I have a code that looks like this
sub ConvertDosToUnix{
my $file = shift;
open my $dosFile, '>', $file or die "\nERROR: Cannot open $file";
select $dosFile;
print("Converting Dos To Unix");
`perl -p -i -e "s/\r//g" $dosFile`;
close $dosFile;
}
Also, the perl command works when I used that outside the subroutine or in the main function. But when I created a separate subroutine for converting dos to unix, I got an error that says:
sh: -c: line 0: syntax error near unexpected token `('
//g" GLOB(0x148b990)' -p -i -e "s/
In which I don't understand.
Also, I also tried dos2unix but for some reason, it doesn't totally remove all the carriage returns like the perl command.
Honestly, you seem a little confused.
The code you have inside backticks is a command that is run by the shell. It needs to be passed a filename. You have your filename in the variable $file, but you pass it the variable $dosFile which contains a file handle (which stringifies to "GLOB(0x148b990)" - hence your error message).
So all your work opening the file is wasted. Really, all you wanted was:
`perl -p -i -e "s/\r//g" $file`
But your system almost certainly has dos2unix installed.
`dos2unix $file`
I should also point out that using backticks is only necessary if you want to capture the output from the command. If, as in this case, you don't need the output, then you should use system() instead.
system('dos2unix', $file);
Related
I want to execute some code before execution(redirect stderr to stdout).
perl -e "BEGIN {open STDERR, '>&STDOUT'}" perl.pl
But when there is -e, no file will be executed. I know $Config{sitelib}/sitecustomize.pl can pre-execute some code, and -f option can disable it. But this way is inflexible. In most cases, I do not need to add extra code. I don't want to add -f every time.
I cannot use shell to redirect. I want to set org-babel-perl-command in emacs org mode so that stdout and stderr can be printed in the same way, instead of opening another window to print stderr. org-babel-perl-command should be like perl.
For example, org-babel-python-command can be set to python -i -c "import sys; sys.stderr = sys.stdout".
perl -e'
open( STDERR, ">&STDOUT" );
do( shift( #ARGV ) );
' perl.pl
(Error handling needed.)
For the case in question, the following would suffice:
perl perl.pl 2>&1
Maybe even
./perl.pl 2>&1
You could just make a wrapper for perl. For example:
#!/bin/bash
exec perl "$#" 2>&1
Then make it executable and use instead of perl in your org-babel-perl-command. Ensure it can be found in your PATH or use full location.
If I have this inline command:
perl -pi -e 's/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'
Which is simply to substitute four-digit hex, and add it a 'x' in front. -i used with no filenames on the command line, reading from STDIN. So for params: 0000 0776, results are \x00\x00\x07\x76
I know, that if -n or -p (with printing) called, perl takes <> diamond. But I want to pass args only AFTER command, but perl assumes it as files to read. So how do I force -n or -p to regard args after command to be regular args for <> in program, and not args as files to read?
Also, I do not understand the role of i here. If i would not include it, then I would be adding args line after line (as does <>), but with i, it takes all my args at once?
If there are no arguments (i.e., if #ARGV is empty), then your one-line script (which implicitly uses <>) will read input from STDIN. So the solution is to clear #ARGV at compile time.
perl -pi -e 'BEGIN{#ARGV=()}
s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'
Another solution: Force ARGV (the implicit file handle that the base <> operator reads from) to point to STDIN. This solution doesn't clobber your #ARGV, if any.
perl -pi -e 'BEGIN{*ARGV=*STDIN}
s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'
The -p option is equivalent to the following code:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
-n is the same without the continue block. There's no way to change what it reads from (which is unfortunate, since <<>> and <STDIN> are both safer options), but it's pretty easy to replicate it with your modification (the error checking is rarely necessary here):
perl -e 'while (<STDIN>) { s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g } continue { print }'
I am not familiar with perl. I am reading an installation guide atm and the following Linux command has come up:
perl -p -i -e "s/enforcing/disabled/" /etc/selinux/config
Now, I am trying to understand this. Here is my understanding so far:
-e simply allows for executing whatever follows
-p puts my commands that follow -e in a loop. Now this is strange to me, as to me this command seems to be trying to say: Write "s/enforcing/disabled/" into /etc/selinux/config. Then again, where is the "write" command? And what is this -i (inline) good for?
-p changes
s/enforcing/disabled/
to something equivalent to
while (<>) {
s/enforcing/disabled/;
print;
}
which is short for
while (defined( $_ = <ARGV> )) {
$_ =~ s/enforcing/disabled/;
print($_);
}
What this does:
It reads a line from ARGV into $_. ARGV is a special file handle that reads from the each of the files specified as arguments (or STDIN if no files are provided).
If EOF has been reached, the loop and therefore the program exits.
It replaces the first occurrence of enforcing with disabled.
It prints out the modified line to the default output handle. Because of -i, this is a handle to a new file with the same name as the one from which the program is currently reading.*
Repeat.
For example,
$ cat a
foo
bar enforcing the law
baz
enforcing enforcing
$ perl -pe's/enforcing/disabled/' -i a
$ cat a
foo
bar disabled the law
baz
disabled enforcing
* — In old versions of Perl, the old file has already been deleted at this point, but it's still accessible as long as there's an open file handle to it. In very new versions of Perl, this writes to temporary file that will later overwrite the file from which the program is reading.
