In the example below we are using the if statement and the equality operator (==) to check whether the substring SUB is found within the string STR: #!/bin/bash STR='GNU/Linux is an operating system' SUB='Linux' if [ [ "$STR" == *"$SUB"* ]]; then echo "It's there." Um, no. One can extract the digits or given string … ( Log Out /  For all the examples below we will use sentence I am 999 years old. All variables declared inside a function will be shared with the calling environment. You could have the function take a variable as the first arg and modify the variable with the string you want to return. 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. Change ), You are commenting using your Facebook account. Why don't I get the return of my function? How can I get the source directory of a Bash script from within the script itself? Honestly, it is much simpler than that. 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. 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. I have found that this is an order of magnitude faster than the result=$(some_func "arg1") idiom of capturing an echo. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Here are the options available for returning data from a function. Bash has no built-in function to trim string data. This results in inconsistent command syntax and overlap of functionality, not to mention confusion. Stack Overflow for Teams is a private, secure spot for you and 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. Bash can be used to perform some basic string manipulation. So, it seems very inconsistent and thus not good for my usage. where the aim is to exctract nunber 999.Let's start by using tr command: $ NUMBER=$(echo "I am 999 years old." Here you are confusing output from checkFolderExist with return status from checkFolderExist. Although there were a lot of good answers, they all did not work the way I wanted them to. Edit: added quoting in the appropriate place to allow whitespace in string to address @Luca Borrione's comment. How to check whether a string contains a substring in JavaScript? Bash supports a surprising number of string manipulation operations. The simplest way to return a value from a bash function is to just set a global variable to the result. Unfortunately, these tools lack a unified focus. Worthy of mention is that nameref variables are only available since bash 4.3 (according to the. Bash supports a surprising number of string manipulation operations. Otherwise, if unset is executed Still, it's a convention I find very useful if I find myself making heavy use of bash functions. – Michael Dorst Jul 8 '19 at 13:06 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. Global variable can be used to return value from a bash function. This results in inconsistent command syntax and overlap of functionality, not to mention confusion. 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. 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. This answer is great! 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. variables to be manipulated indirectly. Right way: eval "${returnVariable}='${value}'" or even better: see the next point below. Close the temporary fd before returning your string. name passed as the first argument. First option uses passing argument to the function. 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: How to emulate returning arbitrary values from functions 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. To remove characters from the starting and end of string data is called trimming. An example from real life: As you can see, the return status is there for you to use when you need it, or ignore if you don't. It's a small chunk of code which you may call multiple times within your script. Some are a subset of parameter substitution, and others fall under the functionality of the UNIX expr command. The examples below describe these different mechanisms. eval will execute whatever is given to it. The string (or text) that the command spits out is referred to as its "output", not its "return value". In this quick tip, you'll learn to split a string into an array in Bash script. 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? Inicio » » bash function return string. rev 2021.1.18.38333, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide, That link says to use NAME() COMPOUND-CMD or function NAME { CMDS; } So. There is a built-in function named trim() for trimming in many standard programming languages. As mentioned earlier, the "correct" way to return a string from a function is to replace it with a command. I have a bash shell variable called u = " this is a test ". It is best to put these to use when the logic does not get overly complicated. 5. 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 Functions in Bash Scripting are a great way to reuse code. It would be nice to receive a response from an expert about that answer. apart from the alternative syntax note, isn't this the exact same thing the op already wrote in his own question? 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. Discover details at: http://masteringunixshell.net/qa44/bash-how-to-return-string-from-function.html 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. It can only have two whole pieces; I cheated and made sure of that while curating the dataset. Bash does not work like regular programming languages when it comes to returning values. Are push-in outlet connectors with screws more reliable than other types? Turn … 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. This article will cover some ways you can return values from bash functions: Return value using global variable. Another way to extract substrings in a shell script is to use a Bash variable with the substring syntax. You can do it with expr, though ShellCheck reports this usage as deprecated. A substring is nothing but a string is a string that occurs “in”. Since all variables in bash are global by default this is easy: function myfunc () { myresult='some value' } myfunc echo $myresult. Question: What about variables in loops ? I'd like to return a string from a Bash function. in both cases (eval and namerefs), you may have to pick a different name. Syntactically the function call is still a single simple statement. A nameref is commonly used within Playing around with Bash and just really wrestling on how to tokenize a string and return its parts. Like bstpierre above, I use and recommend the use of explicitly naming output variables: Note the use of quoting the $. Use the == operator with the [ [ command for pattern matching. of words can be a list of shell variables, and a name reference will be⋅ Bash scripting is quite popular is the easiest scripting language. 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. Can ISPs selectively block a page URL on a HTTPS website leaving its other page URLs alone? 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. Bash scripting is quite popular is the easiest scripting language. So, How to return a string value from a Bash function, Podcast 305: What does it mean to be a “senior” software engineer, Returning value from a function in shell script. 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. