How can I join elements of an array in Bash

Question

If I have an array like this in Bash   FOO   a b c     How do I join the elements with commas   For example  producing a b c

User · Answer

If you build the array in a loop  here is a simple way   arr    for x in   some cmd   do    arr    x   done arr -1    arr -1     echo   arr

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Surprisingly my solution is not yet given    This is the simplest way for me  It doesn t need a function   IFS   eval  joined    foo         Note  This solution was observed to work well in non-POSIX mode  In POSIX mode  the elements are still joined properly  but IFS   becomes permanent

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My attempt     array  one two  three four  five    echo    array 0    printf   SEP  s     array    1     one SEP two SEP three four SEP five

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Perhaps I m missing something obvious  since I m a newb to the whole bash zsh thing  but it looks to me like you don t need to use printf at all  Nor does it get really ugly to do without   join       separator  1   arr      arr   arr 2    throw away separator and following space   arr   arr     separator      At least  it has worked for me thus far without issue   For instance  join      sh  which  let s say I m in my   directory  outputs utilities sh play sh foobar sh  Good enough for me   EDIT  This is basically Nil Geisweiller s answer  but generalized into a function

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In case the elements you want to join is not an array just a space separated string  you can do something like this   foo  aa bb cc dd  bar  for i in  foo  do printf     s    i  done  bar   bar 1  echo  bar      aa   bb   cc   dd    for example  my use case is that some strings are passed in my shell script and I need to use this to run on a SQL query     my script  aa bb cc dd    In my script  I need to do  SELECT   FROM table WHERE name IN   aa   bb   cc   dd    Then above command will be useful

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Use perl for multicharacter separators   function join      perl -e   s   shift  ARGV  print join  s   ARGV              join      a b c   a  b  c   Or in one line   perl -le  print join shift   ARGV         1 2 3 1  2  3

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printf solution that accept separators of any length  based on  doesn t matters answer      bin bash foo   foo bar   foo baz   bar baz    sep       can be of any length bar   printf    sep  s     foo       bar   bar    sep    echo  bar

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Yet another solution      bin bash foo   foo bar   foo baz   bar baz   bar   printf    s     foo       bar   bar 1   echo  bar   Edit  same but for multi-character variable length separator      bin bash separator         e g  constructing regex  pray it does not contain  s foo   foo bar   foo baz   bar baz   regex     printf    separator  s     foo         regex    regex    separator      remove leading separator echo    regex     Prints  foo bar   foo baz   bar baz

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s   IFS   eval  echo    FOO

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foo  a  b c  d    bar   IFS     echo    foo         echo   bar  a b c d

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Right now I m using   TO IGNORE       E201   Whitespace after         E301   Expected N blank lines  found M     E303   Too many blank lines  pep8 gets confused by comments    ARGS  --ignore  echo   TO IGNORE       tr             Which works  but  in the general case  will break horribly if array elements have a space in them    For those interested  this is a wrapper script around pep8 py

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liststr    for item in list do     liststr  item  liststr done LEN  expr length  liststr  LEN  expr  LEN - 1  liststr   liststr 0  LEN    This takes care of the extra comma at the end also  I am no bash expert  Just my 2c  since this is more elementary and understandable

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Here s a single liner that is a bit weird but works well for multi-character delimiters and supports any value  including containing spaces or anything   ar  abc  quot foo bar quot  456  delim  quot     quot  printf  quot  s n delim n quot   quot   ar     quot    head -n-1   paste -sd     This would show in the console as abc   foo bar   456  Note  Notice how some solutions use printf with   ar     and some with   ar      The ones with   use the printf feature that supports multiple arguments by repeating the format template  The ones with   should not be used  They do not actually need printfand rely on manipulating the field separator and bash s word expansion  These would work just as well with echo  cat  etc  - these solutions likely use printf because the author doesn t really understand what they are doing

User · Answer

Here s one that most POSIX compatible shells support   join by           Usage   join by      a b c d     local arg arr    sep   1      shift     for arg in       do         if   0 -lt     arr         then             arr      sep            fi         arr      arg       break     done     printf   s     arr

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I would echo the array as a string  then transform the spaces into line feeds  and then use paste to join everything in one line like so   tr       n   lt  lt  lt    FOO    paste -sd   -  Results   a b c  This seems to be the quickest and cleanest to me

