bash return string

To elaborate, the "return value" is always a number. This has the same aliasing problem as the eval solution. The return value is 0 if the string matches the pattern, and 1 otherwise. I'll write the example in java to show what I'd like to do: The example below works in bash, but is there a better way to do this? Apr 26, 2019 Table of Contents. can reference array variables and subscripted array variables. 1 Corinthians 3:15 What does "escaping through the flames" convey? Worthy of mention is that nameref variables are only available since bash 4.3 (according to the. Where can I find Software Requirements Specification for Open Source software? If that isn’t enough, I recommend Markarian451’s solution. When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. 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This is a general-purpose solution: it even allows you to receive a string into a local variable. In this post we will look at some useful and commmonly used string manipulation technques that should come in handy in our every day scripting tasks. Bash return values should probably be called "return codes" because they're less like standard return values in scripting, and more like numeric shell command exit codes (you can do stuff like. What do you call a 'usury' ('bad deal') agreement that doesn't involve a loan? Here are the options available for returning data from a function. ), has explicit support for reference variables or name references (namerefs), beyond "eval", with the same beneficial performance and indirection effect, and which may be clearer in your scripts and also harder to "forget to 'eval' and have to fix this error": A variable can be assigned the nameref attribute using the -n option to the For example “3382” is a substring of “this is a 3382 test”. "Command substitution is far more explicit and modular" would be relevant if the question were about commands; this question is how to return a string, from a bash function! How to check whether a string contains a substring in JavaScript? The speed difference seems even more notable using bash on MSYS where stdout capturing from function calls is almost catastrophic. Let’s say you have a long string with several words separated by a comma or underscore. To assign to the first argument use in function "$1": and branches based on whether it is True (0) or False (not 0). 5. Edit: As a demonstration, see the following program. Inicio » » bash function return string. One advantage with the nameref approach over eval is that one doesn't have to deal with escaping strings. Before executing the sed command we verify that the number of arguments passed to the Bash script is correct. I have a bash shell variable called u = " this is a test ". executing script with no params produces... To illustrate my comment on Andy's answer, with additional file descriptor manipulation to avoid use of /dev/tty: The way you have it is the only way to do this without breaking scope. This answer does have its merits. One possible workaround is an explicit declaration of the passed variable as global: If name "x" is passed as an argument, the second row of the function body will overwrite the previous local declaration. They key problem of any 'named output variable' scheme where the caller can pass in the variable name (whether using eval or declare -n) is inadvertent aliasing, i.e. The original question contains the simplest way to do it, and works well in most cases. Browse other questions tagged bash shell-script command string or ask your own question. But many options are available in bash to remove unwanted characters from string data, such as parameter expansion, sed, awk, xargs, etc. use it consistently in every function you write. inside the function creates a nameref variable ref whose value is the variable How do I split a string on a delimiter in Bash? Bash scripting is quite popular is the easiest scripting language. The options have been all enumerated, I think. bash pattern to return both scalar and array value objects: In my programs, by convention, this is what the pre-existing $REPLY variable is for, which read uses for that exact purpose. Addressing Vicky Ronnen's head up, considering the following code: Maybe the normal scenario is to use the syntax used in the test_inside_a_func function, thus you can use both methods in the majority of cases, although capturing the output is the safer method always working in any situation, mimicking the returning value from a function that you can find in other languages, as Vicky Ronnen correctly pointed out. To remove characters from the starting and end of string data is called trimming. your coworkers to find and share information. For example (EDIT 2: (thank you Ron) namespaced (prefixed) the function-internal variable name, to minimize external variable clashes, which should finally answer properly, the issue raised in the comments by Karsten): Note that the bash "declare" builtin, when used in a function, makes the declared variable "local" by default, and "-n" can also be used with "local". In this post we will look at some useful and commmonly used string manipulation technques that should come in handy in our every day scripting tasks. Identify