The following Perl script prints out its input so that each line begins with a running line number:
#!/usr/bin/perl
$line = 1;
while (<>) {
print $line++, " ", $_; }
The scalar variable $line
is of course the line counter.
The loop construct is of the form
while (<>) {
process one line of input }
Assuming that you have written this script (the simpler version of it) into a
file named lines, you could test it using a command of the form
./lines datafile
In particular, using the script as input to itself, you would do as follows
(the details of system output vary from one system to another):
lk-hp-23 perl 251 % ./lines lines 1 #!/usr/bin/perl 2 $line = 1; 3 while (<>) { 4 print $line++, " ", $_; } lk-hp-23 perl 252 %