bash associative array of arrays

Bash supports one-dimensional numerically indexed and associative arrays types. The way you have written the examples is just as one developer talks to another.. Linux Journal, representing 25+ years of publication, is the original magazine of the global Open Source community. fruit[a] = ‘apple’; fruit[p]=pumpkin. You can think of an array is a variable that can store multiple variables within it. Creating associative arrays. >declare -p item BASH associative array printing, I think you're asking two different things there. Arrays are variable that hold more than one value. declare -A names names[John]=Doe names[Jane]=Doe names[Jim]=Smith names[Angela]=Merkel It caught me before falling into a few pitfalls: you have predictive mind. (In bash 4 you can use declare -g to declare global variables - but in bash 4, you should be using associative arrays … There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Assignments are then made by putting the "key" inside the square mapfile -t a_dummy <<< "$(mysql -u root –disable-column-names –silent -B -e "select * from dummy_tbl;" "$DB_NAME")" It’s been a L.O.N.G time since I went to the net for ‘just bash’ questions (:=), so it was great to hear that bash now has ass.arrays. a loop is an overhead. The case is quite different if you have defined values for $item1 and $item2: >item1=12 An associative array is an array of named keys instead of index values. If you're looking for a shell with better associative array support, try zsh. xkcd sorex[“B”] fruit[b] = 'banana' I know it can very well be done using a loop but for a huge sized array containing almost 500,000 elements, In this example, authors with the same associative array value will be output by reverse order of name. New `K' parameter transformation to display associative arrays … Other examples of Array Basics Shell Script: Re Missing Keys and the “+_” in the examples: this is in fact quite important, and it’s a good thing you quoted it in this guide. Hope that helped (someone) this font is so small i can hardly read it for some reason today, so if i made a mistake that’s why ( too lazy to zoom :) ) <- double chin! yes, Nice Way to show examples. An associative array is an array which uses strings as indices instead of integers. Hi Craig, thanks for the very informative addition. Bash Arrays# One dimensional array with numbered index and associative array types supported in Bash. If not pre-declared, then your example (if NOT preceded by "declare -A"): implicitly performs arithmetic evaluation of the expression "foo", which produces a numeric result of "0", thereby assigning element "0" of *indexed* array "MYMAP". Those are referenced using integers and associative are referenced using strings. Bash Array – An array is a collection of elements. $ ax[foo]=”xkcd”; # Script by … I normally create an indexed array from the sql query result as below: Just to recap: associative arrays are arrays with named key value pairs. Associative arrays. Mitch Frazier is an embedded systems programmer at Emerson Electric Co. Mitch has been a contributor to and a friend of Linux Journal since the early 2000s. done < /tmp/fruit, echo "" item=([0]=”two”), >item=( [0]=”one” [0]=”two ) It doesn’t work because you are piping the output of `cat /tmp/fruit` into a while loop, but the second command in the pipe (the while loop) spawns in a new process. unset MYMAP[$K] babble: bibble Example 37-5. An associative array is an array which uses strings as indices instead of integers. You can initialize elements one at a time as follows: aa[hello]=world aa[ab]=cd aa["key with space"]="hello world" You can also initialize an entire associative array in a single statement: Now, I was brought to your site while searching for a solution to this …, Is there a less clumsy method of sorting keys than this (spaces in keys must be preserverd)…, bash-4.1$ declare -A ARY=( [fribble]=frabble [grabble]=gribble [co bb le]=cribble [babble]=bibble [zibble]=zabble [n o bbl e]=nibble [mobble]=mibble ) https://blog.prakhar.info/array-basics-shell-script/, declare -A MYMAP doesn’t work and throws an error: Bash Arrays# One dimensional array with numbered index and associative array types supported in Bash. You can assign values to arbitrary keys: $ Copyright (C) 2013 Free Software Foundation, Inc. #!/ bin/bash # array-strops.sh: String operations on arrays. So in order to do what you want, the while loop needs to be in the process with the rest of the script. unset MYMAP[‘ ‘] unset MYMAP[ ] To access the last element of a numeral indexed array use the negative indices. array[wow]: command not found In BASH script it is possible to create type types of array, an indexed array or associative array. Print the entire array content. So, if I want the semantics of storing an element in array[abc][def] what I should do is store the value in array["$(keyhash "abc")$(keyhash "def")"] where keyhash looks like this: function keyhash { echo "$1" | sha512sum | cut -c-8 } You can then pull out the elements of the associative array using the same keyhash function. A common use is for counting occurrences of some strings. $ cat /tmp/t.bash To explicitly declare a … $ bash test.sh Count number of elements in bash array, where the name of the array is dynamic (i.e. sorex[“TH”] KEYS=(${!MYMAP[@]}). 3> Create an assoc array from the result of sql query. 