GAWK: Effective AWK Programming

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176 GAWK: Effective AWK ProgrammingThe profiled version of your program may not look exactly like what you typed whenyou wrote it. This is because pgawk creates the profiled version by “pretty printing” itsinternal representation of the program. The advantage to this is that pgawk can producea standard representation. The disadvantage is that all source-code comments are lost, asare the distinctions among multiple BEGIN and END rules. Also, things such as:/foo/come out as:/foo/ {print $0}which is correct, but possibly surprising.Besides creating profiles when a program has completed, pgawk can produce a profilewhile it is running. This is useful if your awk program goes into an infinite loop and youwant to see what has been executed. To use this feature, run pgawk in the background:$ pgawk -f myprog &[1] 13992The shell prints a job number and process ID number; in this case, 13992. Use the killcommand to send the USR1 signal to pgawk:$ kill -USR1 13992As usual, the profiled version of the program is written to ‘awkprof.out’, or to a differentfile if you use the ‘--profile’ option.Along with the regular profile, as shown earlier, the profile includes a trace of any activefunctions:# Function Call Stack:# 3. baz# 2. bar# 1. foo# -- main --You may send pgawk the USR1 signal as many times as you like. Each time, the profileand function call trace are appended to the output profile file.If you use the HUP signal instead of the USR1 signal, pgawk produces the profile and thefunction call trace and then exits.When pgawk runs on MS-DOS or MS-Windows, it uses the INT and QUIT signals forproducing the profile and, in the case of the INT signal, pgawk exits. This is becausethese systems don’t support the kill command, so the only signals you can deliver to aprogram are those generated by the keyboard. The INT signal is generated by the Ctrl-Cor Ctrl-BREAK key, while the QUIT signal is generated by the Ctrl-\ key.
Chapter 11: Running awk and gawk 17711 Running awk and gawkThis chapter covers how to run awk, both POSIX-standard and gawk-specific command-lineoptions, and what awk and gawk do with non-option arguments. It then proceeds to coverhow gawk searches for source files, obsolete options and/or features, and known bugs ingawk. This chapter rounds out the discussion of awk as a program and as a language.While a number of the options and features described here were discussed in passingearlier in the book, this chapter provides the full details.11.1 Invoking awkThere are two ways to run awk—with an explicit program or with one or more programfiles. Here are templates for both of them; items enclosed in [. . .] in these templates areoptional:awk [options] -f progfile [--] file ...awk [options] [--] ’program’ file ...Besides traditional one-letter POSIX-style options, gawk also supports GNU long options.It is possible to invoke awk with an empty program:awk ’’ datafile1 datafile2Doing so makes little sense, though; awk exits silently when given an empty program. If‘--lint’ has been specified on the command line, gawk issues a warning that the programis empty.11.2 Command-Line OptionsOptions begin with a dash and consist of a single character. GNU-style long options consistof two dashes and a keyword. The keyword can be abbreviated, as long as the abbreviationallows the option to be uniquely identified. If the option takes an argument, then thekeyword is either immediately followed by an equals sign (‘=’) and the argument’s value, orthe keyword and the argument’s value are separated by whitespace. If a particular optionwith a value is given more than once, it is the last value that counts.Each long option for gawk has a corresponding POSIX-style option. The long and shortoptions are interchangeable in all contexts. The options and their meanings are as follows:-F fs--field-separator fsSets the FS variable to fs (see Section 3.5 [Specifying How Fields Are Separated],page 43).-f source-file--file source-fileIndicates that the awk program is to be found in source-file instead of in thefirst non-option argument.
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