Passing arrays as parameters in bash

Question

How can I pass an array as parameter to a bash function  Note  After not finding an answer here on Stack Overflow  I posted my somewhat crude solution myself  It allows for only one array being passed  and it being the last element of the parameter list  Actually  it is not passing the array at all  but a list of its elements  which are re-assembled into an array by called function    but it worked for me  If someone knows a better way  feel free to add it here

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You can pass multiple arrays as arguments using something like this   takes ary as arg         declare -a argAry1      1        echo    argAry1           declare -a argAry2      2        echo    argAry2        try with local arys           array variables could have local scope     local descTable            sli4-iread           sli4-iwrite           sli3-iread           sli3-iwrite            local optsTable            --msix  --iread           --msix  --iwrite           --msi   --iread           --msi   --iwrite            takes ary as arg descTable    optsTable      try with local arys   will echo   sli4-iread sli4-iwrite sli3-iread sli3-iwrite   --msix  --iread --msix  --iwrite --msi   --iread --msi   --iwrite   Edit notes   from comments below    descTable and optsTable are passed as names and are expanded in the function  Thus no   is needed when given as parameters  Note that this still works even with descTable etc being defined with local  because locals are visible to the functions they call  The   in    1  expands the arg 1 variable  declare -a just makes the indexed array explicit  it is not strictly necessary

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The basic problem here is that the bash developer s  that designed implemented arrays really screwed the pooch   They decided that   array  was just short hand for   array 0    which was a bad mistake  Especially when you consider that   array 0   has no meaning and evaluates to the empty string if the array type is associative   Assigning an array takes the form array  value1     valueN  where value has the syntax  subscript  string  thereby assigning a value directly to a particular index in the array   This makes it so there can be two types of arrays  numerically indexed and hash indexed  called associative arrays in bash parlance    It also makes it so that you can create sparse numerically indexed arrays   Leaving off the  subscript   part is short hand for a numerically indexed array  starting with the ordinal index of 0 and incrementing with each new value in the assignment statement   Therefore    array  should evaluate to the entire array  indexes and all   It should evaluate to the inverse of the assignment statement   Any third year CS major should know that   In that case  this code would work exactly as you might expect it to   declare -A foo bar foo   bar    Then  passing arrays by value to functions and assigning one array to another would work as the rest of the shell syntax dictates   But because they didn t do this right  the assignment operator   doesn t work for arrays  and arrays can t be passed by value to functions or to subshells or output in general  echo   array   without code to chew through it all   So  if it had been done right  then the following example would show how the usefulness of arrays in bash could be substantially better   simple  first one second 2 third 3  echo   simple    the resulting output should be    first one second 2 third 3    Then  arrays could use the assignment operator  and be passed by value to functions and even other shell scripts   Easily stored by outputting to a file  and easily loaded from a file into a script   declare -A foo read foo  lt file   Alas  we have been let down by an otherwise superlative bash development team   As such  to pass an array to a function  there is really only one option  and that is to use the nameref feature   function funky         local -n ARR      ARR  1     echo  indexes     ARR          echo  values    ARR         declare -A HASH  HASH   foo  bar  zoom  fast  funky HASH   notice that I m just passing the word  HASH  to the function   will result in the following output   indexes  foo zoom values  bar fast   Since this is passing by reference  you can also assign to the array in the function   Yes  the array being referenced has to have a global scope  but that shouldn t be too big a deal  considering that this is shell scripting   To pass an associative or sparse indexed array by value to a function requires throwing all the indexes and the values onto the argument list  not too useful if it s a large array  as single strings like this   funky     array         array        and then writing a bunch of code inside the function to reassemble the array