11. | while read line; \ You can also subscribe without commenting. flap -> three four And it apparently stays in local scope too. You can use any string or integer as a subscript to access array elements.The subscripts and values of associative arrays are called key value pairs. list incorrectly adds the key as a\ b rather than simply as a b. declare: usage: declare [-afFirtx] [-p] [name[=value] …], using the quotes around the values throws an error like this: On the other hand, if you've ever used any modern Office Suite and seen no, # if [ ${MYMAP[blablabla]+_} ]; then echo yes; else echo no;fi You’re only checking the version of the bash which is found first in your path, not necessarily the one you’re currently running. The best solution probably is, as already been pointed out, to iterate through the array and copy it step by step. Each key in the array can only appear once. Any variable may be used as an indexed array; the declare builtin will explicitly declare an array. There are two types of arrays you can use – indexed and associative arrays. fruit[a] = 'apple' Bash Associative Array (dictionaries, hash table, or key/value pair) You cannot create an associative array on the fly in Bash. This is free software; you are free to change and redistribute it. Unlike most of the programming languages, Bash array elements don’t have to be of the same data type. Associative arrays are always unordered, they merely associate key-value pairs. Bash supports both regular arrays that use integers as the array index, and associative arrays, which use a string as the array index. /home/ubuntu# if [ ${MYMAP[blablabla]} ]; then echo yes; else echo no;fi. echo 1 | awk ‘{ sorex[“W”] GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu) I would prefer it phrased less rudely though. Loop through all key/value pair. If you agree with that, then you probably won't want to read Those are referenced using integers and associative are referenced using strings. If you agree with that, then you probably won't want to read about the "new" associative arrays that were added in version 4.0 of bash. In bash array, the index of the array must be an integer number. bash-4.1$ for key in “${sorted_keys[@]}”; do echo “$key: ${ARY[$key]}”; done You can assign values to arbitrary keys: $ declare -A userdata This is something a lot of people missed. The bash man page has long had the following bug listed: There's nothing too surprising about associative arrays in bash, they are as you probably expect: declare -A aa aa [ hello ]= world aa [ ab ]=cd The -A option declares aa to be an associative array. where $DB_NAME is the variable pointing to DB name string. Since bash does not discriminate string from a number, an array can contain a mix of strings and numbers. echo "fruit[$i] = '${fruit[$i]}'" in the above example, if the variables $item1 and $item2 are un[define]d, then the result would be: this happened because undeclared variables have an implicit value of 0 when used as an indexer, it would be so these two lines are identical: >item=( [item1]=”one” [item2]=”two ) Inside the loop the if statement tests to In other words, associative arrays allow you to look up a value from a table based upon its corresponding string label. Or, you use a non-associative array as well as an associative array. Those are referenced using integers and associative are referenced using strings. Answered all my questions at once. I’m confused about scope. two. Avi, are you sure you are using bash? }, $ bar(){ echo “$1 -> $2”; } Add values to arrays – note the possibility to add values to arrays with += operator. Just arrays, and associative arrays (which are new in Bash 4). In this tutorial we will see how to use bash arrays and perform fundamental operations on them. Yes, but they are not as good as just Now we will present some examples that will elaborate on what all you can do with Associative Arrays in bash: Example1: Accessing the array keys and values. This is a pretty common problem in bash, to reference array within arrays for which you need to create name-references with declare -n.The name following the -n will act as a nameref to the value assigned (after =).Now we treat this variable with nameref attribute to expand as if it were an array and do a full proper quoted array expansion as before. Bash does not support multidimensional arrays. otherwise keys with spaces would split to separate array items. fruit[$t]=$f ; \ An associative array lets you create lists of key and value pairs, instead of just numbered values. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. mobble: mibble In this article, we’ll cover the Bash arrays, and explain how to use them in your Bash scripts. 