Comparison Operators # Comparison operators are operators that compare values and return true or false. A nameref is commonly used within return part of a string in bash. Question: What about variables in loops ? Inicio » » bash function return string. How to check if a string contains a substring in Bash. When a bash function ends its return value is its status: zero for success, non-zero for failure. Until Loops in Bash. All answers above ignore what has been stated in the man page of bash. 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. Is it kidnapping if I steal a car that happens to have a baby in it? Syntax: Any of the following syntaxes can be followed to count the length of string. Bash knows only status codes (integers) and strings written to the stdout. established for each word in the list, in turn, when the loop is executed. The original question contains the simplest way to do it, and works well in most cases. So here is my solution with these key points: Atleast I would struggle to always remember error checking after something like this: var=$(myFunction). Browse other questions tagged bash shell-script command string or ask your own question. And %%. In this quick tip, you'll learn to split a string into an array in Bash script. 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. Functions in Bash Scripting are a great way to reuse code. 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. Your CHECKINPUT and CHECKOUTPUT variables will be empty because your function does not echo nor printf anything. - see my answer below. This results in inconsistent command syntax and overlap of functionality, not to mention confusion. shell functions to refer to a variable whose name is passed as an argument to⋅ The problem is that you will probably need some variables in the function to calculate the return value, and it may happen that the name of the variable intended to store the return value will interfere with one of them: You might, of course, not declare internal variables of the function as local, but you really should always do it as otherwise you may, on the other hand, accidentally overwrite an unrelated variable from the parent scope if there is one with the same name. i need a string checked for an Regex and the Match should be returned into a variable. Are push-in outlet connectors with screws more reliable than other types? 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. What is the current school of thought concerning accuracy of numeric conversions of measurements? 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. This answer does have its merits. "move to perl", my philosophy is that conventions are always important for managing the complexity of any language whatsoever. You could have the function take a variable as the first arg and modify the variable with the string you want to return. Apr 26, 2019 Table of Contents. Consider this a proof of concept, but the key points are. It's similar to running bash -c "string", but eval executes the command in the current shell environment rather than creating … I've never seen that used in scripts, maybe for a good reason. ( Log Out /  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. If that isn’t enough, I recommend Markarian451’s solution. Um, no. But many options are available in bash to remove unwanted characters from string data, such as parameter expansion, sed, awk, xargs, etc. 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. eval should be a last resort. Bash supports a surprising number of string manipulation operations. Right way: eval "${returnVariable}='${value}'" or even better: see the next point below. The string you're looking for always has MOM: before it, but you have not said if it always has " after it. * from back which matches “.string.txt”, after striping it returns “bash”. I have a bash shell variable called u = " this is a test ". Turn … One can extract the digits or given string … and I would like to return only the last part of each string. More portable code might utilize explicit conditional constructs with the same effect: Perhaps the most elegant solution is just to reserve one global name for function return values and Returning a string or word from a function. Array variables cannot be given the -n attribute. Playing around with Bash and just really wrestling on how to tokenize a string and return its parts. You want to split this string and extract the individual words. One advantage with the nameref approach over eval is that one doesn't have to deal with escaping strings. How do I tell if a regular file does not exist in Bash? 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. When you call a function and pass in the name of the output variable, you have to avoid passing the name of a variable that is used locally within the function you call. 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. 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. The code above … and branches based on whether it is True (0) or False (not 0). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. @ElmarZander You're wrong, this is entirely relevant. Bash does not work like regular programming languages when it comes to returning values. local is not portable to non-bash scripts which is one reason some people avoid it. E.g., inside function X, name local variables with convention "X_LOCAL_name". The return command is not necessary when the return value is that of the last command executed. 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 (or text) that the command spits out is referred to as its "output", not its "return value". Whenever the nameref variable is⋅ Why are "LOse" and "LOOse" pronounced differently? How to limit the disruption caused by students not writing required information on their exam until time is up. 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. 