I'm trying to make a very simple script to call the PDFXchange viewer from a .desktop file. But I'm not able to do this because the bash is seeing things that I'm not aware:
#!/usr/bin/perl
use strict;
use warnings;
my $winepath = `winepath -w -0 "$ARGV[0]"`;
my $cmd=join ' ',
'wine',
'\'C:\Program Files\Tracker Software\PDF Viewer\PDFXCview.exe\'',
"\'$winepath\'";
print $cmd . "\\n";
exec $cmd;
Output
$ exec_pdfxcv 'pdf with spaces.pdf'
wine 'C:\Program Files\Tracker Software\PDF Viewer\PDFXCview.exe' 'Z:\media\FILES\pdf with spaces.pdf'\nsh: 1: Syntax error: Unterminated quoted string
I'm very beginner at Perl, so I run out of ideas very quickly after tried a couple of times with different quotes configurations.
It seems that you dodged the bullet (of the common inscrutable mangle of quotes and escapes) here, since you don't need the shell for what is done and the rest doesn't need much either.
Then use the list-form of exec, which bypasses the shell altogether. This can be done with system as well but, alas, not with backticks.
my $winepath = `winepath -w -0 "$ARGV[0]"`;
chomp $winepath;
my #cmd = (
'wine',
q('C:\Program Files\Tracker Software\PDF Viewer\PDFXCview.exe'),
"'$winepath'"
);
exec #cmd;
Note the use of the q() operator as single quotes, freeing the symbol ' for use inside.
We should remove the newline from $winepath (returned by qx) and need to protect spaces inside it by adding ' around it.
Going through the shell only makes it harder; do it only when you specifically need the shell.
Once you do need the shell, however, be aware of String::ShellQuote and Win32::ShellQuote.
Finally, work through Quoting the Shell from Perl.com. A required reading in my opinion.
I finally make it work after a hundred of tries.
#!/usr/bin/perl
use strict;
use warnings;
my $winepath = `winepath -w -0 "$ARGV[0]"`;
exec 'wine', q(C:\Program Files\Tracker Software\PDF Viewer\PDFXCview.exe), "".$winepath."";
I hope help someone!
If there is anyone interested in the .desktop file:
[Desktop Entry]
Name=PDF XChange Viwer
Comment=View multi-page documents
Exec=exec_pdfxcv %U
StartupNotify=true
Terminal=false
Type=Application
StartupWMClass=PDFXCview.exe
Icon=evince
Categories=GNOME;GTK;Office;Viewer;
MimeType=application/pdf;application/x-bzpdf;application/x-gzpdf;application/x-xzpdf;application/x-ext-pdf;application/postscript;application/x-bzpostscript;application/x-gzpostscript;image/x-eps;image/x-bzeps;image/x-gzeps;application/x-ext-ps;application/x-ext-eps;application/x-dvi;application/x-bzdvi;application/x-gzdvi;application/x-ext-dvi;image/vnd.djvu;image/vnd.djvu+multipage;application/x-ext-djv;application/x-ext-djvu;image/tiff;application/x-cbr;application/x-cbz;application/x-cb7;application/x-cbt;application/x-ext-cbr;application/x-ext-cbz;application/vnd.comicbook+zip;application/x-ext-cb7;application/x-ext-cbt;application/oxps;application/vnd.ms-xpsdocument;
Related
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($command, #arguments);
For example:
system("sh", "script.sh", "--help" );
system("sh script.sh --help");
System will execute the $command with
#arguments and return to your script when finished. You may check $!
for certain errors passed to the OS by the external application. Read
the documentation for system for the nuances of how various
invocations are slightly different.
2. Using exec
This is very similar to the use of system, but it will
terminate your script upon execution. Again, read the documentation
for exec for more.
3. Using backticks or qx//
my $output = `script.sh --option`;
my $output = qx/script.sh --option/;
The backtick operator and it's equivalent qx//, excute the command and options inside the operator and return that commands output to STDOUT when it finishes.
There are also ways to run external applications through creative use of open, but this is advanced use; read the documentation for more.
From Perl HowTo, the most common ways to execute external commands from Perl are:
my $files = `ls -la` — captures the output of the command in $files
system "touch ~/foo" — if you don't want to capture the command's output
exec "vim ~/foo" — if you don't want to return to the script after executing the command
open(my $file, '|-', "grep foo"); print $file "foo\nbar" — if you want to pipe input into the command
Examples
`ls -l`;
system("ls -l");
exec("ls -l");
Look at the open function in Perl - especially the variants using a '|' (pipe) in the arguments. Done correctly, you'll get a file handle that you can use to read the output of the command. The back tick operators also do this.
