bash return associative array from function

Instead, we could use the respective subject’s names as the keys in our associative array, and the value would be their respective marks gained. How do I check if an array includes an object in JavaScript? How do I remove a particular element from an array in JavaScript? What is the term for diagonal bars which are making rectangular frame more rigid? If someone knows a better way, feel free to add it here. What usually happens? is not used it's previous indirect/double evaluation, but rather in array context it returns the array indices (keys). In 1 Corinthians 7:8, is Paul intentionally undoing Genesis 2:18? First by using for loop and secondly by using foreach. associative arrays. This becomes complicated when there are other positional/getopts parameters. Convert a list to a string. 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. So, if you want to return something, you should use global variables that are updated inside your function. rev 2021.1.8.38287, The best answers are voted up and rise to the top, Super User works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. Unix & Linux: bash silently does function return on (re-)declare of global associative read-only arrayHelpful? You can also initialize an entire associative array in a single statement: aa=([hello]=world [ab]=cd ["key with space"]="hello world") Access an associative array element. Alas, we have been let down by an otherwise superlative bash development team. This trick won't always work (When you have values with whitespaces, or you want to return values that depend on input values), but it usually does the work: Thanks for contributing an answer to Super User! Which 3 daemons to upload on humanoid targets in Cyberpunk 2077? Example: Here array_keys() function is used to find indices names given to them and count() function is used to count number of indices in associative arrays. 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: and then writing a bunch of code inside the function to reassemble the array. How can I pass a key array to a function in bash? The best solution probably is, as already been pointed out, to iterate through the array and copy it step by step. I'm trying to replicate this function I've written in Python that prints a message based on the player and opponents move and compares those moves with an associative array called match. Therefore, ${array} should evaluate to the entire array, indexes and all. and the only answer was: I just want to return array that containing weeks 1,2,3. As such, to pass an array to a function, there is really only one option, and that is to use the nameref feature: Since this is passing by reference, you can also assign to the array in the function. Any use of declare inside a bash function turns the variable it creates local to the scope of that function, meaning we can't access or modify global arrays with it. If a president is impeached and removed from power, do they lose all benefits usually afforded to presidents when they leave office? Many people will not understand the line ... ... because they have never heard of a here string. Bash call function as array element 0 I'm in the process of designing a bash script to execute a number of functions in a sequence (installing packages, cloning repos, for instance) and after completion send a summary report to an email address to whether the installations succeeded or failed. Making statements based on opinion; back them up with references or personal experience. Find memcache request hit rate on linux command line; How to return a value from bash function; Iterate over specific file … They don't return data. Being that case, why not directly look at those variables themselves? In mathematics a function ƒ takes an input, x, and returns an output ƒ(x). Note: After not finding an answer here on Stack Overflow, I posted my somewhat crude solution myself. In that case, this code would work exactly as you might expect it to: Then, passing arrays by value to functions and assigning one array to another would work as the rest of the shell syntax dictates. have a function which reads in values/strings from a file, returning an array: It seems to me as if the function reads the whole file and not line by line, thus putting all strings into a single cell in the array, and I am not sure how to explicitly display clients[0] as this $(clients[0]) fails in bash code, If by an means I am doing something incorrectly, please point this out too or any suggestions on optimising this too. Any third year CS major should know that. 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. Array Assignments. bash - return array from function and display contents, Podcast 302: Programming in PowerPoint can teach you a few things. With a few tricks you can actually pass named parameters to functions, along with arrays. How can I pass an array as parameter to a bash function? Do I have to include my pronouns in a course outline? Requirement: Function to find a string in an array. ... Bash Return Multiple Values from a Function using an Associative Array. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. References. To return values, you can set a global variable with the result, or use command substitution, or you can pass in the name of a variable to use as the result variable. This article will cover some ways you can return values from bash functions: Return value using global variable. Returning a variable from functions in bash script can be little tricky. In BASH script it is possible to create type types of array, an indexed array or associative array. You could use the same technique for copying associative … It allows for only one array being passed, and it being the last element of the parameter list. Use read combined with a here string (<<<) to convert the string into an array. Echo the string. Some are satisfied with converting a list to a string and calling it a day, but if you truly want to deal with an official bash array, the here sting above will do that for you. Bash supports both regular arrays that use integers as the array index, and associative arrays, which use a string as the array index. After some bash self study and experimenting, I am stuck with returning