While the man for env on Linux seems to indicate that you can set new environment variables before executing a command. Unfortunately, when I set new variables in a file's shebang on Linux systems, the file never executes.
#!/usr/bin/env VAR1=foo bash
echo $VAR1
When I execute this file on a CentOS or Ubuntu machine, it just sits there.
$ ./shell-env.sh
<nothing happens>
What I find particularly bizarre is this works perfectly fine on OS X with BSD env.
$ ./shell-env.sh
foo
$
Is this just a difference between BSD env and Linux env? Why do the man pages for Linux seem to say it should work the same way as on BSD?
P.S. My use case here is to override the PATH variable, so I can try to find a ruby on the system but that's not on the PATH.
Thank you in advance!
There's a way to manipulate the environment before executing a Ruby script, without using a wrapper script of some kind, but it's not pretty:
#!/bin/bash
export FOO=bar
exec ruby -x "$0" "$#"
#!ruby
puts ENV['FOO']
This is usually reserved for esoteric situations where you need to manipulate e.g. PATH or LD_LIBRARY_PATH before executing the program, and it needs to be self-contained for some reason. It works for Perl and possibly others too!
Related
I have been working on a node script that does the installation of external dependencies and was wondering if its possible to set the PATH variable using Node.
For example, If I want to install Go using script, I can execute command brew install Go and this works but when I do export GOPATH=$PATH, this is never set.
I also tried using process.env but this also does not work. Also my assumption with process is that it must run in a sandbox. So it will not update/ set anything outside.
So the question is, can I do this? If yes, how?
It is not possible in any programming language. At least on Unix (BSD, MacOS, Illumos etc.) and Linux, I'm not sure about Windows.
As a security feature, Unix processes are designed such that they cannot touch the environment of their parent's process. Only the parent process can influence the environment of their children.
When you are on a command line you are running a shell program (either Bash or Korn Shell or TCSH or Fish etc.). When you execute something on the command line such as a node.js script or Google Chrome or Minecraft these programs will be the children to your shell program. On Unix and Linux these child programs inherit their parent's environment.
That is why you can export environment (global) variables and your programs can access them. However, this relationship is one-way and it was designed that way on purpose.
You may notice that in shell scripts you can "save" commands to set environment variables in a file. For example in Bash you sometimes see people do this:
# variables.sh
export HELLO "World"
However, this will not work if you execute the script as a script:
$ bash variables.sh
$ echo $HELLO
<--------------------- nothing is displayed here
the variable is not exported
You sometimes see people do this instead:
$ . variables.sh
$ echo $HELLO
World
And you may wonder how that works. Well.. in some shell languages the dot command imports the script instead of executing the script as a separate process. Think of it like import or require() in javascript.
Of course, Bash does not understand javascript syntax. It also does not understand C++ or Java or Ruby or PHP. It only understands Bash syntax.
So the longer answer is it is not possible in any programming language except for the language of the shell you are using (eg. if you are using Fish you need to write a script in Fish syntax or if you are using Ksh you need to write a script in Korn syntax).
I develop a Tcl/Tk script tool in Linux. In order to run the tool, every time I need to set the environment variable like this in shell:
setenv LD_LIBRARY_PATH /opt/lsf/9.1/linux2.6-glibc2.3-x86_64/lib:/abc/software/new_2015/GE/tcl_tk/lib64:/abc/software/new_2015/GE/tcl_tk/lib64
and then use "wish" interpreter to launch my tool:
/abc/software/new2015/GE/tcl_tk/bin/wish mytool.tk
To make it a little easy to use, I want design a shell script "abc_wish" and put the above command inside:
#!/bin/sh
setenv LD_LIBRARY_PATH /opt/lsf/9.1/linux2.6-glibc2.3-x86_64/lib:/abc/software/new_2015/GE/tcl_tk/lib64:/abc/software/new_2015/GE/tcl_tk/lib64
wish="/abc/software/new2015/GE/tcl_tk/bin/wish"
exec $wish $#
And then I need just run:
./abc_wish mytool.tk
But error message shows that setenv command not found!I am totally new to such system issues, need some help about these stuffs. Hope I have shown the issue clearly.
setenv is a csh command, not a sh command. The equivalent in bash is export:
#!/bin/sh
export LD_LIBRARY_PATH=/opt/lsf/9.1/linux2.6-glibc2.3-x86_64/lib:/abc/software/new_2015/GE/tcl_tk/lib64:/abc/software/new_2015/GE/tcl_tk/lib64
exec wish "$#"
You should also put $# in quote, to ensure proper re-quoting of the expansion.
