How to slice an array in Bash

Question

Looking the  Array  section in the bash 1  man page  I didn t find a way to slice an array   So I came up with this overly complicated function      bin bash     brief  slice a bash array    arg1   output-name    arg2   input-name    args   seq args   ---------------------------------------------- function slice        local output  1    local input  2    shift 2    local indexes   seq         local -i i    local tmp   for i in  indexes                   do echo    eval echo       input  i                       done      local IFS    n     eval  output      tmp        Used like this     A   foo bar  a  b c  42     slice B A 1 2   echo    B 0       bar   echo    B 1       a  b c   Is there a better way to do this

User · Accepted Answer

See the Parameter Expansion section in the Bash man page. A[@] returns the contents of the array, :1:2 takes a slice of length 2, starting at index 1.

A=( foo bar "a  b c" 42 )
B=("${A[@]:1:2}")
C=("${A[@]:1}")       # slice to the end of the array
echo "${B[@]}"        # bar a  b c
echo "${B[1]}"        # a  b c
echo "${C[@]}"        # bar a  b c 42
echo "${C[@]: -2:2}"  # a  b c 42 # The space before the - is necesssary

Note that the fact that "a b c" is one array element (and that it contains an extra space) is preserved.

User · Answer

Array slicing like in Python  From the rebash library    array slice         local   doc         Returns a slice of an array  similar to Python        From the Python documentation      One way to remember how slices work is to think of the indices as pointing     between elements  with the left edge of the first character numbered 0      Then the right edge of the last element of an array of length n has     index n  for example               --- --- --- --- --- ---        0   1   2   3   4   5        --- --- --- --- --- ---      0   1   2   3   4   5   6     -6  -5  -4  -3  -2  -1               gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice 1 -2    a           1 2 3      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice 0 1    a           0      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    -z    array slice 1 1    a           amp  amp  echo empty     empty      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    -z    array slice 2 1    a           amp  amp  echo empty     empty      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    -z    array slice -2 -3    a           amp  amp  echo empty     empty      gt  gt  gt    -z    array slice -2 -2    a           amp  amp  echo empty     empty      Slice indices have useful defaults  an omitted first index defaults to     zero  an omitted second index defaults to the size of the string being     sliced       gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    from the beginning to position 2  excluded       gt  gt  gt  echo   array slice 0 2    a            gt  gt  gt  echo   array slice  2    a           0 1     0 1       gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    from position 3  included  to the end      gt  gt  gt  echo   array slice 3     a         a            gt  gt  gt  echo   array slice 3     a           3 4 5     3 4 5       gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt    from the second-last  included  to the end      gt  gt  gt  echo   array slice -2     a         a            gt  gt  gt  echo   array slice -2     a           4 5     4 5       gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice -4 -2    a           2 3      If no range is given  it works like normal array indices       gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice -1    a           5      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice -2    a           4      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice 0    a           0      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  echo   array slice 1    a           1      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  array slice 6    a       echo        1      gt  gt  gt  local a  0 1 2 3 4 5       gt  gt  gt  array slice -7    a       echo        1           local start end array length length     if     1            then         IFS      read -r start end  lt  lt  lt   1          shift         array length                defaults           -z   end     amp  amp  end  array length           -z   start     amp  amp  start 0            start  lt  0     amp  amp  let  start    array length   start                end  lt  0     amp  amp  let  end    array length   end         else         start   1          shift         array length                 start  lt  0     amp  amp  let  start    array length   start             let  end    start   1         fi     let  length    end - start            start  lt  0     amp  amp  return 1       check bounds        length  lt  0     amp  amp  return 1        start  lt  0     amp  amp  return 1        start  gt   array length     amp  amp  return 1       parameters start with  1  so add 1 to  start     let  start    start   1         echo        start  length     alias array slice  array slice

User · Answer

There is also a convenient shortcut to get all elements of the array starting with specified index  For example    A    1   would be the  tail  of the array  that is the array without its first element   version 4 7 1 A     version          echo    A           4 7 1 B      A    1     echo    B           7 1

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