Reading from a file and in the same moment writing to it is rarely what you want to do. Consider a file to be much like a vinyl record - the read-write head moves forward. If you read a line, the read-write head is now at the end of that line. You then write your modified line to it. This likely is not what you want.

I recommend either slurping the whole file into memory before modifying, then writing it out as a whole again. Alternatively you can use Tie::File, which allows you to treat a file as an array. The most sane solution would be to use a templating module, like Template Toolkit for example.

perl -pi -e 's/(SOURCEREPOSITORYNAME)/$1=Development/g' y:\perl\test.c
+tl
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The -i command-line switch modifies each file in place. It does so by creating a temporary file (but Perl takes care of the details/bookkeeping).

You can also do this yourself of course:

open(OLD, "< $old")       or die "can't open $old: $!";
open(NEW, "> $new")       or die "can't open $new: $!";
while (<OLD>) {
    # change $_, then...
    print NEW $_          or die "can't write $new: $!";
}
close(OLD)                or die "can't close $old: $!";
close(NEW)                or die "can't close $new: $!";
rename($old, "$old.orig") or die "can't rename $old to $old.orig: $!";
rename($new, $old)        or die "can't rename $new to $old: $!";
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Source Perl Cookbook.

You are getting the funny output because you are using buffered I/O on the file and you are neither flushing the buffers nor setting the file position when you switch from reading to writing.

When you read the first line from the file, perl actually reads a buffer full of data. Your file is very small so it fits in the buffer and is read in a single read from the system. Perl then returns the first line from the buffer to your program, leaving the file position at the next character: the start of the second line. The buffer contains the entire file:

Dit is een voorbeeldtekst
The quick brown fox jumps over the lazy dog.
SOURCEREPOSITORYNAME
Roses are red, violets are blue
And Osama Is coming To Kill you
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thanks for the explanation!
I solved my little problem by just opening the handle two times: one for read and one for write access:


#!perl -w

use strict;
my $line;
my @array;
my $CTLfile = 'y:\perl\test.ctl';
open (CTLHANDLE, "<$CTLfile");
@array = <CTLHANDLE>;
close(CTLHANDLE);
open (CTLHANDLE, ">$CTLfile");
foreach $line(@array){
    $line =~ s/SOURCEREPOSITORYNAME/SOURCEREPOSITORYNAME=Development/g
+;
    print CTLHANDLE "$line";
}
close(CTLHANDLE);
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this seems to work fine.

That will work well for small to moderately sized files: anything that fits in memory, which is quite large these days.It is a good solution in many cases.

An advantage of writing to a temporary file and renaming is that you are less likely to end up with a truncated or partial file replacing your original. With your method, if your program or the system fails after you open the file for output, which truncates it, and before you finish writing and flushing all your buffers to disk, you will end up with an incomplete file. If you write to a temporary file and only rename it after closing your output file handle the risk of ending up with a truncated file is much much less.

There is still some risk, even if you write a temporary file, close and rename it. You can reduce the risk further, but not to zero as far as I can tell. Through the various layers of control between your program and the persistent storage medium, it is possible that operations are re-ordered and that abrupt termination (e.g. power loss) can result in corruption despite even extreme measures taken in your program. http://www.gossamer-threads.com/lists/perl/porters/236839 is one writeup on some of these issues.

-bib

# replace all occurrences in the file
edit_file { s/foo/bar/gs } myfile.txt> 
# replace occurrences a line at a time
edit_file_lines { s/foo/bar/g } myfile.txt>
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File::Slurp is no longer recommended. TLDR: It doesn't work well with encodings, is poorly maintained, and its default options are seldom needed.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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