To find out exactly what Perl is going to do, you can use the O module
perl -MO=Deparse -p -i -e "s/enforcing/disabled/" file
outputs
BEGIN { $^I = ""; }
LINE: while (defined($_ = readline ARGV)) {
s/enforcing/disabled/;
}
continue {
die "-p destination: $!\n" unless print $_;
}
-e syntax OK
I have a situation where I need to detect if a particular perl executable, /usr/goofy/bin/perl exists and if so use it to run the Perl script otherwise use /usr/bin/perl.
I have been struggling with this small POC script, called perlshebang.pl:
#!/bin/sh -e
perls="/usr/goofy/bin/perl /usr/bin/perl"
for pl_exec in $perls
do
if [ -x $pl_exec ]; then
exec "$pl_exec -w -S \"$0\" ${1+\"$#\"}"
fi
done
print "[$^X] Whoop!\n";
When I run this on a system that does not have /usr/goofy/bin/perl I get this error message:
./perlshebang.pl: 6: exec: /usr/bin/perl -w -S "./perlshebang.pl" : not found
And when I run it on a system that does have /usr/goofy/bin/perl I get a similuar error message:
./perlshebang.pl: line 6: /usr/goofy/bin/perl -w -S "./perlshebang.pl" : No such file or directory
I think I am close but cannot figure out why I am getting these error messages.
Thanks!
To answer your question, "Why am I getting these error messages?", the problem is your exec line:
exec "/path/to/cmd arg arg"
# This will attempt to execute a file named "cmd arg arg"
# (with spaces in name) in directory /path/to/
Contrast that with
exec /path/to/cmd arg arg
# This will attempt to execute a file named "cmd" in directory
# /path/to/, with arguments "arg" and "arg"
So, that is why the shell complains that it cannot find your executable. You don't have a file named perl -w -s "perlshebang.pl", neither under /usr/bin/ nor under /usr/goofy/bin/.
This sounds a little ugly to me if you are releasing software that uses this hack
If you have no other choice, then I suggest you make sure there is always a /usr/goofy/bin/perl, and use the shebang line
#!/usr/goofy/bin/perl
on all your scripts.
For those systems where you want to use the system perl, just make /usr/goofy/bin/perl a symlink to /usr/bin/perl
A co-worker of mine came up with this. I am not sure I fully understand it but it seems to work fine:
#!/bin/sh
#! -*-perl-*-
eval ' if test -x /usr/goofy/bin/perl ; then
exec /usr/goofy/bin/perl -x -S $0 ${1+"$#"};
elif test -x /usr/bin/perl ; then
exec /usr/bin/perl -x -S $0 ${1+"$#"};
fi '
if $running_under_some_shell;
use strict;
use warnings;
print "hello world\n"; # if $foo;
printf("running %s v(%vd)\n", $^X, $^V);
__END__
unpod like docs.
See http://perldoc.perl.org/perlrun.html
You can run the idea out of a Perl script running /usr/bin/perl. Use the shebang line with the 'goofy perl' in your script that should run. Then run the following wrapper, followed by the normal invocation of the script (its name and arguments).
#!/usr/bin/perl
exec "#ARGV";
exec "/usr/bin/perl #ARGV";
print STDERR "Couldn't execute either.\n";
Let's call the above pick_perl.pl, and your script is script.pl. Run it all as
pick_perl.pl script.pl args-for-script
The exec replaces the running program altogether with the one it executes, ie. it loads the new program. Thus your script runs with its own shebang. If that failes exec returns quietly (with false) and the next statement is executed so the other Perl runs the script (overriding the shebang). This happens if script's shebang fails, but also if the first exec fails to execute for any reason.
If you wish/need to run checks then put exec in a full if block. One can also interrogate the 'goofy_perl' file further if -e isn't assuring enough.
#!/usr/bin/perl
$system_perl = "/usr/bin/perl";
$goofy_perl = "/usr/goofy/bin/perl";
# Your 'goofy_perl' script with its arguments
#script_cmd = #ARGV;
if (-x $goofy_perl) { exec "#script_cmd" }
exec "$system_perl #script_cmd";
The #script_cmd has the full command line for your script (which has 'goofy_perl' shebang).
How can i remove first line of txt file in perl script?
`sed "1d" filename.txt`
Dosen't work.
You can use Tie::File:
use Tie::File;
tie #array, 'Tie::File', $filename or die $!;
shift #array;
untie #array;
`sed 1d filename.txt > newfile.txt`
should work. If you don't redirect it to a file, it will just read the whole file minus the first line to stdout.
That sends to the output to sed's STDOUT (which Perl proceeds to capture into a variable) instead of filename.txt. You want to use sed's -i.
sed -i "1d" filename.txt
Since there's no output to capture, it makes no sense to use backticks. You want system.
system('sed -i "1d" filename.txt');
Better: (Avoids launching another shell)
system('sed', '-i', '1d', 'filename.txt');
Best: (Does error checking for you)
use IPC::System::Simple qw( systemx );
systemx('sed', '-i', '1d', 'filename.txt');
Because you're doing this using an inline sed, here is a Perl equiv..
perl -ne'$.==1?next:print' <(seq 1 10)
Where the options mean,
-n assume "while (<>) { ... }" loop around program
-e program one line of program (several -e's allowed, omit programfile)
Other notes,
$. is the variable for the current line number.
<() is Bash voodoo for generating a FIFO in the background.