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Recipe 8.2 Counting Lines (or Paragraphs or Records) in a File8.2.1 ProblemYou need to compute the number of lines in a file. 8.2.2 SolutionMany systems have a wc program to count lines in a file: $count = `wc -l < $file`; die "wc failed: $?" if $?; chomp($count); You could also open the file and read line-by-line until the end, counting lines as you go: open(FILE, "<", $file) or die "can't open $file: $!"; $count++ while <FILE>; # $count now holds the number of lines read Here's the fastest solution, assuming your line terminator really is "\n": $count += tr/\n/\n/ while sysread(FILE, $_, 2 ** 20); 8.2.3 DiscussionAlthough you can use -s $file to determine the file size in bytes, you generally cannot use it to derive a line count. See the Introduction in Chapter 9 for more on -s. If you can't or don't want to call another program to do your dirty work, you can emulate wc by opening up and reading the file yourself: open(FILE, "<", $file) or die "can't open $file: $!"; $count++ while <FILE>; # $count now holds the number of lines read Another way of writing this is: open(FILE, "<", $file) or die "can't open $file: $!"; for ($count=0; <FILE>; $count++) { } If you're not reading from any other files, you don't need the $count variable in this case. The special variable $. holds the number of lines read since a filehandle was last explicitly closed: 1 while <FILE>; $count = $.; This reads in all records in the file, then discards them. To count paragraphs, set the global input record separator variable $/ to the empty string ("") before reading to make the input operator (<FH>) read a paragraph at a time. $/ = ""; # enable paragraph mode for all reads open(FILE, "<", $file) or die "can't open $file: $!"; 1 while <FILE>; $para_count = $.; The sysread solution reads the file a megabyte at a time. Once end-of-file is reached, sysread returns 0. This ends the loop, as does undef, which would indicate an error. The tr operation doesn't really substitute \n for \n in the string; it's an old idiom for counting occurrences of a character in a string. 8.2.4 See AlsoThe tr operator in perlop(1) and Chapter 5 of Programming Perl; your system's wc(1) manpage; the $/ entry in perlvar(1), and in the "Special Variables in Alphabetical Order" section of Chapter 28 of Programming Perl; the Introduction to Chapter 9 |
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