I have a script which I run and after it's run it has some information that I need to pass to the next script to run.
The Unix/DOS commands are like so:
perl -x -s param_send.pl
perl -x -s param_receive.pl
param_send.pl is:
# Send param
my $send_var = "This is a variable in param_send.pl...\n";
$ARGV[0] = $send_var;
print "Argument: $ARGV[0]\n";
param_receive.pl is:
# Receive param
my $receive_var = $ARGV[0];
print "Parameter received: $receive_var";
But nothing is printed. I know I am doing it wrong but from the tutorials I can't figure out how to pass a parameter from one script to the next!
You can use a pipe character on the command line to connect stdout from the first program to stdin on the second program, which you can then write to (using print) or read from (using the <> operator).
perl param_send.pl | perl param_receive.pl
If you want the output of the first command to be the arguments to the second command, you can use xargs:
perl param_send.pl | xargs perl param_receive.pl
The %ENV hash in Perl holds the environment variables such as PATH, USER, etc. Any modifications to these variables is reflected 'only' in the current process and any child process that it may spawn. The parent process (which happens to be the shell in this particular instance) does not reflect these changes so when the 'param_send.pl' script ends all changes are lost.
For e.g. if you were to do something like,
#!/usr/bin/perl
# param_send.pl
$ENV{'VAL'} = "Value to send to param_recv";
#!/usr/bin/perl
# param_recv.pl
print $ENV{'VAL'};
This wouldn't work since VAL is lost when param_send exits. One workaround is to call param_recv.pl from param_send.pl and pass the value as an environment variable or an argument,
#!/usr/bin/perl
# param_send.pl
$ENV{'VAL'} = "Value to send to param_recv";
system( $^X, "param_recv.pl");
OR
#!/usr/bin/perl
# param_send.pl
system( $^X, qw(param_recv.pl 'VAL') );
Other options include piping the output or you could check out this Perlmonks node for a more esoteric solution.
#ARGV is created at runtime and does not persist. So your second script will not be able to see the $ARGV[0] you assigned in the first script. As crashmstr points out you either need to execute the second script from the first using one of the many methods for doing so. For example:
my $send_var = "This is a variable in param_send.pl...\n";
`perl param_receive.pl $send_var`;
or use an environment variable using %ENV:
my $send_var = "This is a variable in param_send.pl...\n";
$ENV['send_var'] = $send_var;
For a more advanced solutions think about using sockets or IPC.
Related
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($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);
I am having some trouble of getting the argument passed in in the following script
echo "abc"|perl <<'EOF'
#how to get "abc". it seems not $ARGV[0] nor in <STDIN>
EOF
Thank you.
The precise command line you have there may be your problem, if that is what you're actually executing. What you are saying there is "put 'abc' on the standard input of the next thing in the pipeline. Now run a Perl script consisting of a single comment."
This will do nothing, because there's nothing executable in that Perl script. Try this:
echo "abc" | perl -e 'print <STDIN>'
If you have a short Perl script the -e option is the way to go.
Your example is not using argument, it's using standard input. You can read standard input with the I/O operators. If you actually mean that you want an argument like myscript.pl --arg then I would recommend using Getopt::Long.
You have not passed any argument to the Perl script.
You redirected the Perl script itself so it comes from standard input; that means that the piped output goes nowhere and cannot be seen by Perl.
Reconsider how you're invoking your script. Maybe:
perl script.pl "abc"
where script.pl is a file that contains the Perl script you used as a here-document. Or simply make that script executable (perhaps without the .pl suffix).
Your problem is that both the pipe and the here-document redirect the STDIN. And the here-document wins, so the perl process never sees the pipe; it gets the script on STDIN (and has read to EOF before running the script, so that will see STDIN at EOF).
Observe:
$ echo "abc" | perl <<'EOF'
print "[What have we here?]\n";
seek(STDIN, 0, 0);
print <STDIN>;
print "[Well, what do you know ...]\n";
EOF
[What have we here?]
print "[What have we here?]\n";
seek(STDIN, 0, 0);
print <STDIN>;
print "[Well, what do you know ...]\n";
[Well, what do you know ...]
