[bash] Pass all variables from one shell script to another?

Lets say I have a shell / bash script named test.sh with:

#!/bin/bash

TESTVARIABLE=hellohelloheloo
./test2.sh

My test2.sh looks like this:

#!/bin/bash

echo ${TESTVARIABLE}

This does not work. I do not want to pass all variables as parameters since imho this is overkill.

Is there a different way?

Fatal Error gave a straightforward possibility: source your second script! if you're worried that this second script may alter some of your precious variables, you can always source it in a subshell:

( . ./test2.sh )

The parentheses will make the source happen in a subshell, so that the parent shell will not see the modifications test2.sh could perform.

There's another possibility that should definitely be referenced here: use set -a.

From the POSIX set reference:

-a: When this option is on, the export attribute shall be set for each variable to which an assignment is performed; see the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.21, Variable Assignment. If the assignment precedes a utility name in a command, the export attribute shall not persist in the current execution environment after the utility completes, with the exception that preceding one of the special built-in utilities causes the export attribute to persist after the built-in has completed. If the assignment does not precede a utility name in the command, or if the assignment is a result of the operation of the getopts or read utilities, the export attribute shall persist until the variable is unset.

From the Bash Manual:

-a: Mark variables and function which are modified or created for export to the environment of subsequent commands.

So in your case:

set -a
TESTVARIABLE=hellohelloheloo
# ...
# Here put all the variables that will be marked for export
# and that will be available from within test2 (and all other commands).
# If test2 modifies the variables, the modifications will never be
# seen in the present script!
set +a

./test2.sh

 # Here, even if test2 modifies TESTVARIABLE, you'll still have
 # TESTVARIABLE=hellohelloheloo

Observe that the specs only specify that with set -a the variable is marked for export. That is:

set -a
a=b
set +a
a=c
bash -c 'echo "$a"'

will echo c and not an empty line nor b (that is, set +a doesn't unmark for export, nor does it “save” the value of the assignment only for the exported environment). This is, of course, the most natural behavior.

Conclusion: using set -a/set +a can be less tedious than exporting manually all the variables. It is superior to sourcing the second script, as it will work for any command, not only the ones written in the same shell language.

In Bash if you export the variable within a subshell, using parentheses as shown, you avoid leaking the exported variables:

#!/bin/bash

TESTVARIABLE=hellohelloheloo
(
export TESTVARIABLE    
source ./test2.sh
)

The advantage here is that after you run the script from the command line, you won't see a $TESTVARIABLE leaked into your environment:

$ ./test.sh
hellohelloheloo
$ echo $TESTVARIABLE
                            #empty! no leak
$

Adding to the answer of Fatal Error, There is one more way to pass the variables to another shell script.

The above suggested solution have some drawbacks:

1. using Export : It will cause the variable to be present out of their scope which is not a good design practice.
2. using Source : It may cause name collisions or accidental overwriting of a predefined variable in some other shell script file which have sourced another file.

There is another simple solution avaiable for us to use. Considering the example posted by you,

test.sh

#!/bin/bash

TESTVARIABLE=hellohelloheloo
./test2.sh "$TESTVARIABLE"

test2.sh

#!/bin/bash

echo $1

output

hellohelloheloo

Also it is important to note that "" are necessary if we pass multiword strings. Taking one more example

master.sh

#!/bin/bash
echo in master.sh
var1="hello world"
sh slave1.sh $var1
sh slave2.sh "$var1"
echo back to master

slave1.sh

#!/bin/bash
echo in slave1.sh
echo value :$1

slave2.sh

#!/bin/bash
echo in slave2.sh
echo value : $1

output

in master.sh
in slave1.sh
value :"hello
in slave2.sh
value :"hello world"

It happens because of the reasons aptly described in this link

There's actually an easier way than exporting and unsetting or sourcing again (at least in bash, as long as you're ok with passing the environment variables manually):

let a.sh be

#!/bin/bash
secret="winkle my tinkle"
echo Yo, lemme tell you \"$secret\", b.sh!
Message=$secret ./b.sh

and b.sh be

#!/bin/bash
echo I heard \"$Message\", yo

Observed output is

[rob@Archie test]$ ./a.sh
Yo, lemme tell you "winkle my tinkle", b.sh!
I heard "winkle my tinkle", yo

The magic lies in the last line of a.sh, where Message, for only the duration of the invocation of ./b.sh, is set to the value of secret from a.sh. Basically, it's a little like named parameters/arguments. More than that, though, it even works for variables like $DISPLAY, which controls which X Server an application starts in.

Remember, the length of the list of environment variables is not infinite. On my system with a relatively vanilla kernel, xargs --show-limits tells me the maximum size of the arguments buffer is 2094486 bytes. Theoretically, you're using shell scripts wrong if your data is any larger than that (pipes, anyone?)

Another option is using eval. This is only suitable if the strings are trusted. The first script can echo the variable assignments:

echo "VAR=myvalue"

Then:

eval $(./first.sh) ./second.sh

This approach is of particular interest when the second script you want to set environment variables for is not in bash and you also don't want to export the variables, perhaps because they are sensitive and you don't want them to persist.

Another way, which is a little bit easier for me is to use named pipes. Named pipes provided a way to synchronize and sending messages between different processes.

A.bash:

#!/bin/bash
msg="The Message"
echo $msg > A.pipe

B.bash:

#!/bin/bash
msg=`cat ./A.pipe`
echo "message from A : $msg"

Usage:

$ mkfifo A.pipe #You have to create it once
$ ./A.bash & ./B.bash # you have to run your scripts at the same time

B.bash will wait for message and as soon as A.bash sends the message, B.bash will continue its work.