So I have:
test.pl > test.log
is there a way to know inside test.pl that I am outputing to 'test.log'? At the end of my script I want to do some manipulation of test.log without hardcoding the name.
Maybe. The following works on Linux, but will not be very portable to other systems...
#!/usr/bin/env perl
use strict;
use warnings;
my $out = readlink("/proc/$$/fd/1");
print STDERR "I am being output to $out\n";
Naturally, this is probably a bad idea. Better to explicitly open the file and write to it in Perl, rather than having the shell set up redirections.
You can redirect standard output from perl, with minimal changes to your script,
test.pl test.log
my ($file) = #ARGV;
if (#ARGV) {
open STDOUT, ">", $file or die $!;
}
print "output is redirected to $file\n";
# use $file at the end
Related
I'm trying to open an input file as an argument using the Getopt::Long module
This is the beginning of my script
#! /usr/bin/perl -s
use strict;
use warnings;
use Data::Dumper;
local $Data::Dumper::Useqq = 1;
use Getopt::Long qw(GetOptions);;
my $input='';
GetOptions('input|in=s' => \$input);
open(my $table1,'<', $input) or die "$! - [$input]"; #input file
And this is how I launch the script
$ script.pl -in /path/to/file.txt
I get as output:
No such file or directory - [] at script.pl line 13.
Line 13 is the line with open(....
Is there a mistake in the script?
You are using Perl's built-in option parsing with the -s in your shebang line. In a command like script.pl -in /path/to/file.txt that makes perl set the variable $in to 1 and remove the corresponding entry from #ARGV before Getopt::Long ever sees it
Just remove -s from the shebang line and everything it will work for you
No, there is no mistake in the script. Your code is doing what you told it to do.
It's calling the die "$! - [$input]"; part of that line, because the open returned a false value.
No such file or directory is the content of $!. That's the error it encountered. And between the [] there is the value of $input, which is empty. So there's your problem. You're passing an empty string to open, and that fails.
You are calling it the wrong way.
Getopt::Long requires options that are longer than one letter to be prefixed by --. This means that -in should be --in.
$ script.pl --in /path/to/file.txt
Because you didn't do that, Getopt::Long didn't see your option, and didn't parse it. A bit higher you initialized $input = '', so it stayed the empty string.
You could add a check to make sure that the input file is always provided.
use strict;
use warnings;
use Getopt::Long qw(GetOptions);;
my $input = '';
GetOptions('input|in=s' => \$input);
die 'the --input option is required!' unless $input;
open(my $table1,'<', $input) or die "$! - [$input]"; #input file
I want to search for a string and get the full line from a text file through Perl scripting.
So the text file will be like the following.
data-key-1,col-1.1,col-1.2
data-key-2,col-2.1,col-2.2
data-key-3,col-3.1,col-3.2
Here I want to apply data-key-1 as the search string and get the full line into a Perl variable.
Here I want the exact replacement of grep "data-key-1" data.csv in the shell.
Some syntax like the following worked while running in the console.
perl -wln -e 'print if /\bAPPLE\b/' your_file
But how can I place it in a script? With the perl keyword we can't put it into a script. Is there a way to avoid the loops?
If you'd know the command line options you are giving for your one-liner, you'd know exactly what to write inside your perl script. When you read a file, you need a loop. Choice of loop can yield different results performance wise. Using for loop to read a while is more expensive than using a while loop to read a file.
Your one-liner:
perl -wln -e 'print if /\bAPPLE\b/' your_file
is basically saying:
-w : Use warnings
-l : Chomp the newline character from each line before processing and place it back during printing.
-n : Create an implicit while(<>) { ... } loop to perform an action on each line
-e : Tell perl interpreter to execute the code that follows it.
print if /\bAPPLE\b/ to print entire line if line contains the word APPLE.