String Length inside Bash Shell Script. Bash knows only status codes (integers) and strings written to the stdout. declare or local builtin commands (see the descriptions of declare and local Here are the options available for returning data from a function. with the name of a nameref variable as an argument, the variable referenced by⋅ It's ok to send in a local variables since locals are dynamically scoped in bash: You could also capture the function output: Looks weird, but is better than using global variables IMHO. E.g., inside function X, name local variables with convention "X_LOCAL_name". References and assignments to ref are If the control variable in a for loop has the nameref attribute, the list bash how to return string from function. Change ), You are commenting using your Facebook account. Close the temporary fd before returning your string. variables to be manipulated indirectly. generating lists of integers with constraint. One can extract the digits or given string … – Michael Dorst Jul 8 '19 at 13:06 eval will execute whatever is given to it. But the names themselves might still interfere, so if you intend to use the value previously stored in the passed variable prior to write the return value there, be aware that you must copy it into another local variable at the very beginning; otherwise the result will be unpredictable! Some solutions do not allow for that as some forgot about the single quotes around the value to assign. The function always assigns the return value to, From the perspective of the caller, the return value can be assigned to any variable (local or global) including. It would be nice to receive a response from an expert about that answer. That is why I added a name check at the top of myFunction: Note this could also be put into a function itself if you have to check a lot of variables. strips longest match for ‘*.’ which matches “bash.string.” so after striping this, it prints the remaining txt. Bash Split String – Often when working with string literals or message streams, we come across a necessity to split a string into tokens using a delimiter. The delimiter could be a single character or a string with multiple characters. You are free to fail to set the associated value before returning (hence my convention of always nulling it at the start of the function) or to trample its value by calling the function again (possibly indirectly). The value of the global variable will be changed after calling the function. EDIT 1 - (Response to comment below by Karsten) - I cannot add comments below any more, but Karsten's comment got me thinking, so I did the following test which WORKS FINE, AFAICT - Karsten if you read this, please provide an exact set of test steps from the command line, showing the problem you assume exists, because these following steps work just fine: (I ran this just now, after pasting the above function into a bash term - as you can see, the result works just fine.). Like any programming or scripting language, you come across printing text on the terminal. I checked that line for an value, if that is true, i need the regexp match as result back, to get stored in a value. But then that is by convention, NOT actually tied programmatically to the execution of your code. Some are a subset of parameter substitution, and others fall under the functionality of the UNIX expr command. If I still want to use the same name (here: returnVariable) I just create a buffer variable, give that to myFunction and then copy the value returnVariable. Maximum useful resolution for scanning 35mm film. - see my answer below. If you are coming from a C/C++ background, you might be looking for a do-while loop but that one doesn't exist in bash. The correct result would be: ( Log Out /  In bash, variables and functions are not in the same namespace. You want to split this string and extract the individual words. The only way around that is to use a single dedicated output variable like REPLY (as suggested by Evi1M4chine) or a convention like the one suggested by Ron Burk. It's similar to running bash -c "string", but eval executes the command in the current shell environment rather than creating … #!/bin/bash set -x function pass_back_a_string() { eval "$1='foo bar rab oof'" } return_var='' pass_back_a_string return_var echo $return_var Prints "foo bar rab oof". Browse other questions tagged bash shell-script command string or ask your own question. See this answer that explains how to create namerefs in bash functions: +1 @tomas-f : you have to be really careful on what you have in this function "getSomeString()" as having any code which will eventually echo will mean that you get incorrect return string. Choosing one may come down to a matter of the best style for your particular application, and in that vein, I want to offer one particular style I've found useful. Discover details at: http://masteringunixshell.net/qa44/bash-how-to-return-string-from-function.html Usually 0 means success, and non-zero means some kind of failure. I only want to assign values so I use printf -v "${returnVariable}" "%s" "${value}" instead. My previous university email account got hacked and spam messages were sent to many people. What is the current school of thought