12.5 Profiling Your awk Programs

You may produce execution traces of your awk programs. This is done by passing the option --profile to gawk. When gawk has finished running, it creates a profile of your program in a file named awkprof.out. Because it is profiling, it also executes up to 45% slower than gawk normally does.

As shown in the following example, the --profile option can be used to change the name of the file where gawk will write the profile:

gawk --profile=myprog.prof -f myprog.awk data1 data2

In the preceding example, gawk places the profile in myprog.prof instead of in awkprof.out.

Here is a sample session showing a simple awk program, its input data, and the results from running gawk with the --profile option. First, the awk program:

BEGIN { print "First BEGIN rule" }

END { print "First END rule" }

/foo/ {
    print "matched /foo/, gosh"
    for (i = 1; i <= 3; i++)
        sing()
}

{
    if (/foo/)
        print "if is true"
    else
        print "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:

foo
bar
baz
foo
junk

Here is the awkprof.out that results from running the gawk profiler on this program and data (this example also illustrates that awk programmers sometimes get up very early in the morning to work):

    # gawk profile, created Mon Sep 29 05:16:21 2014

    # BEGIN rule(s)

    BEGIN {
 1          print "First BEGIN rule"
    }

    BEGIN {
 1          print "Second BEGIN rule"
    }

    # Rule(s)

 5  /foo/ { # 2
 2          print "matched /foo/, gosh"
 6          for (i = 1; i <= 3; i++) {
 6                  sing()
            }
    }

 5  {
 5          if (/foo/) { # 2
 2                  print "if is true"
 3          } else {
 3                  print "else is true"
            }
    }

    # END rule(s)

    END {
 1          print "First END rule"
    }

    END {
 1          print "Second END rule"
    }


    # Functions, listed alphabetically

 6  function sing(dummy)
    {
 6          print "I gotta be me!"
    }

This example illustrates many of the basic features of profiling output. They are as follows:

• The program is printed in the order BEGIN rules, BEGINFILE rules, pattern–action rules, ENDFILE rules, END rules, and functions, listed alphabetically. Multiple BEGIN and END rules retain their separate identities, as do multiple BEGINFILE and ENDFILE rules.
• Pattern–action rules have two counts. The first count, to the left of the rule, shows how many times the rule’s pattern was tested. The second count, to the right of the rule’s opening left brace in a comment, shows how many times the rule’s action was executed. The difference between the two indicates how many times the rule’s pattern evaluated to false.
• Similarly, the count for an if-else statement shows how many times the condition was tested. To the right of the opening left brace for the if’s body is a count showing how many times the condition was true. The count for the else indicates how many times the test failed.
• The count for a loop header (such as for or while) shows how many times the loop test was executed. (Because of this, you can’t just look at the count on the first statement in a rule to determine how many times the rule was executed. If the first statement is a loop, the count is misleading.)
• For user-defined functions, the count next to the function keyword indicates how many times the function was called. The counts next to the statements in the body show how many times those statements were executed.
• The layout uses “K&R” style with TABs. Braces are used everywhere, even when the body of an if, else, or loop is only a single statement.
• Parentheses are used only where needed, as indicated by the structure of the program and the precedence rules. For example, ‘(3 + 5) * 4’ means add three and five, then multiply the total by four. However, ‘3 + 5 * 4’ has no parentheses, and means ‘3 + (5 * 4)’. However, explicit parentheses in the source program are retained.
• Parentheses are used around the arguments to print and printf only when the print or printf statement is followed by a redirection. Similarly, if the target of a redirection isn’t a scalar, it gets parenthesized.
• gawk supplies leading comments in front of the BEGIN and END rules, the BEGINFILE and ENDFILE rules, the pattern–action rules, and the functions.

The profiled version of your program may not look exactly like what you typed when you wrote it. This is because gawk creates the profiled version by “pretty-printing” its internal representation of the program. The advantage to this is that gawk can produce a standard representation. Also, things such as:

/foo/

come out as:

/foo/   {
    print
}

which is correct, but possibly unexpected. (If a program uses both ‘print $0’ and plain ‘print’, that distinction is retained.)

Besides creating profiles when a program has completed, gawk can produce a profile while it is running. This is useful if your awk program goes into an infinite loop and you want to see what has been executed. To use this feature, run gawk with the --profile option in the background:

$ gawk --profile -f myprog &
[1] 13992

The shell prints a job number and process ID number; in this case, 13992. Use the kill command to send the USR1 signal to gawk:

$ kill -USR1 13992

As usual, the profiled version of the program is written to awkprof.out, or to a different file if one was specified with the --profile option.

Along with the regular profile, as shown earlier, the profile file includes a trace of any active functions:

# Function Call Stack:

#   3. baz
#   2. bar
#   1. foo
# -- main --

You may send gawk the USR1 signal as many times as you like. Each time, the profile and function call trace are appended to the output profile file.

If you use the HUP signal instead of the USR1 signal, gawk produces the profile and the function call trace and then exits.

When gawk runs on MS-Windows systems, it uses the INT and QUIT signals for producing the profile, and in the case of the INT signal, gawk exits. This is because these systems don’t support the kill command, so the only signals you can deliver to a program are those generated by the keyboard. The INT signal is generated by the Ctrl-c or Ctrl-BREAK key, while the QUIT signal is generated by the Ctrl-\ key.

Finally, gawk also accepts another option, --pretty-print. When called this way, gawk “pretty-prints” the program into awkprof.out, without any execution counts.

NOTE: Once upon a time, the --pretty-print option would also run your program. This is no longer the case.

There is a significant difference between the output created when profiling, and that created when pretty-printing. Pretty-printed output preserves the original comments that were in the program, although their placement may not correspond exactly to their original locations in the source code. However, no comments should be lost. Also, gawk does the best it can to preserve the distinction between comments at the end of a statement and comments on lines by themselves. This isn’t always perfect, though.

However, as a deliberate design decision, profiling output omits the original program’s comments. This allows you to focus on the execution count data and helps you avoid the temptation to use the profiler for pretty-printing.

Additionally, pretty-printed output does not have the leading indentation that the profiling output does. This makes it easy to pretty-print your code once development is completed, and then use the result as the final version of your program.

Because the internal representation of your program is formatted to recreate an awk program, profiling and pretty-printing automatically disable gawk’s default optimizations.

Profiling and pretty-printing also preserve the original format of numeric constants; if you used an octal or hexadecimal value in your source code, it will appear that way in the output.