN { print "Second BEGIN rule" }END { print "Second END rule" }function sing( dummy){print "I gotta be me!"}Following is the input data:foobarbazfoojunkHere is the ‘awkprof.out’ that results from running pgawk on this program and data(this example also illustrates that awk programmers sometimes have to work late):# gawk profile, created Sun Aug 13 00:00:15 2000# BEGIN block(s)BEGIN {1 print "First BEGIN rule"1 print "Second BEGIN rule"}# Rule(s)5 /foo/ { # 22 print "matched /foo/, gosh"6 for (i = 1; i
Chapter 10: Advanced Features of gawk 175# END block(s)END {1 print "First END rule"1 print "Second END rule"}# Functions, listed alphabetically6 function sing(dummy){6 print "I gotta be me!"}This example illustrates many of the basic rules for profiling output. The rules are asfollows:• The program is printed in the order BEGIN rule, pattern/action rules, END rule andfunctions, listed alphabetically. Multiple BEGIN and END rules are merged together.• Pattern-action rules have two counts. The first count, to the left of the rule, showshow many times the rule’s pattern was tested. The second count, to the right of therule’s opening left brace in a comment, shows how many times the rule’s action wasexecuted. The difference between the two indicates how many times the rule’s patternevaluated to false.• Similarly, the count for an if-else statement shows how many times the condition wastested. To the right of the opening left brace for the if’s body is a count showing howmany times the condition was true. The count for the else indicates how many timesthe test failed.• The count for a loop header (such as for or while) shows how many times the loop testwas executed. (Because of this, you can’t just look at the count on the first statementin a rule to determine how many times the rule was executed. If the first statement isa loop, the count is misleading.)• For user-defined functions, the count next to the function keyword indicates howmany times the function was called. The counts next to the statements in the bodyshow how many times those statements were executed.• The layout uses “K&R” style with TABs. Braces are used everywhere, even when thebody of an if, else, or loop is only a single statement.• Parentheses are used only where needed, as indicated by the structure of the programand the precedence rules. For example, ‘(3 + 5) * 4’ means add three plus five, thenmultiply the total by four. However, ‘3 + 5 * 4’ has no parentheses, and means ‘3 + (5* 4)’.• Parentheses are used around the arguments to print and printf only when the printor printf statement is followed by a redirection. Similarly, if the target of a redirectionisn’t a scalar, it gets parenthesized.• pgawk supplies leading comments in front of the BEGIN and END rules, the pattern/actionrules, and the functions.
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