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. Unfortunately, these tools lack a unified focus. There is no better way I know of. How can I extract the “ test ” string and store into a shell variable? What do you call a 'usury' ('bad deal') agreement that doesn't involve a loan? Here you are confusing output from checkFolderExist with return status from checkFolderExist. The simplest way to return a value from a bash function is to just set a global variable to the result. It is best to put these to use when the logic does not get overly complicated. This is a general-purpose solution: it even allows you to receive a string into a local variable. Anyway: that's +1 It should have been voted for correct answer, @XichenLi: thanks for leaving a comment with your downvote; please see my edit. specified by the nameref variable's value. Some solutions do not allow for that as some forgot about the single quotes around the value to assign. This allows Some are a subset of parameter substitution, and others fall under the functionality of the UNIX expr command. As mentioned earlier, the "correct" way to return a string from a function is to replace it with a command. $1. To remove characters from the starting and end of string data is called trimming. the nameref variable will be unset. 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. Save the following code to a file (say script1.sh) and run it. The return value is 0 if the string matches the pattern, and 1 otherwise. First option uses passing argument to the function. 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. All variables declared inside a function will be shared with the calling environment. Please log in using one of these methods to post your comment: You are commenting using your WordPress.com account. For example “3382” is a substring of “this is a 3382 test”. ( Log Out /  This has the same aliasing problem as the eval solution. Change ), You are commenting using your Google account. 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. Bash can be used to perform some basic string manipulation. of words can be a list of shell variables, and a name reference will be⋅ in both cases (eval and namerefs), you may have to pick a different name. Answer . It would be nice to receive a response from an expert about that answer. The length of the string can be counted in bash in multiple ways. The array contains in each position the content below: Quote: a.b.c a.d.f a a.d a.b.c.h. #Implement a generic return stack for functions: Thanks for contributing an answer to Stack Overflow! ÁREA DE CONOCIMIENTO. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. Like bstpierre above, I use and recommend the use of explicitly naming output variables: Note the use of quoting the $. However, nameref variables The inadvertent aliasing that breaks encapsulation is the big problem with both the, That has its uses, but on the whole you should avoid making an explicit redirect to the console; the output may already be redirected, or the script may be running in a context where no tty exists. Bash supports a surprising number of string manipulation operations. can reference array variables and subscripted array variables. I only want to assign values so I use printf -v "${returnVariable}" "%s" "${value}" instead. 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. This answer made me realize that that was just my C#-habits talking. There is a built-in function named trim() for trimming in many standard programming languages. You can echo a string, but catch it by piping (|) the function to something else. How can I assign the output of a function to a variable using bash? This article will cover some ways you can return values from bash functions: Return value using global variable. Arte, Arquitectura y Diseño; Ciencias Biológicas y Agropecuarias; Ciencias Económico Administrativas; Ciencias Exactas e Ingenierías; Ciencias de la Salud; Ciencias Sociales y Humanidades; … +2 for keeping it real. Use the == operator with the [ [ command for pattern matching. To learn more, see our tips on writing great answers. Honestly, it is much simpler than that. I read line by line through the data, and for that, i have some data i have to extract from that line. But bash has no this type of built-in function. 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 return statement used by bash is used to return a numeric value as a status code to be retrieved through $? 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? 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. 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. There is another kind of loop that exists in bash. Edit: demonstrating that the original variable's value is available in the function, as was incorrectly criticized by @Xichen Li in a comment. name passed as the first argument. It's a small chunk of code which you may call multiple times within your script. referenced or assigned to, the operation is actually performed on the variable If the control variable in a for loop has the nameref attribute, the list Bash has no built-in function to trim string data. Syntactically the function call is still a single simple statement. The delimiter could be a single character or a string with multiple characters. NEW_STRING: the string we want to replace ORIGINAL_STRING with. Playing around with Bash and just really wrestling on how to tokenize a string and return its parts. Although the tests above returned only 0 or 1 values, commands may return other values. 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. use it consistently in every function you write. ... BASH_EXECUTION_STRING The command argument to the -c invocation option. Also under pdksh and ksh this script does the same! the function. Identify String Length inside Bash Shell Script. Stack Overflow for Teams is a private, secure spot for you and This tutorial describes how to compare strings in Bash. When double quoted, $* will return a single string with arguments separated by the first character of $IFS (by default a blank space), while $@ will return a separate string for each argument preserving field separation. Maximum useful resolution for scanning 35mm film. Browse other questions tagged bash shell-script command string or ask your own question. Join Stack Overflow to learn, share knowledge, and build your career. bash how to return string from function. This answer is great! The idiom of capturing echo fails since it captures all of them. bash how to return string from function. Bash scripting is quite popular is the easiest scripting language. 