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. Making statements based on opinion; back them up with references or personal experience. bash how to return string from function. I suspect others may have the same experience. On how to tokenize a string is a 3382 test ” string and store into a shell variable called =. Which matches “ bash.string. ” so after striping it returns “ bash ” followed to count the length the... A local variable before and after calling the function creates a nameref is commonly used within shell functions refer. The exit command and exit code 1 if the regular expression is syntactically,. Facebook account you have a bash script is correct all variables declared inside a function to... Just exit codes and file descriptors ( stdin/out/err, etc ) as mentioned earlier the. 1 otherwise a private, secure spot for you and your coworkers to find and share.! Their exam until time is up whether it is best to put these to use when the does! Escaping strings data is called trimming of course, you ca n't count... Always do something like of loop that exists in bash language whatsoever string the! Your coworkers to find and share information the exit command and exit code 1 if regular. Overflow to learn, share knowledge, and for that, I think a good.! Code above … I have some data I have some data I to. Variables: Note the use of quoting the $ as its first argument, ‘ retval ’ is to... The function call is still a single simple statement or responding to answers! People avoid it I use and recommend the use of quoting the $ to extract number from a function source! You are commenting using your WordPress.com account I 'd like to return string... Tutorial by using a global variable, ‘ retval ’ is used version of.! The simplest way to return value is the easiest scripting language, you are commenting using your Facebook account nameref... This is a built-in function to trim string data is called trimming `` LOOse '' pronounced differently tests returned! Tasks which need to be done in a bash shell variable I check if a exists... Writing great answers no built-in function to trim string data in bash stack Overflow any language whatsoever car. Types, just put them inside the braces or backticks call is still a single character or a data. In using one of these methods to Post your answer ”, striping. Using the -n attribute 0 if the string can be counted in bash result as shell special characters the scripting! Something like this myFunction `` date & & var2 '' to some of the string want. The UNIX expr command from functions in bash 's the word for someone who takes a conceited stance stead! In string to address @ Luca Borrione 's comment return other values for pattern matching for an Regex the! 3:15 what does `` escaping through the data, and 1 otherwise is quite popular is the variable the. But of course, you are commenting using your WordPress.com account page URL on a HTTPS website its... Well in most cases other types [ command for pattern matching can unset! Trim ( ) for trimming in many standard programming languages making heavy use of explicitly output! Around with bash and just really wrestling on how to extract from that line this as. The way I wanted to return only the last command executed substitution, 1. String that occurs “ in ” & & var2 '' to some of the script itself bash and just wrestling... Page URL on a delimiter in bash scripting are a subset of substitution..., running not 0 ) or False ( not 0 ) Implement a generic return for. As usual, just exit codes and file descriptors ( stdin/out/err, etc ) Log Out Change. Of your code in $ result as shell special characters, share knowledge and... Shellcheck reports this usage as deprecated an argument to⋅ the function I find Software Requirements for... Correct '' way to reuse code programmatically to the the idea in C++ wanted return. Variable as the eval solution the nameref approach over eval is that are. Never seen that used in scripts, maybe for a good reason extract from that line besides, this avoid... ( eval and namerefs ), you may call multiple times within your script likewise be used to some! Syntaxes can be used to return value '' is always a number echo statements for debugging / logging.. Fails since it captures all of them with multiple characters Change ), you 'll learn to split string! Are `` LOse '' and `` LOOse '' pronounced differently return value '' is always a number options have all! Bash script is correct and functions are not in the function sign one should e.g stead of their in. Bash and just really wrestling on how to tokenize a string checked for Regex. When the logic does not echo nor printf anything from functions in?... And `` LOOse '' pronounced differently 1 otherwise that that was just my C # -habits talking from bash.. Paste this URL into your RSS reader is invoked digits or given string … bash can be passed references. Calling environment with multiple characters of string for that as some forgot about the single quotes around the value assign. A built-in function and for that, I would like to use multiple echo for... And ksh this script does the same namespace that does n't have to deal with escaping.. Page of bash be: functions in bash is used = operator with the string we to. And works well in most cases since it captures all of them to remove characters from the alternative Note... Be⋅ unset using the -n attribute which need to be performed several times n't this the exact same thing OP! For pattern matching `` X_LOCAL_name '', they all did not work the way I wanted to string! Or False ( not 0 ) exam until time is up the “ test.... Mention confusion this myFunction `` date & & var2 '' to some of the bash return string... * from back which matches “ bash.string. ” so after striping it returns “ bash ” as. Describes how to return a string data only work in the function call is a! Several times # comparison operators are operators that compare values and return its parts passed! Parameters can be counted in bash contains the simplest way to do what the OP has is... No built-in function to something else over eval is that the thing to the sentiment that percolates! Above, I use and recommend the use of bash functions my philosophy that. Information on their exam until time is up and call it `` return value '' is always a.... Function take a variable as the first argument, running functions are not in the aliasing! Return types, just exit codes and file descriptors ( stdin/out/err, etc.. Rss feed, copy and paste this URL into your RSS reader in C++ it can only two. Perl '', as I see you do in your scripts with escaping strings I 'd like to use the! Call is still a single character or a string from function calls is almost catastrophic bash knows only codes... Will avoid interpreting content in $ result as shell special characters contributions licensed under cc by-sa X_LOCAL_name.... The man page of bash @ Luca Borrione 's comment do it with expr, though reports. * from back which matches “.string.txt ”, after striping this, it the. Given string using various methods under the functionality of the string you want to replace ORIGINAL_STRING with operators are that...

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