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Commenting on Ken Bertelson solution and answering Jan Hettich    How it works  the takes ary as arg descTable    optsTable    line in try with local arys   function sends    This is actually creates a copy of the descTable and optsTable arrays which are accessible to the takes ary as arg function   takes ary as arg   function receives descTable    and optsTable    as strings  that means  1    descTable    and  2    optsTable     in the beginning of takes ary as arg   function it uses    parameter  syntax  which is called indirect reference or sometimes double referenced  this means that instead of using  1 s value  we use the value of the expanded value of  1  example   baba booba variable baba echo   variable    baba echo    variable    booba   likewise for  2  putting this in argAry1      1    creates argAry1 as an array  the brackets following    with the expanded descTable     just like writing there argAry1     descTable       directly   the declare there is not required    N B   It is worth mentioning that array initialization using this bracket form initializes the new array according to the IFS or Internal Field Separator which is by default tab  newline and space  in that case  since it used     notation each element is seen by itself as if he was quoted  contrary to        My reservation with it  In BASH  local variable scope is the current function and every child function called from it  this translates to the fact that takes ary as arg   function  sees  those descTable    and optsTable    arrays  thus it is working  see above explanation    Being that case  why not directly look at those variables themselves  It is just like writing there   argAry1     descTable         See above explanation  which just copies descTable    array s values according to the current IFS   In summary     This is passing  in essence  nothing by value - as usual    I also want to emphasize Dennis Williamson comment above  sparse arrays  arrays without all the keys defines - with  holes  in them  will not work as expected - we would loose the keys and  condense  the array   That being said   I do see the value for generalization  functions thus can get the arrays  or copies  without knowing the names    for   copies   this technique is good enough  just need to keep aware  that the indices  keys  are gone  for real copies  we can use an eval for the keys  for example   eval local keys       1      and then a loop using them to create a copy  Note  here   is not used it s previous indirect double evaluation  but rather in array context it returns the array indices  keys     and  of course  if we were to pass descTable and optsTable strings  without       we could use the array itself  as in by reference  with eval  for a generic function that accepts arrays

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function aecho     set   1  2     echo     1       Example    foo  dog cat bird     aecho foo 1 cat

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With a few tricks you can actually pass named parameters to functions  along with arrays   The method I developed allows you to access parameters passed to a function like this   testPassingParams           var hello     l 4  array anArrayWithFourElements     l 2  array anotherArrayWithTwo      var anotherSingle      reference table     references only work in bash  gt  4 3      params anArrayOfVariedSize      test   hello      1   amp  amp  echo correct           test    anArrayWithFourElements 0        2   amp  amp  echo correct     test    anArrayWithFourElements 1        3   amp  amp  echo correct     test    anArrayWithFourElements 2        4   amp  amp  echo correct       etc              test    anotherArrayWithTwo 0        6   amp  amp  echo correct     test    anotherArrayWithTwo 1        7   amp  amp  echo correct           test   anotherSingle      8   amp  amp  echo correct           test    table test       works      table inside   adding a new value              I m using   just in this example      test    anArrayOfVariedSize             10    amp  amp  echo correct    fourElements   a1 a2  a3 with spaces  a4   twoElements   b1 b2   declare -A assocArray assocArray test   works   testPassingParams  first     fourElements         twoElements       single with spaces  assocArray  and more       even more      test    assocArray inside       adding a new value    In other words  not only you can call your parameters by their names  which makes up for a more readable core   you can actually pass arrays  and references to variables - this feature works only in bash 4 3 though   Plus  the mapped variables are all in the local scope  just as  1  and others     The code that makes this work is pretty light and works both in bash 3 and bash 4  these are the only versions I ve tested it with   If you re interested in more tricks like this that make developing with bash much nicer and easier  you can take a look at my Bash Infinity Framework  the code below was developed for that purpose   Function AssignParamLocally         local commandWithArgs    1       local command    commandWithArgs 0         shift      if      command      trap       command      l         command       type           then         paramNo  -1         return 0     fi      if      command      local         then         assignNormalCodeStarted true     fi      local varDeclaration    commandWithArgs 1        if     varDeclaration     -n         then         varDeclaration    commandWithArgs 2        fi     local varName    varDeclaration              var value is only important if making an object later on from it     local varValue    varDeclaration           if      -z  assignVarType        then         local previousParamNo   expr  paramNo - 1           if      assignVarType      array             then               passing array              execute   assignVarName           previousParamNo  assignArrLength                   eval   execute              paramNo    expr  assignArrLength - 1               unset assignArrLength         elif      assignVarType      params             then             execute   assignVarName           previousParamNo                   eval   execute          elif      assignVarType      reference             then             execute   assignVarName      previousParamNo                eval   execute          elif      -z     previousParamNo              then             execute   assignVarName      previousParamNo                eval   execute          fi     fi      assignVarType     capture type      assignVarName   varName      assignArrLength     capture arrLength     Function CaptureParams           capture type    type        capture arrLength   l     alias  trapAssign  Function CaptureParams  trap  declare -i   paramNo  1    Function AssignParamLocally     BASH COMMAND                 assignNormalCodeStarted   true     amp  amp  trap - DEBUG  amp  amp  unset assignVarType  amp  amp  unset assignVarName  amp  amp  unset assignNormalCodeStarted  amp  amp  unset paramNo  DEBUG    alias  param   trapAssign local  alias  reference   type reference  trapAssign local -n  alias  var   type var  param  alias  params   type params  param  alias  array   type array  param

