{"id":18653,"date":"2022-08-23T09:01:21","date_gmt":"2022-08-23T07:01:21","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/?p=18653"},"modified":"2022-11-28T09:12:28","modified_gmt":"2022-11-28T08:12:28","slug":"shell-scripting-how-to-return-values-from-functions-in-bash-scripts","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/","title":{"rendered":"SHELL SCRIPTING: How to return values from functions in bash scripts"},"content":{"rendered":"\n

The shell is designed to be a command interpreter. Shell scrips language, if we can call it so, Initially was used to automate simple administrative tasks and flows.<\/p>\n\n\n\n

Shell scripting was not designed to give all structural languages facilities, as Python<\/a> or Perl<\/a>, for instance. Nevertheless shell scripting, was and it is intensive used by most of unix and DBA’s administrators, scripts reaching several hundred lines of code, in many cases spread over several functions and files.<\/p>\n\n\n\n

Among others, one of big shell scripting limitation is the return values from functions.<\/p>\n\n\n\n\n\n\n\n

With no return<\/code> keyword, the function returned value is the last executed return code of the last command executed in the function. This situation cannot be accepted for a production script, as this is totally arbitrary as returned value.<\/p>\n\n\n

\n#!\/bin\/bash\nfunction my_function() {\n    mkdir \/cannot\/create\/this\/directory\n}\n\n# Execute the my_function\nmy_function\nret=$?\necho "The returned value: $ret"\n<\/pre><\/div>\n\n\n
Output  (The returned value is the error code value of the failing mkdir<\/code> command):<\/p>\n\n\n
\nmkdir: cannot create directory \u2018\/cannot\/create\/this\/directory\u2019: No such file or directory\nThe returned value: 1\n<\/pre><\/div>\n\n\n
Otherwise the return value it the numerical value of the return<\/code> keyword, if it is used. This situation is better than the previous one, but pretty limitative to only numerical values (in fact this is the most used use-case for shell function returns) :<\/p>\n\n\n
\n#!\/bin\/bash\nfunction my_function() {\n    return 99\n}\n\n# Execute the my_function\nmy_function\nret=$?\necho "The returned value: $ret"\n<\/pre><\/div>\n\n\n
Output:<\/p>\n\n\n
\nThe returned value: 99\n<\/pre><\/div>\n\n\n
If there is a need to return one or more arbitrary values, like strings or paths, other method should be used: <\/p>\n\n\n
\n#!\/bin\/bash\nfunction my_function() {\n    local _ret_val1=$1\n    local _ret_val2=$2\n    \n    # ... your code here\n    first_value_to_return="Hello world"\n    second_value_to_return="\/path\/to\/nowhere"\n\n    # return values\n    eval $_ret_val1="'$first_value_to_return'"\n    eval $_ret_val2="'$second_value_to_return'"\n\n    return 0\n}\n\n# Execute the my_function with parameter1 and parameter2\nmy_function parameter1 parameter2\n\nfunction_return_code=$?\n\necho "First value is: $parameter1"\necho "Second value is: $parameter2"\necho "Function return code is: $function_return_code"\n\n<\/pre><\/div>\n\n\n
Output: <\/p>\n\n\n
\nFirst value is: Hello world\nSecond value is: \/path\/to\/nowhere\nFunction return code is: 0\n<\/pre><\/div>\n\n\n
The advantage of this method is that the numerical returned code can be still be used, by using the return<\/code> keyword.<\/p>\n\n\n\n
Conclusion<\/h2>\n\n\n\n
Despite limitation shell scripting is one of the most used “languages” for system admins, DBA’s. Even if there are big limitation, work arounds, like the one presented, exist for any situation.<\/p>\n","protected":false},"excerpt":{"rendered":"
BASH: make function to return arbitrary values, not only numbers<\/p>\n","protected":false},"author":27,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229,42],"tags":[1075,1154],"type_dbi":[],"class_list":["post-18653","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","category-operating-systems","tag-bash","tag-scripts"],"acf":[],"yoast_head":"\nSHELL SCRIPTING: How to return values from functions in bash scripts - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"SHELL SCRIPTING: How to return values from functions in bash scripts\" \/>\n<meta property=\"og:description\" content=\"BASH: make function to return arbitrary values, not only numbers\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\" \/>\n<meta property=\"og:site_name\" content=\"dbi Blog\" \/>\n<meta property=\"article:published_time\" content=\"2022-08-23T07:01:21+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2022-11-28T08:12:28+00:00\" \/>\n<meta name=\"author\" content=\"Oracle Team\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Oracle Team\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\"},\"author\":{\"name\":\"Oracle Team\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#\/schema\/person\/66ab87129f2d357f09971bc7936a77ee\"},\"headline\":\"SHELL SCRIPTING: How to return values from functions in bash scripts\",\"datePublished\":\"2022-08-23T07:01:21+00:00\",\"dateModified\":\"2022-11-28T08:12:28+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\"},\"wordCount\":273,\"commentCount\":2,\"keywords\":[\"Bash\",\"Scripts\"],\"articleSection\":[\"Database Administration & Monitoring\",\"Operating systems\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\",\"url\":\"https:\/\/www.dbi-services.com\/blog\/shell-scripting-how-to-return-values-from-functions-in-bash-scripts\/\",\"name\":\"SHELL SCRIPTING: How to return values from functions in bash scripts - 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