I'm trying to make variables exits outside of a shell script without using source.
The variables are declared in shell script with
export varA=3
and I run the script with ./filename.sh
I want
echo $varA
in the terminal to return 3 (i.e. the value of varA). So extend the scope of the variable to outside of the script
To sum up: how do I make the variables inside a shell script exist outside.
Thank you in advance
You can run your script on this way:
. ./filename.sh
This mean when run it will not spawn new shell but run it in current. And variables you set in your script will be available in your shell. This is kind of "source" as mentioned in comments.
Related
I have a set of environment variables that need to be set on the basis of the arguments specified in the shell script.
But the problem is that those variables are already defined in the bash profile
FOR EXAMPLE:
bash_profile has a variable called "KARAN":
export KARAN=/config/1
Now on running the shell script, this is what it should do:
export KARAN=/config/2 (Changed the bash profile's KARAN value to 2)
Your question is not clear. If your script needs to set the env var to a specific value just do so using export VAR=val. What I think you're asking is how to have a script modify the environment of the current shell. And that is impossible without the cooperation of both shells. That is because environment vars are inherited by child processes. But a child process cannot directly modify the environment of its parent process (or some other random process for that matter). To do so the two processes must coordinate the exchange of data. This is typically done by using the source command if the child process is a shell script. Or by having the child process write a series of export statements to stdout and having the parent shell capture and execute those statements. For example, let's say I have a script named set_env that looks like this
#!/bin/sh
echo export KARAN=/config_2
echo export VAR2=val2
The current shell would then do
eval $(set_env)
Note, however, eval is dangerous. I prefer to do this which is slightly safer:
set_env | source /dev/stdin
That, however, only works in shells like ksh and zsh. Due to how bash handles pipelines the source is actually executed in a child shell and therefore the vars won't be set in the current shell.
You can create a new Profile with all the new definitions. and then call the line below on top of your shell script. Similarly, you can create as many profiles as you want and use it.
source bash_profile_new
my project, which uses mapreduce without hadoop, is composed of two files:
bash.sh and mapreduce.py.
I would like to use environment variables to communicate the information between bash.sh and mapreduce.py.
Within bash.sh I use export myvariable and on mapreduce.py, I use os.environ ['myvariable'].
I would like to edit myvariable within mapreduce.py and print the result via bash.sh. I tried to execute this istruction: os.environ ['myvariable'] = 'hello', but on bash.sh 'myvariable' is empty. Do you have any suggestions?
You can't do it from python, but some clever bash tricks can do
something similar. The basic reasoning is this: environment variables
exist in a per-process memory space. When a new process is created
with fork() it inherits its parent's environment variables. When you
set an environment variable in your shell (e.g. bash) like this:
/why-cant-environmental-variables-set-in-python-persist
So you can only make available to Bash script if the bash script is called inside python process space. A simple example can be
bash script
#!/bin/bash
echo "var from python is $myvariable"
python script
import os
os.environ ['myvariable'] = 'hello'
print(os.environ['myvariable'])
# all environment varaibles will be availbe to bash script in this case
os.system('sh ./ab.sh')
This is the way that you can try. Otherwise, no way to set it and make it available to bash script.
Setting an environment variable sets it only for the current process
and any child processes it launches. So using os.system will set it
only for the shell that is running to execute the command you
provided. When that command finishes, the shell goes away, and so does
the environment variable. Setting it using os.putenv or os.environ has
a similar effect; the environment variables are set for the Python
process and any children of it.
ENV via python
You can also try vice versa as you mention in question
Here is sequence
First set in bash script
call python script from bash ( based on argument to avoid loop)
update ENV in python
call bash again from python, if you call outside it will vanish.
bash script
#!/bin/bash
export myvariable="hellobash"
echo "myvariable form bash $myvariable"
if [ ! -z $1 ]; then
./py.py
else
echo "myvariable after updated from python $myvariable"
fi
Call bash script outside from python with the argument like myscript.sh bash, without argument in python myscript.sh
#!/usr/bin/python
import os
print("myvar form python",os.environ['myvariable'])
os.environ ['myvariable'] = 'hello'
print("myvar form python after update",os.environ['myvariable'])
os.system('sh ./ab.sh')
I did the following from a bash shell.
export myPath="/home/user/dir"
Then I verified the value of this by 'echo'ing this value from both shell and a inside a bash script. Both worked fine.
Then I tried setting the value of this variable from inside a script like this.
myPath="/home/user/newdir"
and tried printing this variable from shell. I thought the variable will hold the updated value, but it was showing the old value.
How can I update the value from a script? I am looking to do it without using source if possible.
To make the variables persist after the script finishes, you have to run it using the source command:
When a script is run using source it runs within the existing shell, any variables created or modified by the script will remain available after the script completes. In contrast if the script is run just as filename, then a separate subshell (with a completely separate set of variables) would be spawned to run the script.
I have a simple bash script:
#!/bin/bash
JAVA_HOME=/usr
EC2_HOME=~/ec2-api
echo $EC2_HOME
export PATH=$PATH:$EC2_HOME/bin
I run the script like so
$ ./ec2
/Users/user/ec2-api
The script runs and produces the correct output.
However, when I now try to access the EC2_HOME variable, I get nothing out:
$ echo $EC2_HOME
I get a blank string back. What am I doing wrong?
Do either of the following instead:
source ec2
or
. ec2
(note the . notation is just a shortcut for source)
Explanation:
This is because ./ec2 actually spawns a subshell from your current shell to execute the script, and subshells cannot affect the environment of the parent shell from which it spawned.
Thus, EC2_HOME does get set to /Users/user/ec2-api correctly in the subshell (and similarly the PATH environment variable is updated and exported correctly in the subshell as well), but those changes won't propagate back to your parent shell.
Using source runs the script directly in the current shell without spawning a subshell, so the changes made will persist.
(A note on export: export is used to tell new shells spawned from the current shell to use the variables exported from the current shell. So for any variables you would only use in the current shell, they need not be exported.)
A shell script can never modify the environment of their parent.
To fix your problem, you can use the dot (.) command:
$ . ./ec2
and that should work. In cshell, it would be
% source ./ec2
To learn more about shells and scripts, my best resource is by far Unix power tools.
I have some proxy settings that I only occasionally want to turn on, so I don't want to put them in my ~/.bash_profile. I tried putting them directly in ~/bin/set_proxy_env.sh, adding ~/bin to my PATH, and chmod +xing the script but though the script runs, the variables don't stick in my shell. Does anyone know how to get them to stick around for the rest of the shell session?
Use one of:
source <file>
. <file>
In the script use
export varname=value
and also execute the script with:
source set_proxy_env.sh.
The export keyword ensures the variable is marked for automatic inclusion in the environment of subsequently executed commands. Using source to execute a script starts it with the present shell instead of launching a temporary one for the script.
Did you try this:
. ~/bin/set_proxy_env.sh
Running it by itself opens a separate subshell (I think) and sets the variable there. But then the binding is lost after exiting back into your shell. The dot at the front tells it to run it within the same shell.
Also, don't forget to export the variables you need like so: export MYVAR=value