Contributed by polr
on Dec 05, 2001 at 20:51 UTC
I am reading in a text file line by line.
If the current line meets certain criteria, I want to modify the previous line.
|Answer: How to (conditionally) modify the previous line based on contents of current line?|
contributed by nothingmuch
Since it's easy to do this with an array — simply look at element at index $i-1 —
you could load the file into an array, process the array, then write the array back out to the file.
Of course, this doesn't scale with the size of the file well.
For a generally application solution, you could map the lines of the file into an array using the module Tie::File:
In this example, I started at index 1 (the second line) because even if the first line (index 0) passes the check, there is no "previous line" to modify.
tie my @array, 'Tie::File', "file.txt"
or die "$!";
for ( my $i = 1; $i <= $#array; $i++ )
if ( check( $array[$i] ) ) # the "current line"
modify( $array[$i-1] );
Please (register and) log in if you wish to add an answer
Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
Read Where should I post X? if you're not absolutely sure you're posting in the right place.
Please read these before you post! —
Posts may use any of the Perl Monks Approved HTML tags:
You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
- a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.
| & || & |
| < || < |
| > || > |
| [ || [ |
| ] || ] ||