concerning accuracy of numeric conversions of measurements? Bash has no built-in function to trim string data. This is a simple way to get into global scope a function-scope value, and some would consider this better/simpler than the eval approach to redefine a global variable as outlined by bstpierre. Use the == operator with the [ [ command for pattern matching. In the event that the function also needs to output to console (as @Mani mentions above), create a temporary fd in the beginning of the function and redirect to console. shell functions to refer to a variable whose name is passed as an argument to⋅ Until Loops in Bash. Comparison Operators # Comparison operators are operators that compare values and return true or false. There is a built-in function named trim() for trimming in many standard programming languages. Why are "LOse" and "LOOse" pronounced differently? The Overflow Blog Episode 304: Our stack is HTML and CSS Honestly, it is much simpler than that. The bash if command is a compound command that tests the return value of a test or command ($? ) and I would like to return only the last part of each string. name passed as the first argument. Namerefs can be⋅ First option uses passing argument to the function. When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. You can echo a string, but catch it by piping (|) the function to something else. The string (or text) that the command spits out is referred to as its "output", not its "return value". Bash doesn't have a concept of return types, just exit codes and file descriptors (stdin/out/err, etc). How can so many people ignore combining an. It is best to put these to use when the logic does not get overly complicated. For the purpose of this answer I will assume that you are looking for strings that are permitted to contain any lower or upper case alphabetic characters, numerals, or underscores. Of course, this is only a convention. The length of the string can be counted in bash in multiple ways. $1. This can happen in numerous scenarios such as when you want to output the contents of a file or check the value of a variable. In the following example, a global variable, ‘ retval’ is used. Here is sample code to demonstrate it. Otherwise, if unset is executed How to concatenate string variables in Bash. The array contains in each position the content below: Quote: a.b.c a.d.f a a.d a.b.c.h. Here a listed few of many ways how to extract number from a string. Change ), You are commenting using your Twitter account. (Or in the other direction, I don't want to have to read the source of the function I'm calling just to make sure the output parameter I intend to use is not a local in that function.). I have a bash shell variable called u = " this is a test ". ( Log Out /  Bash scripting is quite popular is the easiest scripting language. If a different user or at least someone with less knowledge about the function (this is likely me in some months time) is using myFunction I do not want them to know that he must use a global return value name or some variable names are forbidden to use. The string you're looking for always has MOM: before it, but you have not said if it always has " after it. where the aim is to exctract nunber 999.Let's start by using tr command: $ NUMBER=$(echo "I am 999 years old." For all the examples below we will use sentence I am 999 years old. You can get the initial value of the variable in the function with. We stop the execution of the script with the exit command and exit code 1 if the number of arguments is incorrect. Making statements based on opinion; back them up with references or personal experience. established for each word in the list, in turn, when the loop is executed. For the purpose of this answer I will assume that you are looking for strings that are permitted to contain any lower or upper case alphabetic characters, numerals, or underscores. Passing parameters works as usual, just put them inside the braces or backticks. However, nameref variables Since all variables in bash are global by default this is easy: function myfunc () { myresult='some value' } myfunc echo $myresult. eval should be a last resort. Is it kidnapping if I steal a car that happens to have a baby in it? So, treating the variable of the same name as the value of the function is a convention that I find minimizes name clashes and enhances readability, if I apply it rigorously. unset using the -n option to the unset builtin. As previously mentioned, the "correct" way to return a string from a function is with command substitution. Join Stack Overflow to learn, share knowledge, and build your career. How can I get the source directory of a Bash script from within the script itself? * strips the longest match for . I suspect others may have the same experience. ÁREA DE CONOCIMIENTO. Playing around with Bash and just really wrestling on how to tokenize a string and return its parts. First option uses passing argument to the function. Bash does not work like regular programming languages when it comes to returning values. The string you're looking for always has MOM: before it, but you have not said if it always has " after it. This can happen in numerous scenarios such as when you want to output the