2> Create a new assoc array from indexed array where values are keys. fruit[c] = 'cranberry' An associative array lets you create lists of key and value pairs, instead of just numbered values. code-bloat at its finest and just think the bash folks are exaggerating a bit, Extending the answer from @AndrewSchulman, using -rn as a global sort option reverses all columns. Thanks for the informative write-up! fruit[p]=pumpkin The += operator allows you to append one or multiple key/value to an associative Bash array. is not true for bash versions <4.2 wherein associative arrays MUST be explicitly created with "declare -A". Associative arrays are supported via typeset -A in Bash 4, Zsh, and Ksh93. This means you could not "map" or "translate" one string to another. ... You can now use full-featured associative arrays. "It's too big and too slow" (at the very bottom of the man page). Bash arrays. So in that subprocess, the variables are being set, but when the while loop terminates the subprocess terminates and the changes to the variables are lost. Some gaps may be present, i.e., indices can be not continuous. To access the last element of a numeral indexed array … There is NO WARRANTY, to the extent permitted by law. The problem with such tips is that they will give the right answer most of the time, leading to even more confusion and frustration when they don’t. Required fields are marked *. It is important to remember that a string holds just one element. Thanks Will, updated. I used to do a lot of bash+cmdline-perl (perl -e) to do what a simple ass.array in bash could have done. I wish I had found it before I spent an hour figuring it out myself. All In bash, you could use the quoted list approach mentioned in the zsh using printf %q or with newer versions ${var@Q}. b banana Associative Arrays. Also, if K is a single or double quote, only the latter one works! The former are arrays in which the keys are ordered integers, while the latter are arrays in which the keys are represented by strings. There are two types of arrays in Bash: indexed arrays – where the values are accessible through an integer index; associative arrays – where the values are accessible through a key (this is also known as a map) In our examples, we’ll mostly be using the first type, but occasionally, we’ll talk about maps as well. A few Bourne-like shells support associative arrays: ksh93 (since 1993), zsh (since 1998), bash (since 2009), though with some differences in behaviour between the 3. for (i in sorex) print i }’, Hi Mark, that code inside the single quotes is all Awk code, not bash. In Ksh93, arrays whose types are not given explicitly are not necessarily indexed. Bash Arrays# One dimensional array with numbered index and associative array types supported in Bash. Don't subscribe echo "${#aa[@]}" # Out: 3 Destroy, Delete, or Unset an Array. There is another solution which I used to pass variables to functions. Bash 4 supports associative arrays, yay! Note: bash version 4 only. $ echo ${ax[bar]:-MISSING}; Note: bash 4 also added associative arrays, but they are implemented slightly differently. Thanks for any clarification. then read on. The subscript is "0", not the string "foo". bash arrays and associative arrays This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. Defining the array. It is also worth noting that one limitation of a BASH arrays is that you cannot create a multidimensional array, such as placing an array within an array. Thanks for the write up but would you consider wrapping “bash version 4 only” at the start of the article in strong tags? A value can appear more than once in an array. Combine Bash associative arrays. In bash array, the index of the array must be an integer number. Also, there is no need to declare the size of an array in advance – arrays can expand/shrink at runtime. flop -> one two. A detailed explanation of bash’s associative array Bash supports associative arrays. In plain English, an indexed array is a list of things prefixed with a number. * //’); \ Multidimensional arrays are not supported, but can be simulated using associative arrays. Regular arrays should be used when the data is organized numerically, for example, a set of successive iterations. done. Note also that the += operator also works with regular variables one Copying associative arrays is not directly possible in bash. Sorry you can’t use it! Here's one I did for an associative array I called master_array: master_array["group_list"]+="${new_group}"; To sequence through the groups in the order you added them, sequence through the group_list field in a for loop, then you can access the group fields in the associative array. And it even appears that way if the array was [declare]d one previously. item to an array with a parenthesis enclosed list if any of the keys have spaces in them. fruit[c] = ‘cranberry’; fruit[p]=pumpkin. san francisco. Bash print associative array. $ bash –version HOW DOES THIS WORK WITHOUT AN ASSIGN??? The following code. Basics. Arrays allow a script to store a collection of data as separate entities using indices. echo “c cranberry” >> /tmp/fruit, declare -A fruit Learn how your comment data is processed. Bash's history commands are unmatched by any other shell (Zsh comes close, but lacks some options, such as the ability to delete by line number). for i in "${!fruit[@]}"; do $ echo ${ax[foo]:-MISSING}; brackets rather than an array index. Let’s define an array of names. ... Bash Array Declaration. name is any name for an array; index could be any number or expression that must evaluate to a number greater than or equal to zero.You can declare an explicit array using declare -a arrayname. Until recently, Bash could only use numbers (more specifically, non-negative integers) as keys of arrays. List all the IP address and calculate how many sites it accessed. Easiest way to check for an index or a key in an array?, To check if the element is set (applies to both indexed and associative array) [ ${ array[key]+abc} ] && echo "exists". Text: Write an example that illustrates the use of