I have a process which when
executed as below:
process_name > file.txt
will redirect all the output to file.txt and also to the console.
when executed like this
process_name >& file.txt&
will redirect the output to file.txt but will not print the output to console returning the pid on the console.
Now i want to execute the second way of running the process inside a perl script!
how could i do this?
currently i am usng the below method:
#!/usr/bin/perl
use strict;
use warnings;
my $res = `bsm_adjust_controller -F -ra -d 'subnetwork=NETSim_STD/bsc=0005' -f /tmp/31102012/Task_31102012_1421_0005.log >& /tmp/31102012/Ctrl_31102012_1421_0005.log&`;
print $res;
when i run the script it gives:
./temp.pl
sh: /tmp/31102012/Ctrl_31102012_1421_0005.log: bad number
I also tried the below method:
#!/usr/bin/perl
use strict;
use warnings;
my $res = "bsm_adjust_controller -F -ra -d 'subnetwork=NETSim_STD/bsc=0005' -f /tmp/31102012/Task_31102012_1421_0005.log >& /tmp/31102012/Ctrl_31102012_1421_0005.log&";
open(CMD, '-|', $res) || die "couldn't run $res: $!\n";
Even the above script throws the same error.
the purpose is to execute the process in background and continue with the next statements without caring what happened to the process and also i donot need the output of the process being run inside to console.
could anybody please help?
well this worked:
#!/usr/bin/perl
use strict;
use warnings;
my $cmd="bsm_adjust_controller -F -ra -d 'subnetwork=NETSim_STD/bsc=0106' -f /tmp/31102012/Task_31102012_1421_0005.log >/tmp/31102012/Ctrl_31102012_1421_0005.log";
open STDERR, ">/dev/null";
print "Redirected stderr to /dev/null\n";
my $pid=open (FH, "-|",$cmd);
if ($pid) { #parent
print "/tmp/31102012/Task_31102012_1421_0005.log";
exit;
}
print "Redirected stderr to /dev/null\n";
close(FH);
Related
I am trying to use Perl to create a process running bash and then create a file sample.txt, but after the bash command I can't see any output on the console or any sample.txt file in the same directory structure. Can somebody help me to fix following code?
my $var = `bash -l`;
system($var);
print "Done!";
my $filename = 'sample.txt';
open(my $fh, '>', $filename) or die "Could not open file '$filename' $!";
chmod(0777, "sample.txt");
print $fh "hello";
close $fh;
print "Done 1!..";
Bash's -l argument is convincing it to stay interactive. Running:
perl -e 'print `bash -l`'
On its own has the bash process bound to stdin interactively, but the subprocess's output is captured by perl and printed later when bash exits, which it will only do when you press ControlD, issue exit or logout etc.
You probably wanted to start with $var = 'bash -l';. That will start bash interactively at first, and when you exit, will continue the remainder of the program. To me it's unusual to want to do this and I expect you should write something for bash that exits normally, probably with the -c argument.
Replacing your first two lines of code with:
system("bash", "-c", "echo Hello World!");
accomplishes this and the remainder of the program executes normally. I'm unsure what you wanted bash to do for you however. These example cases would be better accomplished with just
system("echo", "Hello World!") or print "Hello World!".
Hi am writing a script which its need to grep the 6th column of the output using awk command but am getting other output.
What is the exact syntax in perl to extract 6th column using awk?
#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;
my $filesystem=`df -h |grep -i dev|grep -vE '^Filesystem|proc|none|udev|tmpfs'`;
print "(\"$filesystem\"|awk '{print \$6}')"
Output :
7831c1c4be8c% ./test.pl
("/dev/disk1 112Gi 43Gi 69Gi 39% 11227595 18084674 38% /
devfs 183Ki 183Ki 0Bi 100% 634 0 100% /dev
"|awk '{print $6}')%
Am trying to remove the % how it can be done ?
7831c1c4be8c% cat test.pl
#!/usr/bin/perl
use warnings;
use strict;
open my $FS, q(df -h |) or die $!;
while (<$FS>) {
print +(split)[4], "\n"
if /dev/i and not /devfs/;
}
7831c1c4be8c% ./test.pl
40%
You don't need awk inside Perl.
#!/usr/bin/perl
use warnings;
use strict;
open my $FS, '-|', q(df -h) or die $!;
while (<$FS>) {
print +(split)[5], "\n"
if /dev/i and not /^Filesystem|proc|none|udev|tmpfs/;
}
as the previous answer says, you don't need awk or grep system calls in perl. however, I will tell you that one reason your code isn't working is because you never made the awk system call. print does not execute the system call. you would have to use system() to execute it.
anyway fwiw you can also do what you want in a one-liner like so:
df -h | perl -lnae 'next if $F[0] =~ /regex/; print $F[5]'
I am new to Perl. I am trying to execute grep command with perl.
I have to read input from a file and based on the input, the grep has to be executed.
My code is as follows:
#!/usr/bin/perl
use warnings;
use strict;
#Reading input files line by line
open FILE, "input.txt" or die $!;
my $lineno = 1;
while (<FILE>) {
print " $_";
#This is what expected.