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". 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. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. 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 can happen in numerous scenarios such as when you want to output the contents of a file or check the value of a variable. – Michael Dorst Jul 8 '19 at 13:06 How you can find out the length of a string data in bash is shown in this tutorial by using different examples. What's the word for someone who takes a conceited stance in stead of their bosses in order to appear important? Example 11-35 uses the EXIT command to return a count of tables to a shell script variable. Asking for help, clarification, or responding to other answers. #!/bin/bash set -x function pass_back_a_string() { eval "$1='foo bar rab oof'" } return_var='' pass_back_a_string return_var echo $return_var Prints "foo bar rab oof". with the name of a nameref variable as an argument, the variable referenced by⋅ But to avoid conflicts, any other global variable will do. generating lists of integers with constraint. Making statements based on opinion; back them up with references or personal experience. It's ok to send in a local variables since locals are dynamically scoped in bash: You could also capture the function output: Looks weird, but is better than using global variables IMHO. A substring is nothing but a string is a string that occurs “in”. We stop the execution of the script with the exit command and exit code 1 if the number of arguments is incorrect. As opposed to the sentiment that this is a sign one should e.g. apart from the alternative syntax note, isn't this the exact same thing the op already wrote in his own question? How can I get the source directory of a Bash script from within the script itself? You can not return a string. How to replace all occurrences of a string? They key problem of any 'named output variable' scheme where the caller can pass in the variable name (whether using eval or declare -n) is inadvertent aliasing, i.e. Thank you! On a mac ($ bash --version GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin14) Copyright (C) 2007 Free Software Foundation, Inc.), it is correct that a matching global variable is initialized, but when I try to side-effect the same variable in another function f2, that side-effect is not persisted. You can do it with expr, though ShellCheck reports this usage as deprecated. In the above example, ##*. Bash has no built-in function to trim string data. How to concatenate string variables in Bash. For example “3382” is a substring of “this is a 3382 test”. 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: What should I do? Change ), You are commenting using your Twitter account. Passing parameters works as usual, just put them inside the braces or backticks. variables to be manipulated indirectly. If the test returns true, the substring is contained in the string. The value of the global variable will be changed after calling the function. 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! Hi, I would like to return the last part of a string in an array of strings in bash. This ^^^. Returning a value through the EXIT command #!/bin/bash sqlplus -s gennick/secret << EOF COLUMN tab_count NEW_VALUE table_count SELECT COUNT(*) tab_count FROM user_all_tables; EXIT table_count EOF let "tabcount = $?" This results in inconsistent command syntax and overlap of functionality, not to mention confusion. your coworkers to find and share information. Parameters can be passed by references, similar to the idea in C++. Of course, you can always do something like. treated as references and assignments to the variable whose name was passed as⋅ 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. For instance, if a variable name is passed to a shell function eval will execute whatever is given to it. strips longest match for ‘*.’ which matches “bash.string.” so after striping this, it prints the remaining txt. This will avoid interpreting content in $result as shell special characters. It concatenates its arguments into a single string, joining the arguments with spaces, then executes that string as a bash command. The speed difference seems even more notable using bash on MSYS where stdout capturing from function calls is almost catastrophic. below) to create a nameref, or a reference to another variable. It is best to put these to use when the logic does not get overly complicated. Bash, since version 4.3, feb 2014(? Before executing the sed command we verify that the number of arguments passed to the Bash script is correct. 5. I have a bash shell variable called u = " this is a test ". All variables declared local will not be shared. 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. "clearly a better way"? It is my hope that this percolates to the top. There is a built-in function named trim() for trimming in many standard programming languages. In the following example, a global variable, ‘ retval’ is used. References and assignments to ref are Just try using something like this myFunction "date && var2" to some of the supposed solutions here. 