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8.2. Counting Lines (or Paragraphs or Records) in a File

You need to compute the number of lines
in a file.

8.2.2. Solution

Many 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. Discussion

Although 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 close d:

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 Also

The 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

8.1. Reading Lines with Continuation Characters		8.3. Processing Every Word in a File

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