I am not sure whether the title is really make sense to this problem. My problem is simple, I want to write a perl script to change my current directory and hope the result can be kept after calling the perl script. The script looks like this:
if ($#ARGV != 0) {
print "usage: mycd <dir symbol>";
exit -1;
}
my $dn = shift #ARGV;
if ($dn eq "kite") {
my $cl = `cd ./private`;
print $cl."\n";
}
else {
print "unknown directory symbol";
exit -1;
}
However, my current directory doesn't change after calling the script. What is the reason? How can I resolve it?
No, the Perl script will be run in a subprocess so it will not be able to affect the environment of the process that called it.
There are various tricks you can use such as sourcing shell scripts (in the context of the current shell rather than a sub-process), or using bash functions and aliases, but they won't work here.
How Perl can execute a command in the same shell with it?
Unless you have a very atypical shell, shells can only receive commands via STDIN, via its command line, and possibly via a command evaluation builtin.
The first two are out unless the Perl script is the parent of the shell, but you could use the third one indirectly as in the following example.
script.pl:
#!/usr/bin/perl
print "chdir 'private'\n";
bash script:
echo "$PWD" # /some/dir
eval "$( script.pl )"
echo "$PWD" # /some/dir/private
Of course, if you use bash, you could hide the details in a shell function.
mycd () {
eval "$( mycd.pl "$#" )"
}
Allowing you use to use
mycd
or even
mycd foo
Related
I am writing a simple Perl program to test a shell script for changing directory. But it doesn't work.
This is my code :
$result = `cd/`;
print $result;
It works fine when I use
$result =`dir`;
If you need to change the cwd directory in your script, then you should use Perl's built-in chdir function.
perldoc -f chdir
cd (by default) doesn't output anything, so you're assigning an empty string to your $result variable.
If you want to output the (full) path of the directory you changed to, simply append && pwd inside the backticks:
$result = `cd / && pwd`;
Note that `...` creates a child process for running the shell with the specified command, so whatever environment changes you perform there - including changing the directory - do NOT affect the Perl script itself.
In other words: you're NOT changing the Perl script's current directory with your shell command.
If your intent is:
to simply test whether the shell command you enclose in `...` succeeds or not, use, the system() function instead; e.g.:
system('cd /') == 0 || die "Command failed";
to capture the output from the shell command, presume it to be a directory path and change the Perl script's working directory to it:
$result = `cd / && pwd` || die "Command failed.";
chomp $result; # trim trailing newline
# Change Perl script's working dir.
chdir $result || die "Could not change to $result.";
To affect the current working directory of the perl process, use the chdir() function.
I would like to use a small script to do some cosmetic work to the output of my gcc.
So I use this command:
mygcc foo.c 2>&1 | myscript.pl
Basically my script does things like this:
$error = 0;
while(<>)
{
s/^"(.*)"\s*,\s*line\s*(\d+)\s*:\s*(cc\d+)\s*:/colored("[$3]", 'bold red').colored(" $1", 'red').":".colored("$2", 'yellow')/ge;
s/ \^/colored(" ^", 'yellow')/e;
s/(error:.*$)/colored($1, 'red')/ge;
s/(warning.*$)/colored($1, 'yellow')/ge;
print;
$error = -1;
}
Unfortunately the exit code from gcc is not correctly propagated through the pipe. What I need to do is to get the exit code from gcc and write it back from my script.
Without this, make won't correctly stop the build process in case of an error.
How can I achieve this?
Try using a sub shell:
( mygcc foo.c; echo "gcc returned $?" ) |& myscript.pl
The ( cmd ) construct is used to launch cmd in a sub-shell. Your current shell will fork itself, and the commands will be executed by the child shell. It's an easy way to run multiple commands and have the output fed to a pipe.
The $? variable is the exit status of the last command.
The cmd1 |& cmd1 construct is equivalent to cmd1 2>&1 | cmd2
Take a look at this. You can then use the %ENV variable to access the gcc return status and return that value from your perl script.
I have a file with 4 perl commands ,
I want to open the file from the tcl and execute each perl command.
TCL script
runcmds $file
proc runcmds {file} {
set fileid [open $file "r"]
set options [read $fileid]
close $fileid
set options [split $options "\n"] #saperating each commad with new line
foreach line $options {
exec perl $line
}
}
when executing the above script
I am getting the error as "can't open the perl script /../../ : No Such file or directory " Use -S to search $PATH for it.
tl;dr: You were missing -e, causing your script to be interpreted as a filename.
To run a perl command from inside Tcl:
proc perl {script args} {
exec perl -e $script {*}$args
# or in 8.4: eval [list perl -e $script] $args
}
Then you can do:
puts [perl {
print "Hello "
print "World\n"
}]
That's right, an arbitrary perl script inside Tcl. You can even pass in other arguments as necessary; access from perl via #ARGV. (You'll need to add other options like -p explicitly.)
Note that this can pass whole scripts; you don't need to split them up (and probably shouldn't; you can do lots with one-liners but they tend to be awful to maintain and there's no technical reason to require it).
Perl Code
`. /home/chronicles/logon.sh `;
print "DATA : $ENV{ID}\n";
In logon.sh , we are exporting the variable "ID" (sourcing of shell script).
Manual run
$> . /home/chronicles/logon.sh
$> echo $LOG
While I am running in terminal manually (not from script). I am getting the output. (But not working from the script)
I followed this post :
How to export a shell variable within a Perl script?