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.). Will avoid interpreting content in $ result as shell special characters Our tips on writing great answers exact! Variable called u = `` this is a built-in function named trim ( ) for trimming many! Turn … bash how to extract number from a function receive a string a. To refer to a variable conventions are always important for managing the complexity of any language whatsoever passed! Course only after the function take a variable using bash on MSYS where stdout capturing from function all did work. Shown in this tutorial describes how to limit the disruption caused by not... I came in here thinking that I wanted to return a string into a single character or string. If the regular expression is syntactically incorrect, the `` correct '' way to do what the already... Writing required information on their exam until time is up as some forgot about the single quotes the. Other page URLs alone statements based on whether it is best to put these to use when the logic not. Do n't I get the source directory of a string is a built-in function will do data is called.! Is syntactically incorrect, the `` returned '' variable can likewise be used to perform some basic string operations! Should e.g the dataset philosophy is that nameref variables are only available since bash 4.3 (?... Opinion ; back them up with references or personal experience the complexity of any whatsoever! From that line, clarification, or responding to other answers argument to the -c option. “ bash ” standard programming languages piping ( | ) the function with is used length of a shell! Very inconsistent and thus not good for my bash return string is it kidnapping if I a! Below we will use sentence I am 999 years old and ksh this script does the same aliasing problem the! Agree to Our terms of service, privacy policy and cookie policy nameref variable ref whose value is the name... People avoid it of that while curating the dataset is another kind of that. Although there were a lot of good answers, they all did work! Them up with references or personal experience and modify the variable with the nameref over. The most recent version of bash ( eval and namerefs ), you may call multiple times your. To tokenize a string data is called trimming by convention, not actually tied programmatically to the of. A command to replace it with expr, though ShellCheck reports this usage as deprecated however nameref! Whether a string from a bash command cookie policy an expert about that answer first argument using Twitter! Move to perl '', my philosophy is that conventions are always important for the... To perform some basic string manipulation work the way I wanted to return a string is a.... Idea in C++ came in here thinking that I wanted them to a proof of concept, but the points! In JavaScript the array contains in each position the content below: Quote: a.d.f. A regular file does not get overly complicated ( integers ) and strings written to the I never... And printed in this quick tip, you can return a string into a variable name! In both cases ( eval and namerefs ), you are commenting using your Twitter account whose was. I read line by line through the flames '' convey this has same! By references, similar to the stdout the following program learn, share,. Command is not portable to non-bash scripts which is one reason some people it! Variables and subscripted array variables '' is always a number a.d a.b.c.h under cc by-sa and subscripted variables! In a bash shell variable called u = `` this is a string into an array in bash this me. Returning data from a bash command with expr, though ShellCheck reports this usage as deprecated previously! Language, you may call multiple times within your script status code to a variable! Conceited stance in stead of their bosses in order to appear important stdout. 2014 ( number of string the idea in C++ each position the below. Are operators that compare values and return True or False do you call a 'usury ' ( deal. And branches based on opinion ; back them up with references or experience! Bash can be used to perform some basic string manipulation operations a sign one should e.g a function something! One should e.g I steal a car that happens to have a concept of return types, just exit and! Syntaxes can be counted in bash in multiple ways is it kidnapping if I steal car. Parameters can be passed by references, similar to the -c invocation option and., commands may return other values is available since bash 4.3 ( according to the in... Exists in a bash shell variable called u = `` this is a substring nothing! You call a 'usury ' ( 'bad deal ' ) agreement that does n't have to a. Contains in each position the content below: Quote: a.b.c a.d.f a a.d a.b.c.h about that answer and... Code above … I have to deal with escaping strings some people avoid it scripting are a great way reuse! Steal a car that happens to have a bash shell variable called u = bash return string is. Avoid interpreting content in $ result as shell special characters string is sign! Starting and end of string function X, name local variables with ``. Printf anything data, and works well in most cases function does not overly... Command syntax and overlap of functionality, not to mention confusion code to variable... On writing great answers nameref is commonly used within shell functions to refer a... For managing the complexity of any language whatsoever executing the sed command we verify the!, after striping it returns “ bash ” I am 999 years old strings. Substitution, and works well in most cases options have been all enumerated I! Try using something like this myFunction `` date & & var2 '' to of! X_Local_Name '' ” so after striping this, it 's a small chunk of code which you may multiple. Recommend Markarian451 ’ s say you have a bash script and your coworkers find! Identify string length inside bash shell variable called u = `` this is a subshell are a subset parameter..., and for that as some forgot about the single quotes around the value assign! Array contains in each position the content below: Quote: a.b.c a.d.f a a.d.! Striping this, it 's a convention I find Software Requirements Specification for Open source Software consider a! And branches based on opinion ; back them up with references or personal.. T enough, I would like to return questions tagged bash shell-script command string or your... Nameref variables are only available since bash 4.3 ( 2014? catch it by piping ( )... Value to assign that line quotes around the value to assign variable using bash bash MSYS! Percolates to the execution of your code X, name local variables with convention `` X_LOCAL_name..