GAWK: Effective AWK Programming

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222 GAWK: Effective AWK ProgrammingARGV[1] = "-"ARGC = 2} else if (ARGC - Optind > 1)do_filenames++# if (IGNORECASE)# pattern = tolower(pattern)}The last two lines are commented out, since they are not needed in gawk. They shouldbe uncommented if you have to use another version of awk.The next set of lines should be uncommented if you are not using gawk. This ruletranslates all the characters in the input line into lowercase if the ‘-i’ option is specified. 1The rule is commented out since it is not necessary with gawk:#{# if (IGNORECASE)# $0 = tolower($0)#}The beginfile function is called by the rule in ‘ftrans.awk’ when each new file isprocessed. In this case, it is very simple; all it does is initialize a variable fcount tozero. fcount tracks how many lines in the current file matched the pattern (naming theparameter junk shows we know that beginfile is called with a parameter, but that we’renot interested in its value):function beginfile(junk){fcount = 0}The endfile function is called after each file has been processed. It affects the outputonly when the user wants a count of the number of lines that matched. no_print is trueonly if the exit status is desired. count_only is true if line counts are desired. egreptherefore only prints line counts if printing and counting are enabled. The output formatmust be adjusted depending upon the number of files to process. Finally, fcount is addedto total, so that we know the total number of lines that matched the pattern:function endfile(file){if (! no_print && count_only)if (do_filenames)print file ":" fcountelseprint fcounttotal += fcount}The following rule does most of the work of matching lines. The variable matches istrue if the line matched the pattern. If the user wants lines that did not match, the sense1 It also introduces a subtle bug; if a match happens, we output the translated line, not the original.
Chapter 13: Practical awk Programs 223of matches is inverted using the ‘!’ operator. fcount is incremented with the value ofmatches, which is either one or zero, depending upon a successful or unsuccessful match.If the line does not match, the next statement just moves on to the next record.A number of additional tests are made, but they are only done if we are not countinglines. First, if the user only wants exit status (no_print is true), then it is enough toknow that one line in this file matched, and we can skip on to the next file with nextfile.Similarly, if we are only printing file names, we can print the file name, and then skip to thenext file with nextfile. Finally, each line is printed, with a leading file name and colon ifnecessary:{}matches = ($0 ~ pattern)if (invert)matches = ! matchesfcount += matches # 1 or 0if (! matches)nextif (! count_only) {if (no_print)nextfile}if (filenames_only) {print FILENAMEnextfile}if (do_filenames)print FILENAME ":" $0elseprintThe END rule takes care of producing the correct exit status. If there are no matches,the exit status is one; otherwise it is zero:END \{if (total == 0)exit 1exit 0}The usage function prints a usage message in case of invalid options, and then exits:function usage( e){
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GAWK: Effective AWK Programming

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