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Many  if not most  of these solutions rely on arcane syntax  brain-busting regex tricks  or calls to external executables  I would like to propose a simple  bash-only solution that is very easy to understand  and only slightly sub-optimal  performance-wise  join by            Argument  1 is the separator  It can be multi-character        Argument  2  3  and so on  are the elements to be joined        Usage  join by  quot    quot   quot   array     quot      local SEPARATOR  quot  1 quot      shift      local F 0     for x in  quot    quot      do         if    F -eq 1            then             echo -n  quot  SEPARATOR quot          else             F 1         fi         echo -n  quot  x quot      done     echo    Example    a   1  quot 2 2 quot  3     join by  quot    quot   quot   a     quot  1  2 2  3     I d like to point out that any solution that uses  usr bin   or  usr bin printf is inherently slower than my solution  since I use 100  pure bash  As an example of its performance  Here s a demo where I create an array with 1 000 000 random integers  then join them all with a comma  and time it    eval   echo -n  quot a   quot   x 0   while    x -lt 1000000     do echo -n  quot   RANDOM quot    x    x 1    done  echo  quot    quot     time join by     a      gt  dev null real    0m8 590s user    0m8 591s sys     0m0 000s

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With re-use of  doesn t matters  solution  but with a one statement by avoiding the    1  substition and need of an intermediary variable   echo   printf   s      LIST        cut -d     -f 1-   LIST         printf has  The format string is reused as often as necessary to satisfy the arguments   in its man pages  so that the concatenations of the strings is documented  Then the trick is to use the LIST length to chop the last sperator  since cut will retain only the lenght of LIST as fields count

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Maybe  e g    SAVE IFS   IFS  IFS     FOOJOIN    FOO      IFS   SAVE IFS   echo   FOOJOIN

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Shorter version of top answer   joinStrings     local a       3     printf   s    2  a       1        Usage   joinStrings   myDelimiter     myArray

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Here s a 100  pure Bash function that does the job   join            1 is return variable name        2 is sep        3    are the elements to join     local retname  1 sep  2 ret  3     shift 3    shift             printf -v   retname    s    ret       sep       Look     a   one two  three three  four five     join joineda   and      a        echo   joineda  one and two and three three and four and five   join joinedb randomsep  only one element    echo   joinedb  only one element   join joinedc randomsep   echo   joinedc     a      stuff with nnewlines n    and trailing newlines n n      join joineda   a sep with nnewlines n     a        echo   joineda   stuff with newlines a sep with newlines and trailing newlines       This preserves even the trailing newlines  and doesn t need a subshell to get the result of the function  If you don t like the printf -v  why wouldn t you like it   and passing a variable name  you can of course use a global variable for the returned string   join            1 is sep        2    are the elements to join       return is in global variable join ret     local sep  1 IFS      join ret  2     shift 2    shift             join ret          sep

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Using variable indirection to refer directly to an array also works   Named references can also be used  but they only became available in 4 3   The advantage of using this form of a function is that you can have the separator optional  defaults to the first character of default IFS  which is a space  perhaps make it an empty string if you like   and it avoids expanding values twice  first when passed as parameters  and second as      inside the function    This solution also doesn t require the user to call the function inside a command substitution - which summons a subshell  to get a joined version of a string assigned to another variable   function join by ref               local   r  1      s   2-         printf -v         s         s        r                    s      array  1 2 3 4   join by ref array echo         Prints  1 2 3 4    join by ref array   s  echo         Prints  1 s2 s3 s4    join by ref  invalid     s    Bash 4 4 shows  invalid      bad substitution   echo         Prints nothing but newline    Feel free to use a more comfortable name for the function   This works from 3 1 to 5 0-alpha   As observed  variable indirection doesn t only work with variables but with other parameters as well      A parameter is an entity that stores values   It can be a name  a   number  or one of the special characters listed below under Special   Parameters   A variable is a parameter denoted by a name    Arrays and array elements are also parameters  entities that store value   and references to arrays are technically references to parameters as well   And much like the special parameter    array    also makes a valid reference   Altered or selective forms of expansion  like substring expansion  that deviate reference from the parameter itself no longer work   Update  In the release version of Bash 5 0  variable indirection is already called indirect expansion and its behavior is already explicitly documented in the manual      If the first character of parameter is an exclamation point      and   parameter is not a  nameref   it introduces  a level of indirection     Bash uses the value formed by expanding the rest of parameter as the   new parameter  this is then expanded and that value is used in the   rest of the expansion   rather than  the  expansion  of  the original   parameter   This is known as indirect expansion    Taking note that in the documentation of   parameter   parameter is referred to as  a shell parameter as described  in  PARAMETERS or an array reference    And in the documentation of arrays  it is mentioned that  Any element of an array may be referenced using   name subscript       This makes   r    an array reference   Join by arguments version  See my comment in Riccardo Galli s answer