So to use the above inside a perl script, you'd do:
#!usr/bin/perl
use strict;
use warnings;
open my $fh, '<', 'your_file' or die "Cannot open file: $!\n";
while(<$fh>) {
my $line = $_ if /\bAPPLE\b/;
# do something with $line
}
chomp is not really required here because you are not doing anything with the line other then checking for an existence of a word.
open($file, "<filename");
while(<$file>) {
print $_ if ($_ =~ /^data-key-3,/);
}
use strict;
use warnings;
# the file name of your .csv file
my $file = 'data.csv';
# open the file for reading
open(FILE, "<$file") or
die("Could not open log file. $!\n");
#process line by line:
while(<FILE>) {
my($line) = $_;
# remove any trail space (the newline)
# not necessary, but again, good habit
chomp($line);
my #result = grep (/data-key-1/, $line);
push (#final, #result);
}
print #final;
I am trying to redirect perl system command to output file with the following code along with time but its not working ??
$cmd="echo hi";
($second, $minute, $hour) = localtime();
$time="$hour:$minute:$second";
system("$time>new.txt");
system("$cmd 1>>new.txt 2>>&1");
If you want to write the variable $time to a text file, open a writeable filehandle and print it to your file instead.
open(my $outfile, '>', 'new.txt');
print $outfile $time;
...
Secondly, your output redirection should read:
1>>new.txt 2>&1
Which means "append STDOUT (1) to new.txt, redirect STDERR (2) to STDOUT (1)". Having >> makes no sense for the second part.
Finally, I (and every other perl programmer) would strongly recommend using strict and warnings pragmas in your scripts. This will help you pick up on any errors or potential problems in your scripting. Once you've done this, all variables must be declared with my, which is a good habit to get in to anyway. So after all that, your script should look something like this:
# recommended pragmas:
use strict;
use warnings;
# declare all new variables with "my"
my $cmd="echo hi";
my ($second, $minute, $hour) = localtime();
my $time="$hour:$minute:$second";
# open a writeable filehandle and print to the filehandle
open(my $outfile, '>', 'new.txt');
print $outfile $time,"\n"; # I've added a newline character here so that
# the time and the command's output are on different lines ;)
system("$cmd 1>>new.txt 2>&1");
Greetings,
I have the following code and am stuck on how I would proceed to modify it so it will ask for the directory, read all files in the directory, then extract specific strings and ouput to an html file? Thanks in advance.
#!/usr/local/bin/perl
use warnings;
use strict;
use Cwd;
print "Enter filename: "; # Should be Enter directory
my $perlfile =STDIN;
open INPUT_FILE, $perlfile || die "Could not open file: $!";
open OUTPUT, '>out.html' || die "Could not open file: $!";
# Evaluates the file and imports it into an array.
my #comment_array = ;
close(INPUT_FILE);
chomp #comment_array;
#comment_array = grep /^\s*#/g, #comment_array;
my $comment;
foreach $comment (#comment_array) {
$comment =~ /####/; #Pattern match to grab only #s
# Prints comments to screen
Print results in html format
# Writes comments to output.html
Writes results to html file
}
close (OUTPUT);
Take it one step at a time. You have a lot planned, but so far you haven't even changed your prompt string to ask for a directory.
To read the entered directory name, your:
my $perlfile =STDIN;
gives an error (under use strict;). Start by looking that error up (use diagnostics; automates this) and trying to figure out what you should be doing instead.
Once you can prompt for a directory name and print it out, then add code to open the directory and read the directory. Directories can be opened and read with opendir and readdir. Make sure you can read the directory and print out the filenames before going on to the next step.
a good starting point to learn about specific functions (from the cmd line)
perldoc -f opendir
However, your particular problem is answered as follows, you can also use command line programs and pipe them into a string to simplify file handling ('cat') and pattern matching ('grep').