This question already has answers here:
How to Share ENV Variables Among Perl Scripts
(2 answers)
Closed 5 years ago.
I am trying to set an environment variable, LD_LIBRARY_PATH, through a Perl script in the following way:
I have created .profile under /root
.profile has an export command say:
export LD_LIBRARY_PATH=/
My Perl script is test.pl and it has:
#!/usr/bin/perl
system(". /root/.profile");
When I execute ./test.pl, LD_LIBRARY_PATH doesn't change.
What am I doing wrong?
Your current script doesn't even change an environment variable in the Perl script itself. Rather, it invokes a shell as a subprocess; that shell process executes . /root/.profile, which updates $LD_LIBRARY_PATH only in that shell process.
You can change an environment variable in a Perl script (more precisely, in the process running the Perl script) by updating %ENV:
$ENV{LD_LIBRARY_PATH} = '/'; # or some more reasonable value
As perldoc -v %ENV says:
%ENV The hash %ENV contains your current environment. Setting a value in "ENV" changes the environment for any child processes you subsequently "fork()" off.
But that probably still won't do what you want; it won't (and can't) affect the environment of the process that invokes the Perl script (your interactive shell), only the Perl process itself and anything it invokes.
I'll assume you want to update $LD_LIBRARY_PATH in your current interactive shell process. To do that, you can have you Perl script print a shell command that will update $LD_LIBRARY_PATH. Then, rather than simply running your Perl script, you can execute it and then evaluate its output. For example:
$ cat env.pl
#!/usr/bin/perl
use strict;
use warnings;
print "export LD_LIBRARY_PATH=/\n";
$ ./env.pl # just prints the command without executing it
export LD_LIBRARY_PATH=/
$ eval $(./env.pl) # executes the command in the current shell
$ echo $LD_LIBRARY_PATH
/
$
This assumes that your current shell is bash or something similar.
Another option: After modifying %ENV, your Perl script can invoke another command, even a new interactive shell. The new process will inherit its environment from the Perl script. This can be a bit cumbersome, though; for example, if the new process is an interactive shell, it won't inherit unexported variables or history from the parent shell.
(One note, not directly related to your question: The fact that you're messing with /root/.profile implies that you're doing things as root (superuser). This can be dangerous. Use the root account (either by logging into it or via sudo only for things that actually need root privileges. For anything else, use a personal user account.
To change the environment in a Perl script, assign to the %ENV hash:
$ENV{'LD_LIBRARY_PATH'} = '/';
If you want to write a program that's used by a shell to change its environment, the way this is generally done is to have the script write shell commands to stdout. The shell then executes this with command substitution and uses eval to execute the resulting commands:
Perl script:
#!/usr/bin/perl
print 'LD_LIBRARY_PATH=\n';
Shell script:
eval "$(/path/to/perlscript)"
For examples of commands that work like this, see tset and ssh-agent.
system starts a new process, and changing the environment there won't affect the environment in the process of your script (usually—there are generally os-dependent means of changing other processes' environments).
The environment in a perl program is associated with %ENV, which is kind of like (it isn't actually) a tied hash to the environment: changing it will change the environment. Thus:
$ENV{LD_LIBRARY_PATH} = '/';
This can now be done with the Env::Modify module:
use Env::Modify 'source';
source("/root/.profile");
... env settings of .profile are now available to Perl ...
You can't do it.
This is from the Perl FAQ:
In the strictest sense, it can't be done--the script executes as a different process from the shell it was started from. Changes to a process are not reflected in its parent--only in any children created after the change. There is shell magic that may allow you to fake it by eval()ing the script's output in your shell; check out the comp.unix.questions FAQ for details.
I am trying to use setenv variable in my makefile but when I execute my make file it gives setenv: command not found.
How can I use it?
Actually I wanted to run a shell script which sets multiple environment variables.
Since the list is very huge I dont have an option except to use the scripts. I cant set them manually like
abcd:= /xx/yy/zz
Please suggest.
P.S. the same command
setenv xxx yyy works very well in shell
it just fails when I use in makefile directly or makefile with a script having this command.
'
Why do not you use export command ?
Running the script to set the environment variable will not work as the shell run a separate process & will not reflect in your current shell. You will need to source the shell script. You can use source or . based on your shell. Following is a sample for your reference where setvar.sh sets a variable & print.sh prints it; in the Makefile (mkfile) setvar.sh is being sourced using .