an array from a function, and for the life of me can't see my error. last line of code, You should do a minimal search in google, because this was the first link returned for "bash return array". Commenting on Ken Bertelson solution and answering Jan Hettich: the takes_ary_as_arg descTable[@] optsTable[@] line in try_with_local_arys() function sends: 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: N.B. What specifically is your concern about the script being "easily modified" here? Global variable can be used to return value from a bash function. The += operator allows you to append one or multiple key/value to an associative Bash array. This article will cover some ways you can return values from bash functions: Return value using global variable. Somewhat later Ken posted his solution, but I kept mine here for "historic" reference. In associative array, the key-value pairs are associated with => symbol. Associative arrays can be used when the data is organized by a string, for example, host names. Bash Bonanza Part 4: Arrays 26 September 2017. Especially when you consider that ${array[0]} has no meaning and evaluates to the empty string if the array type is associative. Since bash does not discriminate string from a number, an array can contain a mix of strings and numbers. The examples below describe these different mechanisms. Unlike in many other programming languages, in bash, an array is not a collection of similar elements. If I call doSomething, it might, say, send a string message to stdout. a return, a declare, what sends the array back? Associative arrays are always unordered, they merely associate key-value pairs. 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). Global variable can be used to return value from a bash function. Bash Return Multiple Values from a Function using an Associative Array. You just need to add two lines for each function addition, so I'd call that easily modified. When a microwave oven stops, why are unpopped kernels very hot and popped kernels not hot? If that is true, then you can save something you send to stdout in another context. An associative array can be thought of as a set of two linked arrays -- one holding the data, and the other the keys that index the individual elements of the data array. This solution does not pass an array from a function, but it does allow you to convert the output of a function to an array. What's the difference between 'war' and 'wars'? 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. Bash Array – An array is a collection of elements. Associative arrays (sometimes known as a "hash" or "dict") use arbitrary nonempty strings as keys. Easily stored by outputting to a file, and easily loaded from a file into a script. It's not like bash internally creates a row for 0 with columns labelled 1 and 0. Copying associative arrays is not directly possible in bash. BASH, writing array to nl_012_\n delim string, bash and function to detect duplicate data, Print echo and return value in bash function, Bash block and return codes — need explanation, Display inputs that are redirected from file, Roots given by Solve are not satisfied by the equation, Quantum harmonic oscillator, zero-point energy, and the quantum number n, Counting monomials in product polynomials: Part I, Will RAMPS able to control 4 stepper motors, Ceramic resonator changes and maintains frequency when touched, Draw horizontal line vertically centralized. Method 1: In this method, traverse the entire associative array using foreach loop and display the key elements. Here is sample code to demonstrate it. Bash Arrays | Associative Array Patterns; Bash Functions | Function Patterns; Invocation. First declare an associative array named mx, then execute dig and used sed to convert the output into associative array assignments, then eval that into the current shell. ... Bash Return Multiple Values from a Function using an Associative Array. Why is "I can't get any satisfaction" a double-negative too, according to Steven Pinker? Plus, the mapped variables are all in the local scope, just as $1 (and others). function return values. Copying associative arrays is not directly possible in bash. $ hello 1 2 I got arg1: 1 and arg2: 2 $ hello 3 4 I got arg1: 3 and arg2: 4 $ hello 3 blah bash: printf: blah: invalid number I got arg1: 3 and arg2: 0 You can read more about arrays and functions within Bash here to get a better understanding of the technologies. List Assignment. we can use an eval for the keys, for example: and then a loop using them to create a copy. So, if it had been done right, then the following example would show how the usefulness of arrays in bash could be substantially better: Then, arrays could use the assignment operator, and be passed by value to functions and even other shell scripts. #!/bin/bash # # Associative arrays in bash, take 2 # Using two arrays # Some test values with doublettes values="a a a a b b c d"; # Search for existing keys function getkey {key=$1 How do I tell if a regular file does not exist in Bash? :-). You can only use the declare built-in command with the uppercase “-A” option. An array is a variable that can hold multiple values, where each value has a reference index known as a key. for ~"copies": this technique is good enough, just need to keep aware, that the indices (keys) are gone. I'm trying to replicate this function I've written in Python that prints a message based on the player and opponents move and compares those moves with an associative array called match. Annihilannic. The equivalent of the f es function above could be done with: However a function can modify an array held in the calling script. Syntax listToString may not work with all lines of input. Some are satisfied with converting a list to a string and calling it a day, but if you truly want to deal with an official bash array, the here sting above will do that for you. They only return an exit status. I've read you can echo a value from a function to stand in as a return, but this doesn't work well with associative arrays since it doesn't return a single value that way. As ugly as it is, here is a workaround that works as long as you aren't passing an array explicitly, but a variable corresponding to an array: I'm sure someone can come up with