You might also want to review whether Perl has access to the C functions that the command itself uses. For example, for ls -a, you could use the opendir function, and then read the file names with the readdir function, and finally close the directory with (surprise) the closedir function. This has a number of benefits - precision probably being more important than speed. Using these functions, you can get the correct data even if the file names contain odd characters like newline.
As you become more experienced with using Perl, you'll find that there are fewer and fewer occasions when you need to run shell commands. For example, one way to get a list of files is to use Perl's built-in glob function. If you want the list in sorted order you could combine it with the built-in sort function. If you want details about each file, you can use the stat function. Here's an example:
#!/usr/bin/perl
use strict;
use warnings;
foreach my $file ( sort glob('/home/grant/*') ) {
my($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks)
= stat($file);
printf("%-40s %8u bytes\n", $file, $size);
}
There are a lot of ways you can call a shell command from a Perl script, such as:
back tick
ls which captures the output and gives back to you.
system
system('ls');
open
Refer #17 here: Perl programming tips
You might want to look into open2 and open3 in case you need bidirectional communication.
I have been using system and qq to run linux programs inside perl. And it has worked well.
#!/usr/bin/perl # A hashbang line in perl
use strict; # It can save you a lot of time and headache
use warnings; # It helps you find typing mistakes
# my keyword in Perl declares the listed variable
my $adduser = '/usr/sbin/adduser';
my $edquota = '/usr/sbin/edquota';
my $chage = '/usr/bin/chage';
my $quota = '/usr/bin/quota';
my $nomeinteiro;
my $username;
my $home;
# system() function executes a system shell command
# qq() can be used in place of double quotes
system qq($adduser --home $home --gecos "$fullname" $username);
system qq($edquota -p john $username);
system qq($chage -E \$(date -d +180days +%Y-%m-%d) $username);
system qq($chage -l $username);
system qq($quota -s $username);
When I do in perl script (source):
`perl -d:DebugHooks::DbInteract='s;e [\#DB::stack\,\#DB::goto_frames]' -e '1'`
The module gets two arguments:
s;e [\#DB::goto_frames\
\#DB::stack];
But I want to get only one:
s;e [\#DB::goto_frames,\#DB::stack];
How to escape ',' sign?
It's got to be your module splitting on the comma, not perl or the shell. Running the following under bash, I get only a single argument in #ARGV:
$ perl -w -E 'say join "\n", ("---", #ARGV, "---")' 's;e [\#DB::stack\,\#DB::goto_frames]'
---
s;e [\#DB::stack\,\#DB::goto_frames]
---
Edit:
I stand corrected. It is being split on commas by perl, presumably to allow passing multiple arguments to a module, as I proved to myself by creating a module at ./Devel/DbInteract.pm containing:
package Devel::DbInteract;
use strict;
use warnings;
use 5.010;
sub import {
say 'Received ' . scalar #_ . ' params:';
say join "\n", #_;
}
1;
and running the command:
$ PERL5LIB=. perl -d:DbInteract='s;e [\#DB::stack,\#DB::goto_frames]' -e ''
Received 3 params:
Devel::DbInteract
s;e [\#DB::stack
\#DB::goto_frames]
Judging by the source linked in the asker's answer, there does not appear to be any provision for escaping values or any other way to prevent this splitting. Your options, then, would be to either work around it by joining the params back together or submitting a patch to the perl source to add an allowance for escaping.
Perl does not care about escaping: https://github.com/Perl/perl5/blob/blead/perl.c#L3240-L3264
the -d flag just add next as zero line number into the script:
use Devel::DbInteract split(/,/,q{s;e [\#DB::stack\,\#DB::goto_frames]});
Some people advice me simple approach than patching perl. Just to use => in my case:
`perl -d:DebugHooks::DbInteract='s;e [\#DB::stack => \#DB::goto_frames]' -e '1'`
When I run the ls command this runs fine. But echo $PATH does not give me any output from perl. When I run echo from the shell prompt it gives me output. Can you explain this behavior?
#!usr/bin/perl
$\="\n";
$out = `ls`;
print $out;
$out=`echo $PATH`;
print $out;
Please note that while the technically correct answer to your question is the $ interpolation, you should also note that you should not treat Perl like a shell script and call external commands via backticks instead of using Perl built-in or library functions designed for the purpose:
$out = join("\n", glob("*")); # same as `ls`
$out = $ENV{PATH}; # same as `echo $PATH`
This has several significant advantages:
speed (no call to system)
portability
More security (no shell attack vector)
Most built ins cover proper error handling for you better than your own system call implementation
Nearly always a better, cleaner, shorter and easier to read/maintain code
Backticks interpolate like double quotes, so you need to escape the $.
