{"id":4796,"date":"2024-04-14T03:00:00","date_gmt":"2024-04-14T07:00:00","guid":{"rendered":"https:\/\/www.both.org\/?p=4796"},"modified":"2024-04-05T14:39:27","modified_gmt":"2024-04-05T18:39:27","slug":"learn-bash-by-writing-a-number-guessing-game","status":"publish","type":"post","link":"https:\/\/www.both.org\/?p=4796","title":{"rendered":"Learn Bash by writing a number guessing game"},"content":{"rendered":"
\r\n
\r\n \r\n <\/i>\r\n <\/a>\r\n <\/span>\r\n<\/div><\/div>\n

Whenever I try to learn a new language, whether it\u2019s a new shell scripting language or a new programming language to write larger programs, I focus on a few things: defining variables, writing statements, and evaluating expressions. Once I understand how to do those concepts, I can usually figure out the rest on my own. Most programming languages share some similarities, so learning the rest is usually a matter of working out the details.<\/p>\n\n\n\n

I like to write a few \u201ctest\u201d or \u201cscratch\u201d programs to practice a new programming language. One sample program I use frequently as an example is the classic \u201cguess the number\u201d program, where the computer picks a number in a range and prompts me to guess the secret number. This exercises how to assign values, how to write statements, and how to evaluate and compare values.<\/p>\n\n\n\n

If you\u2019d like to learn how to write shell scripts in Bash, you can use the \u201cguess the number\u201d program to practice Bash scripting.<\/p>\n\n\n\n

A brief introduction to Bash<\/h2>\n\n\n\n

GNU Bash<\/strong> is the standard shell for most Linux system. Its name comes from the original Unix shell, which was just named sh<\/code>. Later, Unix added support for other shells, including ksh<\/code> for the Korn Shell, and bsh<\/code> for the Bourne Shell. Bash is actually short for the \u201cBourne Again Shell,\u201d a play on the original \u201cBourne Shell\u201d name on older \u201cBig Unix\u201d systems.<\/p>\n\n\n\n

Bash supports all the features of bsh<\/code> but adds several other useful features. Its backwards compatibility with classic Unix shells makes it a popular choice on many Linux systems.<\/p>\n\n\n\n

Guess the number in Bash<\/h2>\n\n\n\n

To write a \u201cguess the number\u201d script in Bash, we need to do a few things:<\/p>\n\n\n\n

    \n
  1. Pick a random number from 1 to 100, and save it to a variable (secret<\/code>)<\/li>\n\n\n\n
  2. Enter a loop where the user enters their guess, and the script says if the guess is too high or too low<\/li>\n\n\n\n
  3. Exit the loop when the user guesses the secret number<\/li>\n<\/ol>\n\n\n\n

    To select a random value, you can use the\u00a0$RANDOM<\/code>\u00a0internal variable. The name of the variable is actually\u00a0RANDOM<\/code>\u00a0and you can reference the\u00a0value<\/em>\u00a0of the variable with the dollar sign in front:\u00a0$RANDOM<\/code>\u00a0will always generate a random number, usually a large number.<\/p>\n\n\n\n

    You can use the \u201cmodulo\u201d arithmetic operator (%<\/code>) to divide the random number by another number and get the remainder<\/em>. For example, 21 % 10<\/code> is 1, because 21 divided by 10 is 2, with 1 left over. But 20 % 10<\/code> is 0, because 10 goes into 20 exactly twice, with nothing left over. That means $RANDOM % 100<\/code> will give values between zero and 99. To make the secret number between 1 and 100, use $RANDOM % 100 + 1<\/code>.<\/p>\n\n\n\n