contents of a file or check the value of a variable. Edit: added quoting in the appropriate place to allow whitespace in string to address @Luca Borrione's comment. Syntax: Any of the following syntaxes can be followed to count the length of string. The simplest way to return a value from a bash function is to just set a global variable to the result. return part of a string in bash. ( Log Out /  by the calling function. Turn … Functions in Bash Scripting are a great way to reuse code. If the function also needs to be output to the console (as described in @ Mani), create a temporary fd at the beginning of the function and redirect to the console. If the test returns true, the substring is contained in the string. Bash function can return a string value by using a global variable. The most straightforward and robust solution is to use command substitution, as other people wrote: The downside is performance as this requires a separate process. How to replace all occurrences of a string? But bash has no this type of built-in function. You can return string from function in many ways, but you can not use command "return" to return string: return "Hello..." Return statement can return only a integer value. Can ISPs selectively block a page URL on a HTTPS website leaving its other page URLs alone? It concatenates its arguments into a single string, joining the arguments with spaces, then executes that string as a bash command. I'd like to return a string from a Bash function. In this section of our Bash scripting tutorial you'll learn how they work and what you can do with them.Think of a function as a small script within a script. I was about to say. 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. @Karsten agreed. Options. Your CHECKINPUT and CHECKOUTPUT variables will be empty because your function does not echo nor printf anything. The until loop follows the same syntax as the while loop: until [ condition ]; do [COMMANDS] Done Do electrons actually jump across contacts? Just try using something like this myFunction "date && var2" to some of the supposed solutions here. NEW_STRING: the string we want to replace ORIGINAL_STRING with. specified by the nameref variable's value. Save the following code to a file (say script1.sh) and run it. Example. #Implement a generic return stack for functions: Thanks for contributing an answer to Stack Overflow! Array variables cannot be given the -n attribute. A built in way to do what the OP has asked is available since Bash 4.3 (2014?) Change ), You are commenting using your Google account. In the above example, ##*. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Of course, you can always do something like. The syntax looks like this:Here P is a number that indicates the starting index of the substring and L is the length of the substring. The inadvertent aliasing that breaks encapsulation is the big problem with both the, That has its uses, but on the whole you should avoid making an explicit redirect to the console; the output may already be redirected, or the script may be running in a context where no tty exists. Right way: eval "${returnVariable}='${value}'" or even better: see the next point below. name clashes: From an encapsulation point of view, it's awful to not be able to add or rename a local variable in a function without checking ALL the function's callers first to make sure they're not wanting to pass that same name as the output parameter. Like any programming or scripting language, you come across printing text on the terminal. You could get around that by duplicating, Trouble is that the thing to the right of the pipe is a subshell. Some are a subset of parameter substitution, and others fall under the functionality of the UNIX expr command. ${#string} The above format is used to get the length … Bash can be used to perform some basic string manipulation. in both cases (eval and namerefs), you may have to pick a different name. In this quick tip, you'll learn to split a string into an array in Bash script. All this have to be done in a bash. This answer made me realize that that was just my C#-habits talking. To learn more, see our tips on writing great answers. Playing around with Bash and just really wrestling on how to tokenize a string and return its parts. If you omit the L parameter then the rest of the string is returned, starting from position P.This is different from before with the cut command where we gave the starting and ending indexes. @ElmarZander You're wrong, this is entirely relevant. The code above … How to Split String in Bash Script. Arte, Arquitectura y Diseño; Ciencias Biológicas y Agropecuarias; Ciencias Económico Administrativas; Ciencias Exactas e Ingenierías; Ciencias de la Salud; Ciencias Sociales y Humanidades; … The reason this works is because the call function itself has no locals and uses no variables other than REPLY, avoiding any potential for name clashes. There is a built-in function named trim() for trimming in many standard programming languages. ... BASH_EXECUTION_STRING The command argument to the -c invocation option. At the point where the caller-defined output variable name is assigned, we're effectively in the caller's scope (technically in the identical scope of the call function), rather than in the scope of the function being called. Thank you! Please log in using one of these methods to post your comment: You are commenting using your WordPress.com account. This article will cover some ways you can return values from bash functions: Return value using global variable. as its first argument, running. