Write to file

jriggs420 has asked for the wisdom of the Perl Monks concerning the following question:

Hello again, I know that it's possible to create a file, and then write too it fairly easily in perl. But what about writing to a file that already exists, I have I notion that this must be possible. I'd like to take it a step further; Is it possible to write to a specified spot in a file, (not the beginning or end...the middle). If so, can the write location determined by linenum or by regexs, or (hopefully) either/both.
I know that you can overwrite any/all text w/ perl by using the '>$file' (or '>>$file' to append) open method, but what about just overwriting certain specified lines? Any generic code or links would be must appreciated, TIA, Average Joe user.

Comment on Write to file

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Re: Write to file by Fletch (Bishop) on Oct 17, 2005 at 18:59 UTC
`freebie:~ 716> perldoc -q 'delete a line' Found in /System/Library/Perl/5.8.6/pods/perlfaq5.pod How do I change one line in a file/delete a line in a file/inse +rt a line in the middle of a file/append to the beginning of a file? Use the Tie::File module, which is included in the standard dis +tribu- tion since Perl 5.8.0.` [download]	[reply] [d/l]
Re: Write to file by ikegami (Patriarch) on Oct 17, 2005 at 20:27 UTC
As mentioned (indirectly) by Fletch, Tie::File probably fits your needs best. It allows you to treat a file as an array. Anything you do to the array will be reflected by the file. I just wanted to provide some usage tips: To remove a line from the file, use `splice`. For example, `splice(@tied_to_file, 10, 1);` removes one line, starting with the 11th one (0-based indexes). `splice` is also used to insert lines. For example, `splice(@tied_to_file, 10, 0, @lines_to_insert);` inserts the provided lines before the 11th line (0-based indexes). You can use `grep` to apply filters to every line of your file. For example, `@tied_to_file = grep { !/DELETE ME/ } @tied_to_file;` You can use `map` to apply transformations to every line of your file. For example, `@tied_to_file = map { uc($_) } @tied_to_file;`	[reply] [d/l] [select]
Re: Write to file by blue_cowdawg (Monsignor) on Oct 17, 2005 at 20:25 UTC
I'd like to take it a step further; Is it possible to write to a specified spot in a file, (not the beginning or end...the middle). Take a look at Tie::File and see what you think. It allows you to treat a file as if it were an array and do the the file anything else you would do to an array of scalars. Peter L. Berghold -- Unix Professional Peter -at- Berghold -dot- Net; AOL IM redcowdawg Yahoo IM: blue_cowdawg	[reply]
Re: Write to file by Trix606 (Monk) on Oct 17, 2005 at 18:56 UTC
It sounds like seek or sysseek is what you are looking for.	[reply]
Re^2: Write to file by jriggs420 (Sexton) on Oct 17, 2005 at 18:58 UTC
I thought seek was only to find the beginning and/or end of a file?	[reply]
Re^3: Write to file by Fletch (Bishop) on Oct 17, 2005 at 19:01 UTC
`seek` will allow you to position the file pointer to any offset within the file. The problem is that files are ordered sequences of octets, not lines. Unless you're dealing with fixed line lengths you're more than likely going to overwrite something if you try and do things in place yourself. You want to use the module mentioned in the FAQ I've referenced.	[reply] [d/l]