Arrays (Bash): verschil tussen versies
Regel 175: | Regel 175: | ||
echo "Whole array: ${j[@]}" | echo "Whole array: ${j[@]}" | ||
echo "Item 5: ${j[5]}" | echo "Item 5: ${j[5]}" | ||
+ | </pre> | ||
+ | |||
+ | == Arithmatic with arrays == | ||
+ | |||
+ | This works, so no <code>(())</code> black magic today. At least, not here: | ||
+ | |||
+ | <pre> | ||
+ | i=5 | ||
+ | echo "Entry i (=5): ${j[$i]}" | ||
+ | echo "Entry i+1: ${j[$i+1]}" | ||
+ | echo "Entry 6: ${j[6]}" | ||
</pre> | </pre> | ||
Versie van 12 okt 2022 16:59
Beginnetje
#!/bin/bash a=(1 2 "Drie" 4 "Vijf") echo $a # Returns "1" - First item of the array echo $a[0] # Returns "1[0]" - The [0] part is treated as a literal echo ${a[0]} # Returns "1" echo ${a[@]} # Returns "1 2 3 4" - whole array
Nog een beginnetje:
a[0]="Nul" a[1]="Eén" echo $a # Toont alleen eerste element echo $a[0] # Output: Null[0] - Waarschijnlijk niet wat de bedoeling was echo ${a[1]} # OK
Multi-dimensional arrays
Bash ondersteunt geen multidimensionale arrays, maar je kunt een heel eind komen middels associative arrays
Associative arrays
Length of an array
E.g.:
Return all indices
${!j[@]}
returns all indices. This may not be what I expected. E.g.:
unset j mapfile -t j < <( wp post list --post_type=product --field=ID --posts_per_page=64 ) echo "Number of items: ${!j[@]}"
Output (some output removed):
Number of items: 0 1 2 3 ... 64 65
Something doesn't add up
Note that there are 64, 65 and/or 66 items, depending on how you ask:
unset j mapfile -t j < <( wp post list --post_type=product --field=ID --posts_per_page=64 ) echo "Whole array: ${j[@]}" # 64 IDs echo "Item 5: ${j[5]}" echo "All indices: ${!j[@]}" # 0 to 65 = 66 indices echo "Number of items: ${#j[@]}" # 66
Answer: The first two entries contain NULL. Maybe just some unfortunate null space that mapfile
couldn't avoid.
Loop through array
Dit werkt. Merk op dat $i
de waarde van de cel bevat, niet de index:
array=( one two three ) for i in "${array[@]}" do echo "$i" done
Loop through the index of an array
Rather than going through the entries of an array, let's loop through its index. Note that this is base 0:
array=( one two three ) for i in "${!array[@]}" do echo "Index: $i - Value: ${array[i]}" done
Output:
Index: 0 - Value: one Index: 1 - Value: two Index: 2 - Value: three
Unset
Use unset to destroy an array. Note that the examples below, exhibit some dubious use of associative arrays:
#1/bin/bash # Create & fill an array ######################################## # declare -A tr echo "Newly declared array: ${tr[@]}" tr[1,1]="hoi"; tr[1,2]="doei" echo "Filled array: ${tr[@]}" # Re-declare doesn't reset ######################################## # declare -A tr echo "Array after redeclaring - It doesn't reset the array:" echo ${tr[@]} # Unset array ######################################## # unset tr echo "Array after unset - Now it's empty: ${tr[@]}" # Unset a non-existing array ######################################## # echo "Unsetting a non-existing array doesn't give an error:" unset ik_besta_niet
Uitvoer:
Newly declared array: Filled array: doei hoi Array after redeclaring - It doesn't reset the array: doei hoi Array after unset - Now it's empty: Unsetting a non-existing array doesn't give an error:
Reading output of a command into an array
I want to use WP-CLI command wp post list
to return IDs of products. I want to store these IDs in an array. Subsequently, I want to use parallelisation to do some nifty stuff with these IDs, without having to wait until tomorrow morning for the results.
This doesn't work:
j=$(wp post list --post_type=product --field=ID --posts_per_page=64)
Eventhough echo ${j[@]}
gives a promising result, I think it's just one string and not an array.
This works [1]:
unset j mapfile -t j < <( wp post list --post_type=product --field=ID --posts_per_page=64 ) echo "Whole array: ${j[@]}" echo "Item 5: ${j[5]}"
Arithmatic with arrays
This works, so no (())
black magic today. At least, not here:
i=5 echo "Entry i (=5): ${j[$i]}" echo "Entry i+1: ${j[$i+1]}" echo "Entry 6: ${j[6]}"
See also
Sources
- https://opensource.com/article/18/5/you-dont-know-bash-intro-bash-arrays
- https://linuxhint.com/associative_array_bash/
- https://stackoverflow.com/questions/11233825/multi-dimensional-arrays-in-bash
- https://stackoverflow.com/questions/3112687/how-to-iterate-over-associative-arrays-in-bash
- https://stackoverflow.com/questions/11426529/reading-output-of-a-command-into-an-array-in-bash