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. apart from the alternative syntax note, isn't this the exact same thing the op already wrote in his own question? Bash has no built-in function to trim string data. There is another kind of loop that exists in bash. To return the substring starting at position 6 of the whole string, use the following command (there’s a zero-offset, so the first position is zero): echo ${myString:6} If you want to echo a substring that starts at position zero and contains the next six characters, use the following command: Bash supports a surprising number of string manipulation operations. One can extract the digits or given string using various methods. It is my hope that this percolates to the top. How to limit the disruption caused by students not writing required information on their exam until time is up. The other technique suggested in this topic, namely passing the name of a variable to assign to as an argument, has side effects, and I wouldn't recommend it in its basic form. Consider this a proof of concept, but the key points are. All variables declared inside a function will be shared with the calling environment. With spaces, then executes that string as a bash function before and after calling the function take a as! Information on their exam until time is up extract number from a bash.! Are the options available for returning data from a function to a variable name... Into an array of strings in bash single simple statement string or your! The stdout characters bash return string the starting and end of string data is called trimming called trimming in quick. Calls is almost catastrophic scripting is quite popular is the easiest scripting language, you are commenting your... I find very useful if you have certain tasks which need to be performed several times variables and are. Twitter account school of thought concerning accuracy of numeric conversions of measurements since it captures all them. From an expert about that answer -n option to the idea in C++ Match. Some are a subset of parameter substitution, and works well in most cases a global variable will.... Here thinking that I wanted them to put them inside the braces or backticks does. Longest Match for ‘ *. ’ which matches “.string.txt ” after. String we want to return a listed few of many ways how to compare strings in bash from. $ 1: Note the use of explicitly naming output bash return string: Note the use of quoting $! ) the function likewise be used to perform some basic string manipulation array in bash, since version,! Arguments with spaces, then executes that string as a demonstration, see the following can... Still, it prints the remaining txt work in the man page of,... One should e.g reports this usage as deprecated a number the data and... 304: Our stack is HTML and CSS in the appropriate place to allow whitespace string... In way to reuse code turn … bash how to return the last command executed instance, if a file! To something else string in an array in bash an expert about that.... Expr, though ShellCheck reports this usage as deprecated programmatically to the execution your! Above … I have a long string with multiple characters to tokenize a checked... Stdout capturing from function calls is almost catastrophic shell functions to refer to a function... Block a page URL on a HTTPS website leaving its other page URLs alone original question bash return string simplest... It kidnapping if I find very useful if you have a bash function avoid it is incorrect # -habits.... Digits or given string using various methods were a lot of good answers, they all not! My philosophy is that of the string can be followed to count length! Bosses in order to appear important `` this is a string from a string on a delimiter bash. Of capturing echo fails since it captures all of them, is n't this the exact same the. Commenting using your Facebook account is 2 can return a string value is 2 listed few of many how! Array in bash and CSS Identify string length inside bash shell script something. Will avoid interpreting content in $ result as shell special characters ’ is used feb! Variable as the eval solution to address @ Luca Borrione 's comment be... Bash_Execution_String the command argument to the idea in C++ reuse code that, I think fall under the of. '' pronounced differently 3382 test ” string and return True or False order appear. But the key points are heavy use of bash functions way to do what OP! To something else string from a function a proof of concept, but the key points are Twitter.! @ Luca Borrione 's comment be: functions in bash UNIX expr command does...: it even allows you to receive a string is a 3382 test ” string and store into shell... Inconsistent and thus not good for my usage hacked and spam messages were sent to many people each.. Below: Quote: a.b.c a.d.f a a.d a.b.c.h however, nameref variables can array. What the OP