Getting user input in Bash<\/a> is a topic for another day. Here we’ll assume some level of knowledge in gathering user input. The following script prompts a user for exactly three words (and assumes the user will enter them without issue) and then concatenates these string values into a reply message:<\/p>\n#!\/bin\/bash\r\n\r\n# prompt user for 3 words\r\nread -p \"Enter 3 words: \" w1 w2 w3\r\n\r\n# echo to stdout\r\necho \"Your words are: $w1, $w2, and $w3.\"<\/pre>\nThis uses the read<\/code> tool along with the -p<\/code> flag to\u00a0prompt<\/em> the user for input and then save that input in three variables: $w1<\/code>, $w2<\/code>, $w3<\/code>. With these variable values, the script then uses the echo<\/code> tool to send their values concatenated in a more human-friendly format to stdout<\/code>. The result is as follows:<\/p>\n$ .\/script.sh\r\nEnter 3 words: dog fish cat\r\n\r\nYour words are: dog, fish, and cat.\r\n<\/pre>\nThe first line is the command that runs the script, the second line is the prompt, followed by three words entered by a user: dog<\/code>, fish<\/code>, and cat<\/code>. Finally, a human-friendly form of these variables is echoed in the terminal window (stdout<\/code>). These first two approaches are great for pre-defined texts or even user texts. Now let us consider how one might deal with a lot of text.<\/p>\nUsing Bash to Concatenate Strings in a Loop<\/h2>\n
Concatenating strings in a loop can be useful for a range of applications. One might have texts from multiple sources, large amounts of text, or need to run some filtering logic, or maybe even find the need for some sequential labeling of data.<\/p>\n
For Loop String Concatenation<\/h3>\n
In any case, using for<\/code> loops and while<\/code> loops can be useful helpers in concatenating strings. Fortunately, Bash makes either option easy. Let us first consider an example of using a for<\/span><\/span> loop in bash to concatenate strings:<\/p>\n#!\/bin\/bash\r\n\r\n# define a sentence\r\ntext=\"The only investors that don\u2019t need to diversify are those that are right 100% of the time.\"\r\n\r\n# define unwanted words\r\nstopwords=(\"the\" 'THAT' 'to' 'ARE' 'those' 'of')\r\n\r\n# define output with initiali value of the empty string\r\noutput=''\r\n\r\n# for each word in the text, check if it is wanted.\r\nfor word in $text; do\r\n\r\n # if the lowercase version of word is NOT found in an\r\n # array of the lowercase versions of each word\r\n # in the stopwords array, add it to the output\r\n if ! [[ \"${stopwords[*],,}\" =~ ${word,,} ]]; then\r\n\r\n # concatenate the word to the existing output\r\n # with a trailing space.\r\n output=\"${output}${word} \"\r\n fi\r\ndone\r\n\r\n# send the final output to stdout\r\necho \"Output: $output\"<\/pre>\nIn this short script the following sequence of actions happens:<\/p>\n
\n- A string of text is defined as our source.<\/li>\n
- An array of unwanted words (
stopwords<\/code>) has been defined.<\/li>\n- A
for<\/code> loop is used to loop over each word in the sentence.<\/li>\n- An
if<\/code> statement is used to determine if a word is NOT in the stopwords<\/code> array.<\/li>\n- The
output<\/code> variable is re-defined as its previous form concatenated with the new qualified word, with an ending space for readability.<\/li>\n<\/ol>\nFinally, the end of this Bash script uses the echo<\/code> tool to send the resulting output<\/code> variable to stdout<\/code> where it is displayed in the terminal window as follows:<\/p>\n$ .\/script.sh\r\n\r\nOutput: only investors don\u2019t need diversify right 100% time. \r\n<\/pre>\nHere we see that any words not found in the stopwords<\/code> array (case insensitive matching) has been added to the final output. This is an example of how using a for<\/code> loop in Bash for string concatenation can be a useful approach — one used for filtering unwanted words from a large body of text in this case.<\/p>\nWhile Loop String Concatenation<\/h3>\n
A while<\/code> loop is often desired in cases where a clear termination condition is present. Bash’s for<\/code> loops are\u00a0really<\/em> more akin to the foreach<\/code> concept of taking an action for every item in a collection whereas the while<\/code> loop is more akin to repeating an action until a condition is reached. Let’s consider a simple bash script to use a while<\/code> loop to only extract the first 10 non-whitespace characters of our text:<\/p>\n# define a sentence\r\ntext=\"The only investors that don\u2019t need to diversify are those that are right 100% of the time.\"\r\n\r\n# creates an array of text\r\ntext_array=($text)\r\n\r\n# init an output variable and counter\r\noutput=''\r\ncount=1\r\n\r\n# get words until\r\nwhile [[ $count -lt 11 ]]; do\r\n\r\n # re-define output as previous with next\r\n # word concatenated.\r\n output=\"$output($count)${text_array[$count]} \"\r\n\r\n # C-Style incrementation of count variable\r\n ((count++))\r\ndone\r\n\r\n# echo the resulting output to stdout\r\necho \"$output\"<\/pre>\nHere we see the following sequence of actions executed:<\/p>\n
\n- Define a string of text.<\/li>\n
- Split that string into an array of words.<\/li>\n
- Initialize a
count<\/code> variable with a value of 1.<\/li>\n- Loop through the array until our count reaches 11 (10 total)<\/li>\n
- Add the next member of the
text_array<\/code> to the output string, prefixed with a (count)<\/code> value indicating the number of that addition.<\/li>\n- Increment the
count<\/code> variable using C-style syntax.<\/li>\n<\/ol>\nThe output from this script is as follows:<\/p>\n
$ .\/script.sh\r\n\r\n(1)only (2)investors (3)that (4)don\u2019t (5)need (6)to (7)diversify (8)are (9)those (10)that\r\n<\/pre>\nHere we see only the first 10 words of our text displayed in the terminal window, as expected.<\/p>\n
Note<\/strong>: IntelliJ-based IDEs will nag about the text_array=($text)<\/code> syntax. To eliminate the nag just add # shellcheck disable=SC2206<\/code> above the line.<\/p>\nFinal Thoughts<\/h2>\n
Using Bash string concatenation is a convenient means of handling short-order scripting needs. It lacks the robustness of formal programming languages but offers the trade-off of simplified syntax. Using Bash along with other *nix tools like read<\/code>, cat<\/code>, and cut<\/code> can make even\u00a0shorter<\/em> order of concatenating strings.<\/p>\nHere we’ve seen Bash applied to string concatenation in an explicit case, a for<\/code> loop, a while<\/code> loop, and even via getting user input. These approaches are not meant to illustrate an exhaustive selection of ways to concatenate strings using Bash scripting — rather just intended to be the seeds of inspiration.<\/p>\n","protected":false},"excerpt":{"rendered":"Bash is a shell programming language designed to provide developers a means to write quick-and-dirty scripts to automate repetitive tasks. It integrates with Linux\/Unix tools like grep, cat, and more but also provides language tools like loops and the means to manipulate stings — including string concatenation. Using bash to concatenate strings is almost eerily […]<\/p>\n","protected":false},"author":2,"featured_media":3352,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[10],"tags":[736,671,738,737,363],"acf":[],"_links":{"self":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/3348"}],"collection":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/comments?post=3348"}],"version-history":[{"count":2,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/3348\/revisions"}],"predecessor-version":[{"id":3353,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/3348\/revisions\/3353"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media\/3352"}],"wp:attachment":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media?parent=3348"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/categories?post=3348"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/tags?post=3348"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}