bash arrays and associative arrays. bash. We declare an associative array with capital A: Here's my little guide on how to define and access associative arrays in bash. Bash provides support for one-dimensional numerically indexed arrays as well as associative arrays. bash-4.1$ IFS=$’\n’ sorted_keys=( $( echo -e “${keys[@]/%/\n}” | sed -r -e ‘s/^ *//’ -e ‘/^$/d’ | sort ) ) There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. There is no one single true way: the method you'll need depends on where your data comes from and what it is. unset MYMAP[” “] Arrays are one of the most used and fundamental data structures. This might help: https://www.gnu.org/software/gawk/manual/gawk.html. x=2 fribble: frabble Thanks david, good point. $ declare -p MYMAP However, I find that things like: fruit[$t]="$f" Really useful, I was stuck declaring an associative implicitly inside a function, apparently you need declare -A for that to work fine. You can use any string or integer as a subscript to access array elements.The subscripts and values of associative arrays are called key value pairs. You can also assign multiple items at once: You can also use keys that contain spaces or other "strange" characters: Note however that there appears to be a bug when assigning more than one t=$(echo $line|sed -e ‘s/ . In bash, you could use the quoted list approach mentioned in the zsh using printf %q or with newer versions ${var@Q}. about the "new" associative arrays that were added in version 4.0 of bash. Except I can’t see the syntax in any manual or search I’ve done. 6.7 Arrays. Associative array. MISSING However, interactive scripts like .bashrc or completion scripts do not always have this luxury, because it’s a pain to set it, and then unset it, also saving the value which is overhead in the sense of time taken to implement/reimplement each time. $ echo ${ax[foo]:+SET}; echo “fruit[b]=${fruit[‘b’]}” >item=( [item1]=”one” [item2]=”two ), > declare -p item Explains everything about associative arrays in a single article. Writing about Bash is challenging because it's remarkably easy for an article to devolve into a manual that focuses on syntax oddities Keys are unique and values can not be unique. Bash v4 and higher support associative arrays, which are also very useful. bash. bash-4.1$ keys=( ${!ARY[@]} ) Use this higher order function to prevent the pyramid of doom: foreach(){ Creating Arrays. For example, consider the following script: At the top, b["a b"] is assigned a value as part of a parenthesis enclosed You could use the same technique for copying associative arrays: the script to print out all the keys: You can see here that the first assignment, the one done via the Andy: Wow, just have learned how to use associative arrays, via this very handy page! they are as you probably expect: The -A option declares aa to be an associative array. Bas… Four in the morning, still writing Free Software, Moon picture Albuquerque Moon by Jason Bache, used under CC-BY-2.0. Associative arrays (sometimes known as a "hash" or "dict") use arbitrary nonempty strings as keys. Strings are without a doubt the most used parameter type. Funnily, there's a memoized version of keyhash you can write which uses an array … #!/bin/bash OFS=$IFS # store field separator IFS="${2: }" # define field separator file=$1 # input file name unset a # reference to line array unset i j # index unset m n # dimension ### input i=0 while read line do a=A$i unset $a declare -a $a='($line)' i=$((i+1)) done < $file # store number of lines m=$i ### output for ((i=0; i < $m; i++)) do a=A$i # get line size # double escape '\\' for sub shell '``' and 'echo' n=`eval … This also works with associative arrays. fruit[a]= As a RULE, it is good to just declare ALL variables. I’m jealous of this. Bash v4 and higher support associative arrays, which are also very useful. Associative arrays are stored in a 'hash' order. I just tried declare -A MYMAP here and it worked. is not the way to check the version of your current bash? Bash Arrays # Bash supports one-dimensional numerically indexed and associative arrays types. There's nothing too surprising about associative arrays in bash, Bash associative array examples – Andy Balaam's Blog, Update: see also Bash Arrays. You can create an array that contains both strings and numbers. c cranberry Replies to my comments Bash & ksh: echo "${!MYARRAY[@]}" Loop through an associative array. Bash 5.1 allows a very straight forward way to display associative arrays by using the K value as in ${arr[@]@K}: $ declare -A arr $ arr=(k1 v1 k2 v2) $ printf "%s\n" "${arr[@]@K}" k1 "v1" k2 "v2" From the Bash 5.1 description document: hh. To destroy, delete, or … Strings are without a doubt the most used parameter type. For example, two persons in a list can have the same name but need to have different user IDs. if done on a un[define]d variable, will treat it like an -a instead of an -A, which causes the last entry only to be recognized as the first indexer (zero) unless, of course, those items have value. grabble: gribble echo “fruit[c]=${fruit[‘c’]}” We can use any variable as an indexed array without declaring it. sorex[“FR”] At present, I’m struggling to find solution to either of the following problems: Notify me of followup comments via e-mail. Example Copying associative arrays is not directly possible in bash. So, instead you can do: cat >/tmp/fruit <