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awk -v sep    BEGIN ORS OFS    for i 1 i lt ARGC i    print ARGV i  ARGC-i-1 sep          arr        or    a  1  a b  3    b   IFS     echo    a         echo  b 1 a b 3

User · Answer

This approach takes care of spaces within the values  but requires a loop      bin bash  FOO   a b c   BAR     for index in    FOO     do     BAR   BAR   FOO  index    done echo   BAR 1

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x      arr             This is the shortest way to do it   Example   arr  1 2 3 4 5  x      arr            echo  x    output  1 2 3 4 5

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Thanks  gniourf gniourf for detailed comments on my combination of best worlds so far  Sorry for posting code not thoroughly designed and tested  Here is a better try      join with separator join ws     local d  1 s  2  shift 2  amp  amp  printf  s   s       d        This beauty by conception is    still  100  pure bash   thanks for explicitly pointing out that printf is a builtin as well  I wasn t aware about this before       works with multi-character delimiters more compact and more complete and this time carefully thought over and long-term stress-tested with random substrings from shell scripts amongst others  covering use of shell special characters or control characters or no characters in both separator and   or parameters  and edge cases  and corner cases and other quibbles like no arguments at all  That doesn t guarantee there is no more bug  but it will be a little harder challenge to find one  BTW  even the currently top voted answers and related suffer from such things like that -e bug       Additional examples     join ws    a b c abc   join ws      1 7  A  C  1A 1B 1C 7A 7B 7C   join ws -e -e -e   join ws    033 F     n n n   1   2   3      n n n n  3  2  1    join ws

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set a  b c  d    history -p        paste -sd  a b c d

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Using no external commands     FOO   a b c         initialize the array   BAR   FOO           create a space delimited string from array   BAZ   BAR           use parameter expansion to substitute spaces with comma   echo  BAZ a b c   Warning  it assumes elements don t have whitespaces

User · Answer

Perhaps late for the party  but this works for me   function joinArray       local delimiter    1     local output    2     for param in     3   do     output    output   delimiter   param     done    echo    output

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Combine best of all worlds so far with following idea     join with separator join ws      local IFS   local s         1    echo    s   1 1 1         This little masterpiece is   100  pure bash   parameter expansion with IFS temporarily unset  no external calls  no printf       compact  complete and flawless   works with single- and multi-character limiters  works with limiters containing white space  line breaks and other shell special characters  works with empty delimiter   efficient   no subshell  no array copy   simple and stupid and  to a certain degree  beautiful and instructive as well   Examples     join ws   a b c a b c   join ws    a b c abc   join ws    n  a b c a b c   join ws        A B C A    B    C

User · Answer

A 100  pure Bash function that supports multi-character delimiters is  function join by   local d  1  shift  local f  1  shift  printf  s  quot  f quot   quot        d  quot      For example  join by   a b c  a b c join by       a b c  a   b   c join by       a b c  a   b   c join by    s   a b c  a  s b  s c join by    n  a b c  a lt newline gt b lt newline gt c join by - a b c  a-b-c join by     a b c  a b c join by  -n   -e   -E   -n   -e-n-E-n-n join by     join by   a  a  The code above is based on the ideas by  gniourf gniourf   AdamKatz  and  MattCowell  Alternatively  a simpler function that supports only a single character delimiter  would be  function join by   local IFS  quot  1 quot   shift  echo  quot    quot      For example  join by   a  quot b c quot  d  a b c d join by   var local tmp  var local tmp join by    quot   FOO     quot   a b c  This solution is based on Pascal Pilz s original suggestion  A detailed explanation of the solutions proposed here can be found in  quot How to join   array elements in a bash script quot   an article by meleu at dev to

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This isn t all too different from existing solutions  but it avoids using a separate function  doesn t modify IFS in the parent shell and is all in a single line   arr  a b c  printf   s n     IFS    printf   s     arr          resulting in  a b c   Limitation  the separator can t be longer than one character

[arrays] How can I join elements of an array in Bash?

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