a clearner implementation of the idea, but I've found this to be a better solution than passing an array as "{array[@]"} and then accessing it internally using array_inside=("$@"). UPDATE Test it on your input. Boo! Note: here ! in that case, since it used [@] notation each element is seen by itself as if he was quoted (contrary to [*]). assign the function's return array to array clients, while the function executes, add values DIRECTLY to the clients array. Use array at your leisure. The sed command strips all single quotes, then wraps the variable assignment in, using single-quotes to quote the value. :-) There are probably more things you can do, but let's stop here. It also makes it so that you can create sparse numerically indexed arrays. A simple address database typedef bit bitstream_t[$]; function bitstream_t my_funct(input bitstream_t arg); Dave Rich - Regular arrays should be used when the data is organized numerically, for example, a set of successive iterations. They decided that ${array} was just short hand for ${array[0]}, which was a bad mistake. Bash Return Multiple Values from a Function using an Associative Array. We can loop through the associative array in two ways. User-definable commands. 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. In other words, you can return from a function with an exit status. It allows for only one array being passed, and it being the last element of the parameter list. Example-2: Using Function Command You can receive the return value of a bash function and store it in a variable at the time of calling. Yes you can, but you must use a typedef to define the return type. In computer a shell function name can take an input, $1 and return back the value (true or false) to the script. echo "${!aa[@]}" #Out: hello ab key with space Listing associative array values When it comes to functions in bash, one topic that often comes is returning values.There are many different things that you may return from a function, return values, exit codes, or nothing at all. Traversing the Associative Array: We can traverse associative arrays using loops. If you have come to the point of wanting to return an array from a function, then you are probably aware that you can only return status codes. In the following example, a local variable, retval is used and the value of the local variable is return by the function F2 is assigned in a global variable, getval which is printed later. Unix & Linux: bash silently does function return on (re-)declare of global associative read-only arrayHelpful? Looking for title/author of fantasy book where the Sun is hidden by pollution and it is always winter. For bash, that can be scalar, sparse arrays (associative arrays with keys restricted to positive integers) or associative arrays with non-empty keys (neither key nor values can contain NUL characters). Code: $ cat function_return_array #!/bin/bash function myarray () { a [1]=moja a [3]=three } a [1]=one a [2]=two myarray echo $ {a [1]} echo $ {a [2]} echo $ {a [3]} $ ./function_return_array moja two three $. When a bash function ends its return value is its status: zero for success, non-zero for failure. If you are familiar with Perl, C, or Java, you might think that Bash would use commas to separate array elements, however this is not the case; instead, Bash uses spaces: To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Save the following code to a file (say script1.sh) and run it. 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. Example 37-5. Is there any way to make a nonlethal railgun? Something like this ... Reference: Your UNIX: The Ultimate Guide, 2nd Edition, p. 387 (last para). Bash Associative Array (dictionaries, hash table, or key/value pair) You cannot create an associative array on the fly in Bash. Note: After not finding an answer here on Stack Overflow, I posted my somewhat crude solution myself. Internal. Note: declare cannot be put in a function. It is possible to return an array from a function in bash. It is possible to return an associative array from a function through standard output. It only takes a minute to sign up. I have seen this amongst many others, but this does not make sense to me. This is a slight simplification of DevSolar's solution in that it uses the arguments passed rather than copying them. You can pass multiple arrays as arguments using something like this: arrays - script - bash pass associative array to function, Getting the source directory of a Bash script from within, How to check if a string contains a substring in Bash. To learn more, see our tips on writing great answers. Not ideal, but possible. Array Syntax This is passing, in essence, nothing by value - as usual. Passing arrays as parameters in bash (8) . That being said, I do see the value for generalization, functions thus can get the arrays (or copies) without knowing the names: for real copies: declare-A CONFIG load-config CONFIG echo ${CONFIG ["SOMETHING"]} Function Declaration. In bash, functions don't return values. What can we do with other data in a function that we want to use in another function / context? In the previous entry, we discussed how to use functions in Bash, and finished off with a spooky warning about arrays, and how they will not work with the techniques discussed so far.. Today we will explore that further. Bash Arrays | Associative Array Patterns; Bash Functions | Function Patterns; Invocation. Bash associative array tutorial; Bash check if file begins with a string; Bash shell - check if file or directory exists; Can global variables be modified in bash function? The best solution probably is, as already been pointed out, to iterate through the array and copy it step by step. 