GAWK: Effective AWK Programming

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218 GAWK: Effective AWK Programming}if (fieldlist == "") {print "cut: needs list for -c or -f" > "/dev/stderr"exit 1}if (by_fields)set_fieldlist()elseset_charlist()set_fieldlist is used to split the field list apart at the commas and into an array.Then, for each element of the array, it looks to see if it is actually a range, and if so, splitsit apart. The range is verified to make sure the first number is smaller than the second.Each number in the list is added to the flist array, which simply lists the fields that willbe printed. Normal field splitting is used. The program lets awk handle the job of doingthe field splitting:function set_fieldlist( n, m, i, j, k, f, g){n = split(fieldlist, f, ",")j = 1 # index in flistfor (i = 1; i = g[2]) {printf("bad field list: %s\n",f[i]) > "/dev/stderr"exit 1}for (k = g[1]; k
Chapter 13: Practical awk Programs 219function set_charlist( field, i, j, f, g, t,filler, last, len){field = 1 # count total fieldsn = split(fieldlist, f, ",")j = 1 # index in flistfor (i = 1; i = g[2]) {printf("bad character list: %s\n",f[i]) > "/dev/stderr"exit 1}len = g[2] - g[1] + 1if (g[1] > 1) # compute length of fillerfiller = g[1] - last - 1elsefiller = 0if (filler)t[field++] = filler}t[field++] = lenlast = g[2]flist[j++] = field - 1} else {if (f[i] > 1)filler = f[i] - last - 1elsefiller = 0if (filler)t[field++] = fillert[field++] = 1last = f[i]flist[j++] = field - 1}# length of field}FIELDWIDTHS = join(t, 1, field - 1)nfields = j - 1Next is the rule that actually processes the data. If the ‘-s’ option is given, thensuppress is true. The first if statement makes sure that the input record does have thefield separator. If cut is processing fields, suppress is true, and the field separator characteris not in the record, then the record is skipped.If the record is valid, then gawk has split the data into fields, either using the characterin FS or using fixed-length fields and FIELDWIDTHS. The loop goes through the list of fields
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GAWK: Effective AWK Programming

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