Re: How can I replace a single character (digit) in a file

Here's one way to do it, supposing you wanted to change the number after "pref3" from 0 to 9:

open(PREF,"+< preffile") or die;

while (<PREF>) {
    # if we see pref3 set to 0
    if (/^pref3\t0$/) {
        # you need to rewind two chars to get 
        # before the 0 and the newline , which 
        # you've already gone past
        seek(PREF,-2,1) or die;
        # print a "9" in this spot
        print PREF "9";
        # move forward one char past the newline
        # to continue reading.
        seek(PREF,1,1) or die;
    }
}
close PREF;
[download]

See open for the <+ read-write mode, and seek for the seek() bit.

Update: I should note that this only works when the replacement string is the same length as the original. See "perldoc -q 'how do I change one line'" for a complete answer.

Update2:Replaced the read() with while(<PREF>), since it's not likely that all the lines in the file are 8 chars long.

Comment on Re: How can I replace a single character (digit) in a file Download Code

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Re: Re: How can I replace a single character (digit) in a file by sofreshsoclean (Initiate) on Jul 30, 2001 at 05:52 UTC
Thanks for your guidance, the seek command worked like a charm. Here's what I ended up using: `open THIS_FILE, "+<$listOption" or die "ERROR: SearchFile: $!"; while (<THIS_FILE>) { if (/^$genre\t\d$/) { seek(THIS_FILE, -2, 1) or die; print THIS_FILE $option; seek(THIS_FILE, 1, 1) or die; } } close THIS_FILE;` [download] Pretty close to what you updated to. It took me a while to realize I shouldn't be using the 8 char read. Thanx -Zach (SFSC)	[reply] [d/l]
Re: Re: How can I replace a single character (digit) in a file by ides (Deacon) on Jul 30, 2001 at 01:20 UTC
This is a much better solution than mine. :) ----------------------------------- Frank Wiles <frank@wiles.org> http://frank.wiles.org	[reply]