I want to patch a binary file with perl. The command doesn't work today, but in the past I used it a lot .
The command below doesn't work on Mac Os X:
perl -pi -e 's|\xA0\x37\x96\x30\xDE\x90|\xA7\x70\x92\x30\xD5\x9B|' /file.bin
If I use
perl -MO=Deparse -pi -e 's|\xA0\x37\x96\x30\xDE\x90|\xA7\x70\x92\x30\xD5\x9B|' /file.bin
the result is:
BEGIN { $^I = ""; }
LINE: while (defined($_ = <ARGV>)) {
s/\xA0\x37\x96\x30\xDE\x90/\247p\2220\325\233/;
}
continue {
die "-p destination: $!\n" unless print $_;
}
-e syntax OK
Why the replace section was modified like this?
I checked 1000 time the syntax is correct; why it doesn't work as expected?
It wasn't modified.
"\xA7\x70\x92\x30\xD5\x9B"
and
"\247p\2220\325\233"
are equivalent.
$ perl -e'CORE::say "\xA7\x70\x92\x30\xD5\x9B" eq "\247p\2220\325\233" ? "same" : "diff"'
same
2478 = A716
p's ASCII encoding is 7016
2228 = 9216
0's ASCII encoding is 3016
3258 = D516
2338 = 9B16
Related
My syntax is
my $pstree = `pstree -p $pid|wc`;
but i am getting an error.
sh: -c: line 1: syntax error near unexpected token `|'
any thoughts?
Your variable $pid isn't just a number; it probably has a trailing newline character.
See it with:
use Data::Dumper;
print Data::Dumper->new([$pid])->Terse(1)->Useqq(1)->Dump;
It's valid perl, your shell is what is complaining. Did you put the #!/bin/perl at the top of the script? It's probably being interpreted by bash, not perl.
host:/var/tmp root# ./try.pl
5992 zsched
6875 /usr/local/sbin/sshd -f /usr/local/etc/sshd_config
3691 /usr/local/sbin/sshd -f /usr/local/etc/sshd_config -R
3711 -tcsh
6084 top 60
===
5 16 175
host:/var/tmp root# cat try.pl
#!/bin/perl
my $pstree = `ptree 3691`;
my $wc = `ptree 3691 | wc`;
print STDOUT $pstree;
print STDOUT "===\n";
print STDOUT $wc;
Instead of using the shell to do your counting, you can use Perl, which saves you a process and some complexity in your shell command:
my $count = () = qx(pstree -p $pid);
qx() does the same thing as backticks. The empty parentheses puts the qx() in list context, which makes it return a list, which then in scalar context is the size. It is a shortcut for:
my #list = qx(pstree -p $pid);
my $count = #list;
I'm writing a Perl script to read a log so that to re-write the file into a new log by removing empty lines in case of seeing any consecutive blank lines of 4 or more. In other words, I'll have to compress any 4 consecutive blank lines (or more lines) into one single line; but any case of 1, 2 or 3 lines in the file will have to remain the format. I have tried to get the solution online but the only I can find is
perl -00 -pe ''
or
perl -00pe0
Also, I see the example in vim like this to delete blocks of 4 empty lines :%s/^\n\{4}// which match what I'm looking for but it was in vim not Perl. Can anyone help in this? Thanks.
To collapse 4+ consecutive Unix-style EOLs to a single newline:
$ perl -0777 -pi.bak -e 's|\n{4,}|\n|g' file.txt
An alternative flavor using look-behind:
$ perl -0777 -pi.bak -e 's|(?<=\n)\n{3,}||g' file.txt
use strict;
use warnings;
my $cnt = 0;
sub flush_ws {
$cnt = 1 if ($cnt >= 4);
while ($cnt > 0) {print "\n"; $cnt--; }
}
while (<>) {
if (/^$/) {
$cnt++;
} else {
flush_ws();
print $_;
}
}
flush_ws();
Your -0 hint is a good one since you can use -0777 to slurp the whole file in -p mode. Read more about these guys in perlrun So this oneliner should do the trick:
$ perl -0777 -pe 's/\n{5,}/\n\n/g'
If there are up to four new lines in a row, nothing happens. Five newlines or more (four empty lines or more) are replaced by two newlines (one empty line). Note the /g switch here to replace not only the first match.
Deparsed code:
BEGIN { $/ = undef; $\ = undef; }
LINE: while (defined($_ = <ARGV>)) {
s/\n{5,}/\n\n/g;
}
continue {
die "-p destination: $!\n" unless print $_;
}
HTH! :)
One way using GNU awk, setting the record separator to NUL:
awk 'BEGIN { RS="\0" } { gsub(/\n{5,}/,"\n")}1' file.txt
This assumes that you're definition of empty excludes whitespace
This will do what you need
perl -ne 'if (/\S/) {$n = 1 if $n >= 4; print "\n" x $n, $_; $n = 0} else {$n++}' myfile
How I can make the following external command within ticks work with variables instead?
Or something similar?
sed -i.bak -e '10,16d;17d' $docname; (this works)
I.e., sed -i.bak -e '$line_number,$line_end_number;$last_line' $docname;
my $result =
qx/sed -i.bak -e "$line_number,${line_end_number}d;${last_line}d" $docname/;
Where the line split avoid the horizontal scroll-bar on SO; otherwise, it would be on one line.
