GAWK: Effective AWK Programming

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178 GAWK: Effective AWK Programming-v var=val--assign var=valSets the variable var to the value val before execution of the program begins.Such variable values are available inside the BEGIN rule (see Section 11.3 [OtherCommand-Line Arguments], page 182).-mf N-mr NThe ‘-v’ option can only set one variable, but it can be used more than once,setting another variable each time, like this: ‘awk -v foo=1 -v bar=2 ...’.Caution: Using ‘-v’ to set the values of the built-in variables may lead tosurprising results. awk will reset the values of those variables as it needs to,possibly ignoring any predefined value you may have given.Sets various memory limits to the value N. The ‘f’ flag sets the maximumnumber of fields and the ‘r’ flag sets the maximum record size. These two flagsand the ‘-m’ option are from the Bell Laboratories research version of Unix awk.They are provided for compatibility but otherwise ignored by gawk, since gawkhas no predefined limits. (The Bell Laboratories awk no longer needs theseoptions; it continues to accept them to avoid breaking old programs.)-W gawk-optFollowing the POSIX standard, implementation-specific options are supplied asarguments to the ‘-W’ option. These options also have corresponding GNU-stylelong options. Note that the long options may be abbreviated, as long as theabbreviations remain unique. The full list of gawk-specific options is providednext.-- Signals the end of the command-line options. The following arguments are nottreated as options even if they begin with ‘-’. This interpretation of ‘--’ followsthe POSIX argument parsing conventions.This is useful if you have file names that start with ‘-’, or in shell scripts, if youhave file names that will be specified by the user that could start with ‘-’.The previous list described options mandated by the POSIX standard, as well as optionsavailable in the Bell Laboratories version of awk. The following list describes gawk-specificoptions:-O--optimizeEnables some optimizations on the internal representation of the program. Atthe moment this includes just simple constant folding. The gawk maintainerhopes to add more optimizations over time.-W compat-W traditional--compat--traditionalSpecifies compatibility mode, in which the GNU extensions to the awk languageare disabled, so that gawk behaves just like the Bell Laboratories research versionof Unix awk. ‘--traditional’ is the preferred form of this option. See
Chapter 11: Running awk and gawk 179Section A.5 [Extensions in gawk Not in POSIX awk], page 260, which summarizesthe extensions. Also see Section C.1 [Downward Compatibility andDebugging], page 284.-W copyright--copyrightPrint the short version of the General Public License and then exit.-W copyleft--copyleftJust like ‘--copyright’. This option may disappear in a future version of gawk.-W dump-variables[=file]--dump-variables[=file]Prints a sorted list of global variables, their types, and final values to file. Ifno file is provided, gawk prints this list to the file named ‘awkvars.out’ in thecurrent directory.Having a list of all global variables is a good way to look for typographicalerrors in your programs. You would also use this option if you have a largeprogram with a lot of functions, and you want to be sure that your functionsdon’t inadvertently use global variables that you meant to be local. (This is aparticularly easy mistake to make with simple variable names like i, j, etc.)-W exec file--exec fileSimilar to ‘-f’, reads awk program text from file. There are two differences.The first is that this option also terminates option processing; anything else onthe command line is passed on directly to the awk program. The second is thatcommand line variable assignments of the form ‘var=value’ are disallowed.This option is particularly necessary for World Wide Web CGI applicationsthat pass arguments through the URL; using this option prevents a malicious(or other) user from passing in options, assignments, or awk source code (via‘--source’) to the CGI application. This option should be used with ‘#!’ scripts(see Section 1.1.4 [Executable awk Programs], page 13), like so:#! /usr/local/bin/gawk --execawk program here ...-W gen-po--gen-po-W help-W usage--help--usageAnalyzes the source program and generates a GNU gettext Portable Object fileon standard output for all string constants that have been marked for translation.See Chapter 9 [Internationalization with gawk], page 160, for informationabout this option.Prints a “usage” message summarizing the short and long style options thatgawk accepts and then exit.
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GAWK: Effective AWK Programming

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