#!/usr/bin/perl -w
use strict;
my $dir = "/tmp";
my $dh;
my #patterns;
my $file;
opendir($dh,$dir);
while ($file = readdir($dh)){
if (-f "$dir/$file"){
my $string = `cat $dir/$file | grep pattern123`;
push #patterns, $string;
}
}
closedir($dh);
my $html = join("<br>",#patterns);
open F, ">out.html";
print F $html;
close F;
Is there any method to execute foo2.pl from foo1.pl in Perl, and append the foo2.txt to the foo1.txt then create foo3.txt? thanks.
i.e.
foo1.pl
print "Hello"; # output to foo1.txt;
foo2.pl
print "World"; # output to foo2.txt;
How to create foo3.txt file based on foo1.pl.
foo3.txt
Hello
World
Something like append foo2.txt to foo1.txt.
As i know, I can open foo1.txt and foo2.txt, then include the lines in foo3.pl.
print FOO3_TXT (<FOO1_TXT>);
print FOO3_TXT (<FOO2_TXT>);
Is there any good method?
Update my test (ActivePerl 5.10.1)
My foo.pl
#!C:\Perl\bin\perl.exe
use strict;
use warnings;
print "world\n";
my hw.pl (foo.pl and hw.pl at the same directory)
#!C:\Perl\bin\perl.exe
use strict;
use warnings;
print 'hello ';
print `./foo.pl`;
Output
**D:\learning\perl>hw.pl
hello '.' is not recognized as an internal or external command,
operable program or batch file.**
If hw.pl updated {}:
#!C:\Perl\bin\perl.exe
use strict;
use warnings;
print q{hello }, qx{./foo.pl};
Now Output. (a little different for the loacation of hello)
D:\learning\perl>hw.pl
'.' is not recognized as an internal or external command,
operable program or batch file.
hello
[Update].
Fixed. see answer,
run this as a script
perl foo1.pl > foo3.txt;
perl foo2.pl >> foo3.txt;
contents of foo1.pl
!#/bin/perl
print "Hello";
contents of foo2.pl
!#/bin/perl
print "World";
or
simply use the cat command if you are running linux to append foo2.txt to foo1.txt.
Just in case you are being literal about execute foo2.pl from foo1.pl in Perl then this is what you can do:
print 'hello ';
print qx(perl foo2.pl);
qx is another way to run system commands like backticks. Thus perl foo2.pl is run with the output being sent back to your calling perl script.
So here the same using backticks. Also it uses a direct call to script (which is better):
print 'hello ';
print `./foo2.pl`;
And if you are expecting lots of output from the script then its best not to load it all into memory like above two examples. Instead use open like so:
print 'hello ';
open my $foo2, '-|', './foo2.pl';
print <$foo2>;
close $foo2;
And you can wrap this up into one print statement for "hello world" example:
print 'hello ', do {
open my $foo2, '-|', './foo2.pl';
<$foo2>;
};
/I3az/
Using a shell script (for example, a .bat file on Windows) to run various Perl scripts and combine their output is one way to solve the problem. However, I usually find that Perl itself provides a more powerful and flexible environment than shell scripts. To use Perl in this way, one place to start is by learning about the system and exec commands.
For example:
# In hello.pl
print "Hello\n";
# In world.pl
print "World\n";
# In hello_world.pl.
use strict;
use warnings;
system 'perl hello.pl > hello_world.txt';
system 'perl world.pl >> hello_world.txt';
You can use the following code also
file1.pl
use strict;
use warnings;
open (FH,">file") or die "$! can't open";
print FH "WELCOME\n";
file2.pl
use strict;
use warnings;
open (FH,">>file") or die "$! can't open";
print FH "WELCOME2\n";
The file content is
WELCOME
WELCOME2
If you know beforhand that the script you want to execute from inside the other script is also Perl, you should use do EXPR (https://perldoc.perl.org/functions/do.html).
This executes the contents of the file EXPR in the context of the running perl process and saves you from starting new cmd.exe and perl.exe instances.
hello.pl:
print "Hello";
do "world.pl";
wordl.pl:
print "World";