Reading and Writing Hash Records to Text Files

Problem

You want to read or write hash records to text files.

If you have an array of records that you'd like to store and retrieve from a text file, you can use a simple format based on mail headers. The format's simplicity requires that the keys have neither colons nor newlines, and the values not have newlines.

This code writes them out:

foreach $record (@Array_of_Records) {
 for $key (sort keys %$record) {
 print "$key: $record->{$key}\n";
}
print "\n";
}

Reading them in is easy, too.

$/ = ""; # paragraph read mode while (<>) {
 my @fields = split /^([^:]+):\s*/m; shift @fields; # for leading null field push(@Array_of_Records, {
 map /(.*)/, @fields });
}

The split acts upon $_ , its default second argument, which contains a full paragraph. The pattern looks for start of line (not just start of record, thanks to the /m) followed by one or more non-colons, followed by a colon and optional white space. When split's pattern contains parentheses, these are returned along with the values. The return values placed in @fields are in key-value order, with a leading null field we shift off. The braces in the call to push produces a reference to a new anonymous hash, which we copy @fields into. Since that array was stored in order of the needed key-value pairing, this makes for well-ordered hash contents.

All you're doing is reading and writing a plain text file, so you can use related recipes for additional components. You could use to ensure that you have clean, concurrent access; to store colons and newlines in keys and values; and store more complex structures.

If you are willing to sacrifice the elegance of a plain textfile for a quick, random-access database of records, use a DBM file, as described in .

Reading and Writing Hash Records to Text Files

Problem

Solution

Discussion

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