#our $result=`grep -r Unable Satheesh > out.txt`;
our $result=`grep -r $_ Satheesh > out.txt`;
print $result
}
print "************************************************************\n";
But, if I run the script, it looks like a infinite loop and script is keep on waiting and nothing is printed in the out.txt file.
The reason it's hanging is because you forgot to use chomp after reading from FILE. So there's a newline at the end of $_, and it's executing two shell commands:
grep -r $_
Satheesh > out.txt
Since there's no filename argument to grep, it's reading from standard input, i.e. the terminal. If you type Ctl-d when it hangs, you'll then get an error message telling you that there's no Satheesh command.
Also, since you're redirecting the output of grep to out.txt, nothing gets put in $result. If you want to capture the output in a variable and also put it into the file, you can use the tee command.
Here's the fix:
while (<FILE>) {
print " $_";
chomp;
#This is what expected.
#our $result=`grep -r Unable Satheesh > out.txt`;
our $result=`grep -r $_ Satheesh | tee out.txt`;
print $result
}
I cannot get this to work.
#!/usr/bin/perl -w
use strict;
use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
my $id='123456';
my $filetoopen = '/home/user/public/somefile.txt';
file contains:
123456
234564
364899
437373
So...
A bunch of other subs and code
if(-s $filetoopen){
perl -n -i.bak -e "print unless /^$id$,/" $filetoopen;
}
I need to remove the line that matches $id from file $filetoopen
But, I don't want script to "crash" if $id is not in $filetoopen either.
This is in a .pl scripts sub, not being run from command line.
I think I am close but, after reading for hours here, I had to resort to posting the question.
Will this even work in a script?
I tried TIE with success but, I need to know alternatively how to do this without TIE::FILE.
When I tried I got the error:
syntax error at mylearningcurve.pl line 456, near "bak -e "
Thanks for teaching this old dog...
First of all (this is not the cause of your problem) $, (aka $OUTPUT_FIELD_SEPARATOR) defaults to undef, I'm not sure why you are using it in the regex. I have a feeling the comma was a typo.
It's unclear if you are calling this from a shell script or from Perl?
If from Perl, you should not call a nested Perl interpreter at all.
If the file is small, slurp it in and print:
use File::Slurp;
my #lines = read_file($filename);
write_file($filename, grep { ! /^$id$/ } #lines);
If the file is large, read line by line as a filter.
use File::Copy;
move($filename, "$filename.old") or die "Can not rename: $!\n";
open(my $fh_old, "<", "$filename.old") or die "Can not open $filename.old: $!\n";
open(my $fh, ">", $filename) or die "Can not open $filename: $!\n";
while my $line (<$fh_old>) {
next if $line =~ /^id$/;
print $fh $_;
}
close($fh_old);
close($fh);
If from a shell script, this worked for me:
$ cat x1
123456
234564
364899
437373
$ perl -n -i.bak -e "print unless /^$id$/" x1
$ cat x1
234564
364899
437373
if(-s $filetoopen){
perl -n -i.bak -e "print unless /^$id$,/" $filetoopen;
}
I'm not at all sure what you expect this to do. You can't just put a command line program in the middle of Perl code. You need to use system to call an external program. And Perl is just an external program like any other.
if(-s $filetoopen){
system('perl', '-n -i.bak -e "print unless /^$id$,/"', $filetoopen);
}
The functionality of the -i command line argument can be accessed via $^I.
local #ARGV = $filetoopen;
local $^I = '.bak';
local $_;
while (<>) {
print if !/^$id$/;
}
How can I redirect the STDOUT stream to two files (duplicates) within my Perl script? Currently I am just streaming into a single log file:
open(STDOUT, ">$out_file") or die "Can't open $out_file: $!\n";
What do I have to change? Thx.
You can also use IO::Tee.
use strict;
use warnings;
use IO::Tee;
open(my $fh1,">","tee1") or die $!;
open(my $fh2,">","tee2") or die $!;
my $tee=IO::Tee->new($fh1,$fh2);
select $tee; #This makes $tee the default handle.
print "Hey!\n"; #Because of the select, you don't have to do print $tee "Hey!\n"
And yes, the output works:
> cat tee1
Hey!
> cat tee2
Hey!
Use the tee PerlIO layer.
use PerlIO::Util;
*STDOUT->push_layer(tee => "/tmp/bar");
print "data\n";
$ perl tee_script.pl > /tmp/foo
$ cat /tmp/foo
data
$ cat /tmp/bar
data
File::Tee provides the functionality you need.
use File::Tee qw( tee );
tee(STDOUT, '>', 'stdout.txt');
If you're using a Unix-like system, use the tee utility.
$ perl -le 'print "Hello, world"' | tee /tmp/foo /tmp/bar
Hello, world
$ cat /tmp/foo /tmp/bar
Hello, world
Hello, world
To set up this duplication from within your program, set up a pipe from your STDOUT to an external tee process. Passing "|-" to open makes this easy to do.
#! /usr/bin/env perl
use strict;
use warnings;
my #copies = qw( /tmp/foo /tmp/bar );
open STDOUT, "|-", "tee", #copies or die "$0: tee failed: $!";
print "Hello, world!\n";
close STDOUT or warn "$0: close: $!";
Demo:
$ ./stdout-copies-demo
Hello, world!
$ cat /tmp/foo /tmp/bar
Hello, world!
Hello, world!