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Re: Re: Large file processed line by line

by coolmichael (Deacon)
on Jun 19, 2001 at 07:01 UTC ( #89537=note: print w/ replies, xml ) Need Help??


in reply to Re: Large file processed line by line
in thread Large file processed line by line

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.


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Re: Re: Re: Large file processed line by line
by btrott (Parson) on Jun 19, 2001 at 07:19 UTC
    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.
Re: Re: Re: Large file processed line by line
by mirod (Canon) on Jun 19, 2001 at 09:54 UTC

    You really should have tested it:

    • -e should be immediatelly followed by the script to run,
    • -p prints the current line, so you don't have to do it yourself, -n is what you want in this case.

    This (tested!) script would work as:

    perl -i.bak -n -e"print if(m/foo/);" foo.txt bar.txt baz.txt

    From perldoc perlrun:

    -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.

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