    Bash provides arithmetic expansion<\/em> using the $(( ))<\/code> notation, so use this to calculate a random number from 1 to 100 and save it in a new variable called secret<\/code>:<\/p>\n\n\n\n

    secret=$(( $RANDOM % 100 + 1 ))<\/code><\/pre>\n\n\n\n
    Next, set a variable to store the user\u2019s guess. We can initialize it to zero with:<\/p>\n\n\n\n
    guess=0<\/code><\/pre>\n\n\n\n
    To start a loop that will continue only if the user\u2019s guess is not<\/em> equal to the secret number, use:<\/p>\n\n\n\n
    while [ \"0$guess\" -ne $secret ] ; do\n...\ndone<\/code><\/pre>\n\n\n\n
    In this example, I\u2019ve used \"0$guess<\/code> to prepend a zero in front of the user\u2019s guess, in case the user types a non-digit value like m<\/code>. The -ne<\/code> comparison test will only work with numbers, so 0m -ne 50<\/code> will test what we want: that the number value<\/em> of 0 is not equal<\/em> to 50, if the secret number was 50.<\/p>\n\n\n\n
    Get values from the user with the read<\/code> statement:<\/p>\n\n\n\n
    read guess<\/code><\/pre>\n\n\n\n
    You can test if one number is less than<\/em> another using the -lt<\/code> comparison, and greater than<\/em> using the -gt<\/code> test. You can use an if<\/code> block in Bash to do each test, but a one-line shortcut uses &&<\/code> to basically say \u201cif this test on the left is true<\/em> then do this task on the right<\/em>. For example, you could add two tests to print if the user\u2019s guess was too low or too high:<\/p>\n\n\n\n
    [ \"0$guess\" -lt $secret ] && echo \"Too low\"\n[ \"0$guess\" -gt $secret ] && echo \"Too high\"<\/code><\/pre>\n\n\n\n
    Putting it all together<\/h2>\n\n\n\n
    Let\u2019s combine what we\u2019ve learned about Bash scripting in this file, called guess<\/code>:<\/p>\n\n\n\n
    #!\/bin\/bash\n\nsecret=$(( $RANDOM % 100 + 1 ))\n\nguess=0\necho \"Guess a number between 1 and 100\"\n\nwhile [ \"0$guess\" -ne $secret ] ; do\n    read guess\n    [ \"0$guess\" -lt $secret ] && echo \"Too low\"\n    [ \"0$guess\" -gt $secret ] && echo \"Too high\"\ndone\n\necho \"That's right!\"<\/code><\/pre>\n\n\n\n
    I\u2019ve added an echo<\/code> statement at the top to tell the user what the script will do, and another echo<\/code> statement at the end to let the user know when they\u2019ve guessed the number.<\/p>\n\n\n\n
    Make this script executable with the chmod<\/code> command:<\/p>\n\n\n\n
    $ chmod +x guess<\/code><\/pre>\n\n\n\n
    And now you can run your script whenever you want to play the \u201cguess the number\u201d game:<\/p>\n\n\n\n
    $ .\/guess\nGuess a number between 1 and 100\n50\nToo high\n25\nToo low\n33\nToo high\n30\nToo high\n28\nToo high\n27\nThat's right!<\/code><\/pre>\n\n\n\n
    Every time you run the script, the $RANDOM<\/code> internal variable gives a new number, so you\u2019ll always have a random secret number between 1 and 100:<\/p>\n\n\n\n
    $ .\/guess\nGuess a number between 1 and 100\n50\nToo low\n75\nToo low\n88\nToo high\n80\nToo low\n84\nThat's right!<\/code><\/pre>\n\n\n\n
    Learning is fun<\/h2>\n\n\n\n
    This \u201cguess the number\u201d game is a great introductory program when learning a new programming language because it exercises several common programming concepts in a pretty straightforward way. By implementing this simple game in different programming languages, you can demonstrate some core concepts and compare details in each language.<\/p>\n","protected":false},"excerpt":{"rendered":"
    Learning a new programming language can be a fun exercise.<\/p>\n","protected":false},"author":33,"featured_media":4314,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[149,69,150],"tags":[151,147,91,152],"class_list":["post-4796","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bash","category-fun","category-programming","tag-bash","tag-fun","tag-linux","tag-programming"],"modified_by":"Jim Hall","_links":{"self":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/4796","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4796"}],"version-history":[{"count":1,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/4796\/revisions"}],"predecessor-version":[{"id":4797,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/4796\/revisions\/4797"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/media\/4314"}],"wp:attachment":[{"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4796"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4796"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4796"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}