already wrote in his own question and just really wrestling how. The -c invocation option values from bash functions: return value is if... Branches based on opinion ; back them up with references or personal experience tied programmatically to the whose value 0! Reports this usage as deprecated shell variable called u = `` this a... ”, you come across printing text on the terminal your Google account itself... Stdout capturing from function 2021 stack Exchange Inc ; user contributions licensed under cc.... Result would be nice to receive a response from an expert about answer. Be used to return written to the sentiment that this percolates to.! We verify that the thing to the bash script Log in using one of these to! Striping it returns “ bash ”, commands may return other values, running Borrione comment. Then executes that string as a status code to be retrieved through $ this percolates to the script... Seems even more notable using bash individual words it, and others under! Multiple ways functions are not in the above example, a global variable can be counted bash. Should e.g also under pdksh and ksh this script does the same just really wrestling how... Its parts selectively block a page URL on a delimiter in bash for my usage a.d a.b.c.h a stance... Always important for managing the complexity of any language whatsoever is commonly used within shell functions to refer a. A listed few of many ways how to compare strings in bash variable... Came in here thinking that I wanted them to multiple echo statements for debugging / logging purposes $. Exist in bash functions are not in the most recent version of bash, version. Not work the way I wanted to return a string is a built-in function named trim ( ) for in. Baby in it be⋅ unset using the -n option to the sentiment that this percolates to the idea C++... Them up with references or personal experience printf anything important for managing the complexity of any language whatsoever feb (. And file descriptors ( stdin/out/err, etc ) damage trigger if cloud rune is.. Passed by references, similar to the bash script remove characters from the alternative Note. For contributing an answer to stack Overflow heavy use of quoting the $ I get the directory... A sign one should e.g the current school of thought concerning accuracy of conversions! References and assignments to the execution of the pipe is a built-in function to a file say! That answer: functions in bash scripting are a subset of parameter substitution, and means. Bash knows only status codes ( integers ) and strings written to the bash script within! Match should be returned into a shell variable called u = `` this is a 3382 ”. Using your Google account command executed descriptors ( stdin/out/err, etc ) ( not 0 ) confusing from. The flames '' convey string … bash how to check if a directory in. Namely 4.2 the examples below we will use sentence I am 999 years old initial value of the last of! The easiest scripting language n't have a concept of return types, just exit codes and descriptors! And printed in this global variable can likewise be used to return result as shell special characters in..., ‘ retval ’ is used the command argument to the right of the pipe is a test.! Syntax Note, is n't this the exact same thing the OP already wrote his. Order to appear important occurs “ in ” return of my function to whitespace. Function creates a nameref variable ref whose value is assigned and printed in this quick tip, you 'll to... Exist in bash is used to return value is 2 substring is nothing but string... Previously mentioned, the conditional expression 's return value is that conventions are always important managing. Wordpress.Com account not work the way I wanted to return a string is a 3382 test string. Below: Quote: a.b.c a.d.f a a.d a.b.c.h other types string from a function can do with. See the following example, a global variable will be shared with the string we to... Your RSS reader is syntactically incorrect, the `` return value is assigned and in... Simple statement, um... no, you are commenting using your Twitter account the array contains in position. Answer ”, you agree to Our terms of service, privacy and. Concept of return types, just put them inside the function take a variable as the first arg and the... According to the stdout over bash return string is that nameref variables can not be given -n. In your scripts trim string data command and exit code 1 if the regular expression syntactically! '' pronounced differently.string.txt ”, after striping it returns “ bash ” do the... That string as a bash command correct result would be nice to a... Non-Zero means some kind of loop that exists in bash or personal experience quick tip, you commenting... Value from a function is invoked before executing the sed command we verify that the thing to the in! And ksh this script does the same aliasing problem as the bash return string solution isn ’ t,... Kidnapping if I steal a car that happens to have a long with! Programming or scripting language variable name passed as an argument to⋅ the function with share.! The regular expression is syntactically incorrect, the `` returned '' variable can be counted in....

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