$
Moral: Don't try to mix pipes and here-documents in the shell. :)
I have a perl script which takes 2 arguments as follows and calls appropriate function depending on the argument. I call this script from bash, but i want to call it from perl, is it possible?
/opt/sbin/script.pl --group="value1" --rule="value2";
Also the script exits with a return value that I would like to read.
The Perl equivalent of sh command
/opt/sbin/script.pl --group="value1" --rule="value2"
is
system('/opt/sbin/script.pl', '--group=value1', '--rule=value2');
You could also launch the command in a shell by using the following, though I'd avoid doing so:
system(q{/opt/sbin/script.pl --group="value1" --rule="value2"});
Just like you'd have to do in sh, you'll have to follow up with some error checking (whichever approach you took). You can do so by using use autodie qw( system );. Check the docs for how to do it "manually" if you want more flexibility.
If you want to capture the output:
$foo = `/opt/sbin/script.pl --group="value1" --rule="value2"`;
If you want to capture the exit status, but send script.pl's output to stdout:
$status = system "/opt/sbin/script.pl --group=value1 --rule=value2";
If you want to read its output like from a file:
open SCRIPT, "/opt/sbin/script.pl --group=value1 --rule=value2 |" or die $!;
while (<SCRIPT>) ...
Yes. You can use system, exec, or <backticks>.
The main difference between system and exec is that exec "executes a command and never returns.
Example of system:
system("perl", "foo.pl", "arg");
I use a Perl script to configure and spawn a compiled program, that needs a subshell configured a certain way, so I use $returncode = system("ulimit -s unlimited; sg ourgroup 'MyExecutable.exe'");
I want to capture and parse the STDOUT from that, but I need it forked, so that the output can be checked while the job is still running. This question comes close:
How can I send Perl output to a both STDOUT and a variable? The highest-rated answer describes a function called backtick() that creates a child process, captures STDOUT, and runs a command in it with exec().
But the calls I have require multiple lines to configure the shell. One solution would be to create a disposable shell script:
#disposable.sh
#!/bin/sh
ulimit -s unlimited
sg ourgroup 'MyExecutable.exe'
I could then get what I need either with backtick(disposable.sh) or open(PROCESS,'disposable.sh|').
But I'd really rather not make a scratch file for this. system() happily accepts multi-line command strings. How can I get exec() or open() to do the same?
If you want to use shell's power (that includes loops, variables, but also multiple command execution), you have to invoke the shell (open(..., 'xxx|') doesn't do that).
You can pass your shell script to the shell with the -c option of the shell (another possibility would be to pipe the commands to the shell, but that's more difficult IMHO).
That means calling the backtick function from the other answer like this:
backtick("sh", "-c", "ulimit -s unlimited; sg ourgroup 'MyExecutable.exe'");
The system tee with backticks will do this, no?
my $output = `(ulimit -s unlimited; sg ourgroup 'MyExecutable.exe') | tee /dev/tty`;
or modify Alnitak's backticks (so it does use a subshell)?
my $cmd = "ulimit -s unlimiited ; sg ourgroup 'MyExecutable.exe'";
my $pid = open(CMD, "($cmd) |");
my $output;
while (<CMD>) {
print STDOUT $_;
$output .= $_;
}
close CMD;
Expect should be used as you are interacting with your program: http://metacpan.org/pod/Expect
Assuming /bin/bash on your *nix matches something like bash-3.2$ the below program can be used to launch number of commands using $exp->send on bash console and output from each command can then be parsed for further actions.
#!/usr/bin/perl
use Expect;
my $command="/bin/bash";
my #parameters;
my $exp= new Expect;
$exp->raw_pty(1);
$exp->spawn($command);
$exp->expect(5, '-re', 'bash.*$');
$exp->send("who \n");
$exp->expect(10, '-re', 'bash.*$');
my #output = $exp->before();
print "Output of who command is #output \n";
$exp->send("ls -lt \n");
$exp->expect(10, '-re', 'bash.*$');
my #output = $exp->before();
print "Output of ls command is #output \n";
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($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);