$ cat setvar.sh
export TEST=ABC
$ cat print.sh
echo $TEST
$ cat mkfile
test:
. ./setvar.sh && ./print.sh
.SILENT:test
$ make -f mkfile
ABC
You can also include I guess for example,
$ cat mkfile2
include setvar.sh
test:
./print.sh
.SILENT:test
$ make -f mkfile2
ABC
Hope this helps!
Look at
make -e
and Communicating Variables to a Sub-make
I think setenv is not a builtin to the sh shell. If you are using GNU Make that is the default shell used. In your situation you probably want to use a different shell, like bash. You do this by setting the SHELL variable in the makefile to what you want like:
SHELL := /usr/bin/bash
For more information checkout this section of the GNU Make manual. It details the different behavior of the SHELL variable and how it is, or isn't inherited from the shell make is invoked from on different platforms.
EDIT: I agree with the implication of the other posters that you are probably not setting enviroment variables the way you think you should be and would not be using the setenv command at. I am just responding to your original question. To learn about variables in make files checkout these other sections in the GNU Make manual.
export MY_VAR := "/package/your_path"
I have a script whose content simply exports a variable in linux.
export LD_LIBRARY_PATH=....
I want to run this script in my Perl script so whoever is running my Perl script will have their LD_LIBRARY_PATH set. Can i just do this in the beginning of my Perl script:
#!/usr/bin/perl -w
system(". /myfolder1/myfolder2/myScript.sh");
#!/bin/sh
. /myfolder1/myfolder2/myScript.sh
exec perl -wxS "$0" "$#"
#!/usr/bin/perl -w
# .. the rest of your script as normal
When you run this, it will first be executed by /bin/sh, which is capable of loading myScript.sh into the local environment. sh then execs Perl, which is told to continue from the following line.
This won't work. To change the environment inside your Perl script (and to change the environment that will be passed on to commands run from inside your Perl script), change the %ENV variable.
$ENV{"LD_LIBRARY_PATH"} = ... ;
This won't work. There is no way for a subshell to manipulate the environment of the parent process.
But you could make your script echo the string you want to set as LD_LIBRARY_PATH and then from within your Perl script you could do something like that:
$ENV{LD_LIBRARY_PATH} = `path/to/your/script.sh`;
Of course, a bit of error checking might also be a good idea.
No. Your environment changes made in a child cannot affect the parent. This means running a script will not affect perl. Also perl will not affect the shell from which it was called. You can edit the environment inside perl by changing the special variable %ENV. If there's some kind of unreproducible calculation done in that script, maybe the script should just echo the setting and perl can pick that up on STDOUT and use it.
I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible?
Unix In the strictest sense, it can't be done -- the script executes
as a different process from the shell
it was started from. Changes to a
process are not reflected in its
parent, only in its own children
created after the change.
I had a similar problem a few years ago and whipped up a little module, Env::Sourced, that should do the trick.
use Env::Sourced qw(/myfolder1/myfolder2/myScript.sh);
...
Another option (other than making the changes directly in Perl's %ENV) is to make the changes you want a Perl module, so that you can say:
use MyEnvironment;
and have it modify your environment in all your scripts. It would make it simple to make changes after the fact that will not require editing every script.
The module itself will be simple, something like this:
package MyEnvironment;
$ENV{LD_LIBRARY_PATH} .= ":/some/path/you/want/appended";
# Any other changes you want here.
1;
That won't work. An (unpleasant) alternative might be to replace /usr/bin/perl with a shell script that first executes your script and then executes the perl executable.
This can't be done in the way you're trying to do this.
It either needs a wrapper shell script that sets LD_LIBRARY_PATH and then calls your perl script, or any user executing the script needs to have LD_LIBRARY_PATH set correctly in the first place.
If doing the latter, then this can be managed globally by editing /etc/profile and /etc/cshrc (for ksh, sh, bash, csh and tcsh) shells. You can then test for the value of LD_LIBRARY_PATH in your script and if not set/set incorrectly then print a friendly message to the user. Alternatively individual users can set this in their local .profile/.cshrc files.
Note: you haven't given any information about the environment or useres that might run this, so there's also the possibility that users may set LD_LIBRARY_PATH to something they need. If you do check LD_LIBRARY_PATH for a "good" value in your script, then keep in mind that several paths may have been specified, so you will need to parse this environment variable properly.
If you can find the right place in your perl script, this works as in my example:
$ENV{"LD_LIBRARY_PATH"} = "/oracle/product/10g/lib";
And it didn't require me to call another script to set the env var.
The Env::Modify module addresses this issue, at least for POSIX-y platforms:
use Env::Modify 'source';
source("/myfolder1/myfolder2/myScript.sh");
... environment settings from myScript.sh are now available to Perl ...