The general idiom is to use a while loop to iterate
over the lines in the file, reading in one line at a time
and processing it, then moving on to the next.
Something like this:
open FH, "foo" or die "Can't open foo: $!";
while (<FH>) {
## current line is in $_, process it
}
close FH or warn "Error closing foo: $!";
Depending on your situation, you might also want to
check out the -p and -n command
line flags to perl (perlrun).
If these are files specified on the command line,
you can use the special construct:
while (<>) {
## line is in $_
}
This might be useful in a situation like
$ process.pl foo.txt bar.txt baz.txt
to process each of the files on the command line. | [reply] [Watch: Dir/Any] [d/l] [select] |
Don't forget about the everfaithful -i.bak command line flag. It's one of my favourites. It edits a file "inplace" one line at a time. This should delete everything that doesn't contain the string "foo" (but I haven't tested it. sorry)
perl -epi.bak "print if(m/foo/);" foo.txt bar.txt baz.txt
Update: Read on for the correct answer. I really should have tested it. Thanks Mirod and Btrott. ++ to both of you. -- for me. | [reply] [Watch: Dir/Any] [d/l] |
-n causes Perl to assume the following loop around your
program, which makes it iterate over filename
arguments somewhat like sed -n or awk:
LINE:
while (<>) {
... # your program goes here
}
"BEGIN" and "END" blocks may be used to capture
control before or after the implicit program loop,
just as in awk.
-p causes Perl to assume the following loop around your
program, which makes it iterate over filename
arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for
some reason, Perl warns you about it, and moves on to
the next file. Note that the lines are printed
automatically. An error occurring during printing is
treated as fatal. To suppress printing use the -n
switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture
control before or after the implicit loop, just as in
awk.
| [reply] [Watch: Dir/Any] [d/l] [select] |
Right, -i is quite cool. But all -i does is open
the file for in-place editing; it doesn't "edit the file one line at
a time". If you notice, you also have the -p option in
the above command line; that's actually the switch that's
doing the line-by-line processing.
| [reply] [Watch: Dir/Any] |