Or, since it is not clear that there's any output to capture:
system "sed -i.back '$line_number,${line_end_number}d;${last_line}d' $docname";
Or you could split that up into arguments yourself:
system "sed", "-i.back", "$line_number,${line_end_number}d;${last_line}d", "$docname";
This tends to be safer since the shell doesn't get a chance to interfere with the interpretation of the arguments.
#args = ("command", "arg1", "arg2");
system(#args) == 0 or die "system #args failed: $?"
Furthermore on the manual:
perldoc -f system
I think you should read up on using qq for strings.
You probably want something like this:
use strict;
use warnings;
my $line_number = qq|10|;
my $line_end_number = qq|16d|;
my $last_line = qq|17d|;
my $doc_name = qq|somefile.bak|;
my $sed_command = qq|sed -i.bak -e '$line_number,$line_end_number;$last_line' $doc_name;|;
print $sed_command;
qx|$sed_command|;
This works:
perl -pi -e 's/abc/cba/g' hellofile
But this does not:
perl -pie 's/cba/abc/g' hellofile
In other words -pi -e works but -pie does not. Why?
The -i flag takes an optional argument (which, if present, must be immediately after it, not in a separate command-line argument) that specifies the suffix to append to the name of the input file for the purposes of creating a backup. Writing perl -pie 's/cba/abc/g' hellofile causes the e to be taken as this suffix, and as the e isn't interpreted as the normal -e option, Perl tries to run the script located in s/cba/abc/g, which probably doesn't exist.
Because -i takes an optional extension for backup files, e.g. -i.bak, and therefore additional flags cannot follow directly after -i.
From perldoc perlrun
-i[extension]
specifies that files processed by the <> construct are to be edited
in-place. It does this by renaming the input file, opening the output
file by the original name, and selecting that output file as the
default for print() statements. The extension, if supplied, is used to
modify the name of the old file to make a backup copy, following these
rules:
If no extension is supplied, no backup is made and the current file is
overwritten.
If the extension doesn't contain a * , then it is appended to the end
of the current filename as a suffix. If the extension does contain one
or more * characters, then each * is replaced with the current
filename. In Perl terms, you could think of this as:
perl already tells you why :) Try-It-To-See
$ perl -pie " s/abc/cba/g " NUL
Can't open perl script " s/abc/cba/g ": No such file or directory
If you use B::Deparse you can see how perl compiles your code
$ perl -MO=Deparse -pi -e " s/abc/cba/g " NUL
BEGIN { $^I = ""; }
LINE: while (defined($_ = <ARGV>)) {
s/abc/cba/g;
}
continue {
die "-p destination: $!\n" unless print $_;
}
-e syntax OK
If you lookup $^I in perlvar you can learn about the -i switch :)
$ perldoc -v "$^I"
$INPLACE_EDIT
$^I The current value of the inplace-edit extension. Use "undef" to
disable inplace editing.
Mnemonic: value of -i switch.
Now if we revisit the first part, add an extra -e, then add Deparse, the -i switch is explained
$ perl -pie -e " s/abc/cba/g " NUL
Can't do inplace edit: NUL is not a regular file.
$ perl -MO=Deparse -pie -e " s/abc/cba/g " NUL
BEGIN { $^I = "e"; }
LINE: while (defined($_ = <ARGV>)) {
s/abc/cba/g;
}
continue {
die "-p destination: $!\n" unless print $_;
}
-e syntax OK
Could it really be that e in -pie is taken as extension? I guess so
$ perl -MO=Deparse -pilogicus -e " s/abc/cba/g " NUL
BEGIN { $^I = "logicus"; }
LINE: while (defined($_ = <ARGV>)) {
s/abc/cba/g;
}
continue {
die "-p destination: $!\n" unless print $_;
}
-e syntax OK
When in doubt, Deparse or Deparse,-p
So at the command line I can conveniently do something like this:
perl -pne 's/from/to/' in > out
And if I need to repeat this and/or I have several other perl -pne transformations, I can put them in, say, a .bat file in Windows. That's a rather roundabout way of doing it, of course. I should just write one perl script that has all those regex transformations.
So how do you write it? If I have a shell script containing these lines:
perl -pne 's/from1/to1/' in > temp
perl -pne 's/from2/to2/' -i temp
perl -pne 's/from3/to3/' -i temp
perl -pne 's/from4/to4/' -i temp
perl -pne 's/from5/to5/' temp > out
How can I just put these all into one perl script?
-e accepts arbitrary complex program. So just join your substitution operations.
perl -pe 's/from1/to1/; s/from2/to2/; s/from3/to3/; s/from4/to4/; s/from5/to5/' in > out
If you really want a Perl program that handles input and looping explicitely, deparse the one-liner to see the generated code and work from here.
> perl -MO=Deparse -pe 's/from1/to1/; s/from2/to2/; s/from3/to3/; s/from4/to4/; s/from5/to5/'
LINE: while (defined($_ = <ARGV>)) {
s/from1/to1/;
s/from2/to2/;
s/from3/to3/;
s/from4/to4/;
s/from5/to5/;
}
continue {
print $_;
}
-e syntax OK
Related answer to the question you didn't quite ask: the perl special variable $^I, used together with #ARGV, gives the in-place editing behavior of -i. As with the -p option, Deparse will show the generated code:
perl -MO=Deparse -pi.bak -le 's/foo/bar/'
BEGIN { $^I = ".bak"; }
BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined($_ = <ARGV>)) {
chomp $_;
s/foo/bar/;
}
continue {
print $_;
}