But didnt solve the problem.
Note
I am not allowed to change "logon.sh" script.
The script inside the backticks is executed in a child process. While environment variables are inherited from parent processes, the parent can't access the environment of child processes.
However, you could return the contents of the child environment variable and put it into a Perl variable like
use strict; use warnings; use feature 'say';
my $var = `ID=42; echo \$ID`;
chomp $var;
say "DATA: $var";
output:
DATA: 42
Here an example shell session:
$ cat test_script
echo foo
export test_var=42
$ perl -E'my $cmd = q(test_var=0; . test_script >/dev/null; echo $test_var); my $var = qx($cmd); chomp $var; say "DATA: $var"'
DATA: 42
The normal output is redirected into /dev/null, so only the echo $test_var shows.
It won't work.
An environment variable can't be inherited from a child process.
The environment variable can be updated in your "manual run" is because it's in the same "bash" process.
Source command is just to run every command in login.sh under current shell.
More info you can refer to: can we source a shell script in perl script
You could do something like:
#/usr/bin/perl
use strict;
use warnings;
chomp(my #values = `. myscript.sh; env`);
foreach my $value (#values) {
my ($k, $v) = split /=/, $value;
$ENV{$k} = $v;
}
foreach my $key (keys %ENV) {
print "$key => $ENV{$key}\n";
}
Well, I've find a solution, that sound nice for me: This seem robust, as this use widely tested mechanism to bind shell environment to perl (running perl) and robust library to export them in a perl variable syntax for re-injecting in root perl session.
The line export COLOR tty was usefull to ask my bash to export newer variables... This seem work fine.
#!/usr/bin/perl -w
my $perldumpenv='perl -MData::Dumper -e '."'".
'\$Data::Dumper::Terse=1;print Dumper(\%ENV);'."'";
eval '%ENV=('.$1.')' if `bash -c "
. ./home/chronicles/logon.sh;
export COLOR tty ID;
$perldumpenv"`
=~ /^\s*\{(.*)\}\s*$/mxs;
# map { printf "%-30s::%s\n",$_,$ENV{$_} } keys %ENV;
printf "%s\n", $ENV{'ID'};
Anyway, if you don't have access to logon.sh, you have to trust it before running such a solution.
Old...
There is my first post... for history purpose, don't look further.
The only way is to parse result command, while asking command to dump environ:
my #lines=split("\n",`. /home/chronicles/logon.sh;set`);
map { $ENV{$1}=$2 if /^([^ =])=(.*)$/; } #lines;
This can now be done with the Env::Modify module
use Env::Modify 'source';
source("/home/chronicles/logon.sh");
... environment setup in logon.sh is now available to Perl ...
Your Perl process is the parent of the shell process, so it won't inherit environment variables from it. Inheritance works the other way, from parent to child.
But when you run the script with backticks, as shown, the standard output of the script is returned to the Perl script. So, either modify the shell script to end with the echo $LOG statement you show, or create a new shell script that runs the login.sh and then has echo $LOG. Your Perl script would then be:
my $value = `./myscript.sh`;
print $value;
I have a shell script, with a list of shell variables, which is executed before entering a programming environment.
I want to use a Perl script to enter the programming environment:
system("environment_defaults.sh");
system("obe");
But when I enter the environment the variables are not set.
When you call your second command, it's not done in the environment you modified in the first command. In fact, there is no environment remaining from the first command, because the shell used to invoke "environment_defaults.sh" has already exited.
To keep the context of the first command in the second, invoke them in the same shell:
system("source environment_defaults.sh && obe");
Note that you need to invoke the shell script with source in order to perform its actions in the current shell, rather than invoking a new shell to execute them.
Alternatively, modify your environment at the beginning of every shell (e.g. with .bash_profile, if using bash), or make your environment variable changes in perl itself:
$ENV{FOO} = "hello";
system('echo $FOO');
Different sh -c processes will be called and environment variables are isolated within these.
Also doesn't calling environment_defaults.sh also make another sh process within what these variables will be set to in isolation?
Or start the Perl script with these environment variables exported and these will be set for all its child processes.
Each process gets its own environment, and each time you call "system" it runs a new process. So, what you are doing won't work. You'll have to run both commands in a single process.
Be aware, however, that after your Perl script exists, any environment variables it sets won't be available to you at the command line, because your Perl script is also a process with its own environment.
(UPDATE: Oh, this is not exactly what you asked for, but it might be useful for someone.)
If GDB is installed, you can set/modify parent shell variables with the following hack (non-strict style is used for clarity):
#!/usr/bin/perl
# export.pl
use File::Temp qw( tempfile );
%vars = (
a => 3,
b => 'pigs'
);
$ppid = getppid;
my #putvars = map { "call putenv (\"$_=$vars{$_}\")" } keys %vars;
$" = "\n";
$cmds = <<EOF;
attach $ppid
#putvars
detach
quit
EOF
($tmpfh, $tmpfn) = tempfile( UNLINK => 1 );
print $tmpfh $cmds;
`gdb -x $tmpfn`
Test:
$ echo "$a $b"
$ ./export.pl
$ echo "$a $b"
3 pigs
This can now be done with the Env::Modify module
use Env::Modify 'source'; # or use Env::Modify qw(source system);
source("environment_defaults.sh");
... environment from environment_defaults.sh is now available
... to Perl and to the following 'system' call
system("obe");