$out=`echo \$PATH`;
$PATH is shell variable, from perl you should use it as perl variable $ENV{PATH}
Still try to read some basic docs too, like perldoc perlintro. No need for executing echo at all.
Perl is interpolating $PATH in the backticks as a Perl variable, and you've not set a $PATH anywhere in your script, so the command is coming out as
$out = `echo `
which is basically a null-op. Try
$out = `echo \$PATH`
instead, which would force Perl to ignore the $ and pass it intact to the shell.
You need to escape $ in $PATH because the backticks operator interpolates any variables.
$out=`echo \$PATH`;
You could also use qx// with single quotes. From perldoc perlop:
Using single-quote as a delimiter
protects the command from Perl's
double-quote interpolation, passing it
on to the shell instead:
$perl_info = qx(ps $$); # that's Perl's $$
$shell_info = qx'ps $$'; # that's the new shell's $$
Others have already explained the reason - variables inside backticks are interpolated, so your echo $PATH is actually becoming echo since there's no $PATH variable declared.
However, always put use strict; at the top of every Perl script you write.
Had you done so, Perl would have told you what was happening, e.g.:
Global symbol "$PATH" requires explicit package name at myscript.pl line 9
To stop variables being interpolated, either escape them (e.g. \$PATH), or, more cleanly, use e.g. qx'echo $PATH'.
Also, as others have pointed out, calling echo $PATH makes no real-world sense; if you're trying to get the contents of the PATH environment variable, just use $ENV{PATH} - however, you may have just been using it as a simple reduced demonstration case.
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($command, #arguments);
For example:
system("sh", "script.sh", "--help" );
system("sh script.sh --help");
System will execute the $command with
#arguments and return to your script when finished. You may check $!
for certain errors passed to the OS by the external application. Read
the documentation for system for the nuances of how various
invocations are slightly different.
2. Using exec
This is very similar to the use of system, but it will
terminate your script upon execution. Again, read the documentation
for exec for more.
3. Using backticks or qx//
my $output = `script.sh --option`;
my $output = qx/script.sh --option/;
The backtick operator and it's equivalent qx//, excute the command and options inside the operator and return that commands output to STDOUT when it finishes.
There are also ways to run external applications through creative use of open, but this is advanced use; read the documentation for more.
From Perl HowTo, the most common ways to execute external commands from Perl are:
my $files = `ls -la` — captures the output of the command in $files
system "touch ~/foo" — if you don't want to capture the command's output
exec "vim ~/foo" — if you don't want to return to the script after executing the command
open(my $file, '|-', "grep foo"); print $file "foo\nbar" — if you want to pipe input into the command
Examples
`ls -l`;
system("ls -l");
exec("ls -l");
Look at the open function in Perl - especially the variants using a '|' (pipe) in the arguments. Done correctly, you'll get a file handle that you can use to read the output of the command. The back tick operators also do this.
You might also want to review whether Perl has access to the C functions that the command itself uses. For example, for ls -a, you could use the opendir function, and then read the file names with the readdir function, and finally close the directory with (surprise) the closedir function. This has a number of benefits - precision probably being more important than speed. Using these functions, you can get the correct data even if the file names contain odd characters like newline.
As you become more experienced with using Perl, you'll find that there are fewer and fewer occasions when you need to run shell commands. For example, one way to get a list of files is to use Perl's built-in glob function. If you want the list in sorted order you could combine it with the built-in sort function. If you want details about each file, you can use the stat function. Here's an example:
#!/usr/bin/perl
use strict;
use warnings;
foreach my $file ( sort glob('/home/grant/*') ) {
my($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks)
= stat($file);
printf("%-40s %8u bytes\n", $file, $size);
}
There are a lot of ways you can call a shell command from a Perl script, such as:
back tick
ls which captures the output and gives back to you.
system
system('ls');
open
Refer #17 here: Perl programming tips
You might want to look into open2 and open3 in case you need bidirectional communication.
I have been using system and qq to run linux programs inside perl. And it has worked well.
