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Replace Last Line in File
by kevinw (Novice) on Aug 07, 2002 at 14:19 UTC
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perl -pi -we '($_,$@)=($@,$_);$_.="New line\n"if eof' your_file
Abigail | [reply]
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Why not <code>perl -pi -we '$_="New line\n"if eof' your_file<code>
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perldoc -q change line file
perl 5.008 will tell you to use Tie::File, older perls offer other examples.
~Particle *accelerates*
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Re: search and replace last line
by waswas-fng (Curate) on Aug 07, 2002 at 15:50 UTC
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Depends if the file is small enough to fit into memory, if it is here ya go..
-Waswas
#!/usr/local/bin/perl
my @fileslurp = ();
my $datefld = "";
my $testdate = "200208";
my $newline = "Not the old date\n";
my $thisfile = "/var/tmp/junk.log";
open (FILE,"$thisfile");
@fileslurp = <FILE>;
close FILE;
($datefld) = split(/ /,@fileslurp[$#fileslurp]);
@fileslurp[$#fileslurp] = $newline if ($datefld eq "$testdate") ;
foreach $x (@fileslurp) {
print $x;
}
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thanks....what is the easiest way to replace the last line of the file?
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If you don't want to do the traditional approach of buffering and re-writing the data yourself, you can try Tie::File. A small example using your test data:
#!/usr/bin/perl -wd
use Tie::File;
tie @array, 'Tie::File', "test.txt" or die "cannot tie file\n";
($date,$data) = split( /\s+/, $array[-1] );
$data = "whatever" if $date eq "200208";
$array[-1] = "$date $data";
untie @array;
-derby | [reply]
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Re: search and replace last line
by abitkin (Monk) on Aug 07, 2002 at 15:41 UTC
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Why don't you use tail to get the last line, compair that, then if you need to alter it (I recomend using nl to get the number of lines) use head with the number of lines - 1 plus your line.
eg.
perl addline.pl -f test.dat
# Get the file through get opt
my $line = `nl $file | tail -n 1`;
my @items = ($line =~ /^\s*([0-9]+)\s+([0-9]+)\s+/);
my $lineNum = int($items[0]) - 1;
my $newDate = $items[1];
my $fileTmp = $file . ".tmp";
if($date eq $newDate){
system("head -n $lineNum $file > $fileTmp");
system("echo $newline >> $fileTmp");
system("rm $file;mv $fileTmp $file");
}
I haven't compiled this, but you should have an idea of how this works.
ps. if you're doing this on windows, download cygwin and use the nl, tail, and head that they have in their packages. (They are exes, and will work with system.) | [reply]
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Re: search and replace last line
by kschwab (Vicar) on Aug 09, 2002 at 14:01 UTC
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If this file can get large, you may get some benefit
out of not rewriting the whole file.
#!/usr/bin/perl
my $file=shift(@ARGV);
open(FILE,"+<$file") or die;
while (<FILE>) {
if (eof(FILE)) {
seek(FILE,-(length($_)),2) or die("$!\n");
print FILE "replacement string\n";
last;
}
}
close FILE;
Note that you don't really have to read the whole
file either. You could seek() to the end
and then back up looking for a newline. Or, if
each line is the same length ( it appears that they
may be...), you can just go the end and back up
X bytes.
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