Pass all variables from one shell script to another

Question

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

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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  gt  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  amp    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

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You have basically two options    Make the variable an environment variable  export TESTVARIABLE  before executing the 2nd script  Source the 2nd script  i e    test2 sh and it will run in the same shell  This would let you share more complex variables like arrays easily  but also means that the other script could modify variables in the source shell    UPDATE   To use export to set an environment variable  you can either use an existing variable   A 10       export A   This ought to work in both bash and sh   bash also allows it to be combined like so   export A 10   This also works in my sh  which happens to be bash  you can use echo  SHELL to check    But I don t believe that that s guaranteed to work in all sh  so best to play it safe and separate them   Any variable you export in this way will be visible in scripts you execute  for example   a sh      bin sh  MESSAGE  hello  export MESSAGE   b sh   b sh      bin sh  echo  The message is   MESSAGE    Then       a sh The message is  hello   The fact that these are both shell scripts is also just incidental   Environment variables can be passed to any process you execute  for example if we used python instead it might look like   a sh      bin sh  MESSAGE  hello  export MESSAGE   b py   b py      usr bin python  import os  print  The message is    os environ  MESSAGE     Sourcing   Instead we could source like this   a sh      bin sh  MESSAGE  hello       b sh   b sh      bin sh  echo  The message is   MESSAGE    Then       a sh The message is  hello   This more or less  imports  the contents of b sh directly and executes it in the same shell  Notice that we didn t have to export the variable to access it  This implicitly shares all the variables you have  as well as allows the other script to add delete modify variables in the shell   Of course  in this model both your scripts should be the same language  sh or bash   To give an example how we could pass messages back and forth   a sh      bin sh  MESSAGE  hello       b sh  echo   A  The message is   MESSAGE    b sh      bin sh  echo   B  The message is   MESSAGE   MESSAGE  goodbye    Then       a sh  B  The message is  hello  A  The message is  goodbye   This works equally well in bash   It also makes it easy to share more complex data which you could not express as an environment variable  at least without some heavy lifting on your part   like arrays or associative arrays

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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

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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

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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    using Export   It will cause the variable to be present out of their scope which is not a good design practice  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

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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

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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

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

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