#!/usr/bin/perl # A hashbang line in perl
use strict; # It can save you a lot of time and headache
use warnings; # It helps you find typing mistakes
# my keyword in Perl declares the listed variable
my $adduser = '/usr/sbin/adduser';
my $edquota = '/usr/sbin/edquota';
my $chage = '/usr/bin/chage';
my $quota = '/usr/bin/quota';
my $nomeinteiro;
my $username;
my $home;
# system() function executes a system shell command
# qq() can be used in place of double quotes
system qq($adduser --home $home --gecos "$fullname" $username);
system qq($edquota -p john $username);
system qq($chage -E \$(date -d +180days +%Y-%m-%d) $username);
system qq($chage -l $username);
system qq($quota -s $username);
I find a lot of Perl one-liners online. Sometimes I want to convert these one-liners into a script, because otherwise I'll forget the syntax of the one-liner.
For example, I'm using the following command (from nagios.com):
tail -f /var/log/nagios/nagios.log | perl -pe 's/(\d+)/localtime($1)/e'
I'd to replace it with something like this:
tail -f /var/log/nagios/nagios.log | ~/bin/nagiostime.pl
However, I can't figure out the best way to quickly throw this stuff into a script. Does anyone have a quick way to throw these one-liners into a Bash or Perl script?
You can convert any Perl one-liner into a full script by passing it through the B::Deparse compiler backend that generates Perl source code:
perl -MO=Deparse -pe 's/(\d+)/localtime($1)/e'
outputs:
LINE: while (defined($_ = <ARGV>)) {
s/(\d+)/localtime($1);/e;
}
continue {
print $_;
}
The advantage of this approach over decoding the command line flags manually is that this is exactly the way Perl interprets your script, so there is no guesswork. B::Deparse is a core module, so there is nothing to install.
Take a look at perlrun:
-p
causes Perl to assume the following loop around your program, which makes it iterate over filename arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for some reason, Perl warns you about it, and moves on to the next file. Note that the lines are printed automatically. An error occurring during printing is treated as fatal. To suppress printing use the -n switch. A -p overrides a -n switch.
BEGIN and END blocks may be used to capture control before or after the implicit loop, just as in awk.
So, simply take this chunk of code, insertyour code at the "# your program goes here" line, and viola, your script is ready!
Thus, it would be:
#!/usr/bin/perl -w
use strict; # or use 5.012 if you've got newer perls
while (<>) {
s/(\d+)/localtime($1)/e
} continue {
print or die "-p destination: $!\n";
}
That one's really easy to store in a script!
#! /usr/bin/perl -p
s/(\d+)/localtime($1)/e
The -e option introduces Perl code to be executed—which you might think of as a script on the command line—so drop it and stick the code in the body. Leave -p in the shebang (#!) line.
In general, it's safest to stick to at most one "clump" of options in the shebang line. If you need more, you could always throw their equivalents inside a BEGIN {} block.
Don't forget chmod +x ~/bin/nagiostime.pl
You could get a little fancier and embed the tail part too:
#! /usr/bin/perl -p
BEGIN {
die "Usage: $0 [ nagios-log ]\n" if #ARGV > 1;
my $log = #ARGV ? shift : "/var/log/nagios/nagios.log";
#ARGV = ("tail -f '$log' |");
}
s/(\d+)/localtime($1)/e
This works because the code written for you by -p uses Perl's "magic" (2-argument) open that processes pipes specially.
With no arguments, it transforms nagios.log, but you can also specify a different log file, e.g.,
$ ~/bin/nagiostime.pl /tmp/other-nagios.log
Robert has the "real" answer above, but it's not very practical. The -p switch does a bit of magic, and other options have even more magic (e.g. check out the logic behind the -i flag). In practice, I'd simply just make a bash alias/function to wrap around the oneliner, rather than convert it to a script.
Alternatively, here's your oneliner as a script: :)
#!/usr/bin/bash
# takes any number of arguments: the filenames to pipe to the perl filter
tail -f $# | perl -pe 's/(\d+)/localtime($1)/e'
There are some good answers here if you want to keep the one-liner-turned-script around and possibly even expand upon it, but the simplest thing that could possibly work is just:
#!/usr/bin/perl -p
s/(\d+)/localtime($1)/e
Perl will recognize parameters on the hashbang line of the script, so instead of writing out the loop in full, you can just continue to do the implicit loop with -p.
But writing the loop explicitly and using -w and "use strict;" are good if plan to use it as a starting point for writing a longer script.
#!/usr/bin/env perl
while(<>) {
s/(\d+)/localtime($1)/e;
print;
}
The while loop and the print is what -p does automatically for you.