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Just to add to the accepted answer  as I found it doesn t work well if the array contents are someting like   RUN COMMANDS      command1 param1    paramN     command2 param1    paramN      In this case  each member of the array gets split  so the array the function sees is equivalent to   RUN COMMANDS        command1       param1                command2              To get this case to work  the way I found is to pass the variable name to the function  then use eval   function          eval  COMMANDS         1               for COMMAND in    COMMANDS       do         echo  COMMAND     done    function RUN COMMANDS   Just my 2

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This one works even with spaces   format   t 2s -  s n   function doAction     local array          for    i   0   i  lt     local array       i          do       printf    format    i    local array  i      done   echo -n  Choose      option      read -n1 option   echo   local array option     return     the call  doAction    tools

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My short answer is   x000D   x000D  function display two array   x000D      local arr1  1 x000D      local arr2  2 x000D      for i in  arr1 x000D      do x000D          arrary1   i  x000D      done x000D       x000D      for i in  arr2 x000D      do x000D          arrary2   i  x000D      done x000D    x000D   x000D  test array  1 2 3 4 5  x000D  test array2  7 8 9 10 11  x000D   x000D  display two array    test array         test array2      x000D   x000D   x000D   It should be noticed that the   test array     and   test array2     should be surrounded by     otherwise you ll fail

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As ugly as it is  here is a workaround that works as long as you aren t passing an array explicitly  but a variable corresponding to an array    function passarray         eval array internally     echo      1                access array now via array internally     echo    array internally                  array  0 1 2 3 4 5  passarray array   echo s  0 1 2 3 4 5  as expected   I m sure someone can come up with a clearner implementation of the idea  but I ve found this to be a better solution than passing an array as   array      and then accessing it internally using array inside         This becomes complicated when there are other positional getopts parameters  In these cases  I ve had to first determine and then remove the parameters not associated with the array using some combination of shift and array element removal    A purist perspective likely views this approach as a violation of the language  but pragmatically speaking  this approach has saved me a whole lot of grief  On a related topic  I also use eval to assign an internally constructed array to a variable named according to a parameter target varname I pass to the function   eval  target varname      array inside        Hope this helps someone

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An easy way to pass several arrays as parameter is to use a character-separated string  You can call your script like this     myScript sh  value1 value2 value3   somethingElse   value4 value5   anotherOne    Then  you can extract it in your code like this   myArray  1 IFS     read -a myArray  lt  lt  lt    myArray   myOtherArray  3 IFS     read -a myOtherArray  lt  lt  lt    myOtherArray    This way  you can actually pass multiple arrays as parameters and it doesn t have to be the last parameters

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DevSolar s answer has one point I don t understand  maybe he has a specific reason to do so  but I can t think of one   He sets the array from the positional parameters element by element  iterative   An easier approuch would be  called function               do everything like shown by DevSolar            now get a copy of the positional parameters   local array

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Note  This is the somewhat crude solution I posted myself  after not finding an answer here on Stack Overflow  It allows for only one array being passed  and it being the last element of the parameter list  Actually  it is not passing the array at all  but a list of its elements  which are re-assembled into an array by called function    but it worked for me  Somewhat later Ken posted his solution  but I kept mine here for  quot historic quot  reference  calling function         variable  quot a quot      array    quot x quot    quot y quot    quot z quot        called function  quot   variable  quot   quot   array     quot     called function         local variable  quot   1  quot      shift     local array   quot      quot

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Requirement  Function to find a string in an array  This is a slight simplification of DevSolar s solution in that it uses the arguments passed rather than copying them   myarray   foobar   foxbat    function isInArray       local item  1   shift   for one in     do     if    one    item    then       return 0     found     fi   done   return 1         not found    var  foobar  if isInArray  var   myarray      then   echo   var found in array  else   echo   var not found in array  fi

[arrays] Passing arrays as parameters in bash

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Examples related to arrays

Examples related to bash