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. If you are familiar with Perl, C, or Java, you might think that Bash would use commas to separate array elements, however this is not the case; instead, Bash uses spaces: # Array in Perl my @array = (1, 2, 3, 4); How do I return a failure value from a bash function? What you appear to be attempting to do is "return an associative array from a function to the caller". I asked several times "What does your function do?" I am trying to assign indexes to an associative array in a for loop but I have to use an eval command to make it work, this doesn't seem correct I don't have to do this with regular arrays For example, the following assignment fails without the eval command: #! This solution does not pass an array from a function, but it does allow you to convert the output of a function to an array. In short, what this should/must do is by using a function 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. There is another solution which I used to pass variables to functions. They can return a status (the same as other programs). Bash's functions aren't really *functions* in the mathematical sense, or even in the sense of most high-level computing languages. Is there in bash an array_combine function, where I can create an associative array from two? Let's say we wanted to add new users with a function we made called addAccounts that loops over username arguments. declare-A CONFIG load-config CONFIG echo ${CONFIG ["SOMETHING"]} Function Declaration. update: ok that makes sense, I haven;t come across a post mentioning this, thanks. Some are satisfied with converting a list to a string and calling it a day, but if you truly want to deal with an official bash array, the here sting above will do that for you. For anyone wanting to see how I resolved this: To display a single index position of an array, ref. : 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. Just to add to the accepted answer, as I found it doesn't work well if the array contents are someting like: In this case, each member of the array gets split, so the array the function sees is equivalent to: To get this case to work, the way I found is to pass the variable name to the function, then use eval: The basic problem here is that the bash developer(s) that designed/implemented arrays really screwed the pooch. What should I be looking for? The method I developed allows you to access parameters passed to a function like this: 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)! 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. See also zsh with normal arrays and associative arrays without those restrictions. 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. You could use the same technique for copying associative arrays: ... Posted by 22 days ago. That output can be captured in two different ways. The order of march would be. How to concatenate string variables in Bash. It is just like writing there: See above explanation, which just copies descTable[@] array's values according to the current IFS. See the example showing how to return arrays from functions below. How to return a string from a bash function that contains a filename with spaces? There is another solution which I used to pass variables to functions. What you appear to be attempting to do is "return an associative array from a function to the caller". 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. Find memcache request hit rate on linux command line; How to return a value from bash function; Iterate … Note: This is the somewhat crude solution I posted myself, after not finding an answer here on . echo ${aa[hello]} # Out: world Listing associative array keys. Tag: arrays,linux,bash,samba. Assuming stdout is set to the terminal, at least you can see the contents of a variable or something. I have two arrays one with user names and other with their full names that are actually dynamically generated by wbinfo -u. USR=(user1 … You say. Super User is a question and answer site for computer enthusiasts and power users. Let us say we think option #1 above sounds promising. How can I pass a key array to a function in bash? Bash's functions aren't really *functions* in the mathematical sense, or even in the sense of most high-level computing languages. In other words, associative arrays allow you to look up a value from a table based upon its corresponding string label. Asking for help, clarification, or responding to other answers. Advanced Bash-Scripting Guide: Chapter 27. That is because the BNF does not allow you to put an array range to the right of a function name. This makes it so there can be two types of arrays, numerically indexed and hash indexed (called associative arrays in bash parlance). Could the US military legally refuse to follow a legal, but unethical order? If you want to pass one or more arguments AND an array, I propose this change to the script of @A.B. It should evaluate to the inverse of the assignment statement. This solution does not pass an array from a function, but it does allow you to convert the output of a function to an array. Bash associative array tutorial; Bash check if file begins with a string; Bash shell - check if file or directory exists; Can global variables be modified in bash function? @AnthonyRutledge what would that answer be? It allows for only one array being passed, and it being the last element of the parameter list. If you want to pass one or more arguments AND an array, I propose this change to the script of @A.B. For more serious scripts, consider as mentioned, putting the keys in its own array, and search it while looking up values. Associative array as return value. They are really commands. 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[@]})". Welcome to the fourth part of the Bash Bonanza series! By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. r/bash: A subreddit dedicated to bash scripting. 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). How can I pass an array as parameter to a bash function? Internal. I've declared match in my main function and I need to use this in another function which looks like this: This would take more time, though. An array in BASH is like an array in any other programming language. Sanitizing the string representation of the array … Bash functions are not similar to functions in other languages but these are commands. exit code * string * arrays * associative array * indexed array * side effects; void ; void with side effects; exit code Capture the echoed string with command substitution (see above). 0,1 doesn't mean anything special in associative arrays, that's just the string 0,1. So here is a function that returns an array containing 1,2,3 I've declared match in my main function and I need to use this in another function which looks like this: