bash script that reads user input and uses “cal” command to validate dates












3















I want to write a script that reads my input (for example if my script is called "check", then I would type "check 9 4 1993" and that input would go through the cal command and will check through the calendar whether it is a valid date or not).



My idea below is that if the input that goes through the cal command gives an error it will mean that it's not a valid date, and vice-versa if there's no error than the date is valid. I do realize there's something terribly wrong with this draft (I can't figure out how to make it so that my input will go through the cal command), but I will appreciate some suggestions. Here's the draft anyways:



#!/bin/bash

day=$1; month=$2; year=$3
day=$(echo "$day" | bc)
month=$(echo "$month" | bc)
year=$(echo "$year" | bc)

cal $day $ month $year 2> /dev/null
if [[$? -eq 0 ]]; then
echo "This is a valid date"
else
echo "This is an invalid date"
fi









share|improve this question




















  • 1





    similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

    – glenn jackman
    Oct 8 '14 at 15:48













  • What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

    – Digital Trauma
    Oct 8 '14 at 16:28






  • 1





    Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

    – G-Man
    Oct 8 '14 at 16:33
















3















I want to write a script that reads my input (for example if my script is called "check", then I would type "check 9 4 1993" and that input would go through the cal command and will check through the calendar whether it is a valid date or not).



My idea below is that if the input that goes through the cal command gives an error it will mean that it's not a valid date, and vice-versa if there's no error than the date is valid. I do realize there's something terribly wrong with this draft (I can't figure out how to make it so that my input will go through the cal command), but I will appreciate some suggestions. Here's the draft anyways:



#!/bin/bash

day=$1; month=$2; year=$3
day=$(echo "$day" | bc)
month=$(echo "$month" | bc)
year=$(echo "$year" | bc)

cal $day $ month $year 2> /dev/null
if [[$? -eq 0 ]]; then
echo "This is a valid date"
else
echo "This is an invalid date"
fi









share|improve this question




















  • 1





    similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

    – glenn jackman
    Oct 8 '14 at 15:48













  • What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

    – Digital Trauma
    Oct 8 '14 at 16:28






  • 1





    Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

    – G-Man
    Oct 8 '14 at 16:33














3












3








3








I want to write a script that reads my input (for example if my script is called "check", then I would type "check 9 4 1993" and that input would go through the cal command and will check through the calendar whether it is a valid date or not).



My idea below is that if the input that goes through the cal command gives an error it will mean that it's not a valid date, and vice-versa if there's no error than the date is valid. I do realize there's something terribly wrong with this draft (I can't figure out how to make it so that my input will go through the cal command), but I will appreciate some suggestions. Here's the draft anyways:



#!/bin/bash

day=$1; month=$2; year=$3
day=$(echo "$day" | bc)
month=$(echo "$month" | bc)
year=$(echo "$year" | bc)

cal $day $ month $year 2> /dev/null
if [[$? -eq 0 ]]; then
echo "This is a valid date"
else
echo "This is an invalid date"
fi









share|improve this question
















I want to write a script that reads my input (for example if my script is called "check", then I would type "check 9 4 1993" and that input would go through the cal command and will check through the calendar whether it is a valid date or not).



My idea below is that if the input that goes through the cal command gives an error it will mean that it's not a valid date, and vice-versa if there's no error than the date is valid. I do realize there's something terribly wrong with this draft (I can't figure out how to make it so that my input will go through the cal command), but I will appreciate some suggestions. Here's the draft anyways:



#!/bin/bash

day=$1; month=$2; year=$3
day=$(echo "$day" | bc)
month=$(echo "$month" | bc)
year=$(echo "$year" | bc)

cal $day $ month $year 2> /dev/null
if [[$? -eq 0 ]]; then
echo "This is a valid date"
else
echo "This is an invalid date"
fi






bash shell-script scripting cal






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jan 13 at 21:51









Rui F Ribeiro

39.5k1479133




39.5k1479133










asked Oct 8 '14 at 15:32









grinkegrinke

163




163








  • 1





    similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

    – glenn jackman
    Oct 8 '14 at 15:48













  • What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

    – Digital Trauma
    Oct 8 '14 at 16:28






  • 1





    Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

    – G-Man
    Oct 8 '14 at 16:33














  • 1





    similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

    – glenn jackman
    Oct 8 '14 at 15:48













  • What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

    – Digital Trauma
    Oct 8 '14 at 16:28






  • 1





    Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

    – G-Man
    Oct 8 '14 at 16:33








1




1





similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

– glenn jackman
Oct 8 '14 at 15:48







similar question, not dup: just wanted to know what am i doing wrong in the end of this script that doesnt put my checkdate in to cal command

– glenn jackman
Oct 8 '14 at 15:48















What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

– Digital Trauma
Oct 8 '14 at 16:28





What is the purpose behind day=$(echo "$day" | bc)? Input validation? Removal of leading zeros?. In either case you could also do day=$((10#$day)) which uses the shell's own arithmetic expansion instead of forking a bc process.

– Digital Trauma
Oct 8 '14 at 16:28




1




1





Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

– G-Man
Oct 8 '14 at 16:33





Almost exactly the same problem as in bash question about if and then; and very similar to how to write this if command?

– G-Man
Oct 8 '14 at 16:33










3 Answers
3






active

oldest

votes


















3














In some Linux distros that I have checked (e,g, Ubuntu 14.04), the packaged cal comes from BSD and not GNU Coreutils. The BSD version does not seem to accept days as a parameter; only months and years. The Ubuntu version does have a -H YYYY-MM-DD option, but that doesn't seem to help.



Instead I would use the date utility. Assuming the GNU Coreutils under Linux I think I would rewrite your script something like:



#!/bin/bash

day=$((10#$1))
month=$((10#$2))
year=$((10#$3))

if date -d $year-$month-$day > /dev/null 2>&1; then
# cal $month $year
echo "This is a valid date"
else
echo "This is an invalid date"
fi


Notes:




  • I am using the shell's own arithmetic expansion to validate input/remove leading zeros, instead of forking a new bc process for each parameter

  • I am using GNU date to parse the input date

  • The date command may be used directly as the if conditional expression. if works by checking process exit codes. Commonly the [ or [[ executables are used instead, but there is no reason other programs can be used if they exit with useful exit codes

  • I'm not sure if you actually wanted the cal output for correct dates or not. If you do, simply uncomment the cal line.






share|improve this answer































    1














    [[ is actually a command, and like other commands you need whitespace to separate its arguments:



    if [[ $? -eq 0 ]]; then
    # ...^





    share|improve this answer































      1














      There is a space between your dollar $ and your month variable:



      cal $day $ month $year 2> /dev/null


      It should be:



      cal $day $month $year 2> /dev/null





      share|improve this answer


























      • Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

        – grinke
        Oct 8 '14 at 17:16











      Your Answer








      StackExchange.ready(function() {
      var channelOptions = {
      tags: "".split(" "),
      id: "106"
      };
      initTagRenderer("".split(" "), "".split(" "), channelOptions);

      StackExchange.using("externalEditor", function() {
      // Have to fire editor after snippets, if snippets enabled
      if (StackExchange.settings.snippets.snippetsEnabled) {
      StackExchange.using("snippets", function() {
      createEditor();
      });
      }
      else {
      createEditor();
      }
      });

      function createEditor() {
      StackExchange.prepareEditor({
      heartbeatType: 'answer',
      autoActivateHeartbeat: false,
      convertImagesToLinks: false,
      noModals: true,
      showLowRepImageUploadWarning: true,
      reputationToPostImages: null,
      bindNavPrevention: true,
      postfix: "",
      imageUploader: {
      brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
      contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
      allowUrls: true
      },
      onDemand: true,
      discardSelector: ".discard-answer"
      ,immediatelyShowMarkdownHelp:true
      });


      }
      });














      draft saved

      draft discarded


















      StackExchange.ready(
      function () {
      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f160064%2fbash-script-that-reads-user-input-and-uses-cal-command-to-validate-dates%23new-answer', 'question_page');
      }
      );

      Post as a guest















      Required, but never shown

























      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      3














      In some Linux distros that I have checked (e,g, Ubuntu 14.04), the packaged cal comes from BSD and not GNU Coreutils. The BSD version does not seem to accept days as a parameter; only months and years. The Ubuntu version does have a -H YYYY-MM-DD option, but that doesn't seem to help.



      Instead I would use the date utility. Assuming the GNU Coreutils under Linux I think I would rewrite your script something like:



      #!/bin/bash

      day=$((10#$1))
      month=$((10#$2))
      year=$((10#$3))

      if date -d $year-$month-$day > /dev/null 2>&1; then
      # cal $month $year
      echo "This is a valid date"
      else
      echo "This is an invalid date"
      fi


      Notes:




      • I am using the shell's own arithmetic expansion to validate input/remove leading zeros, instead of forking a new bc process for each parameter

      • I am using GNU date to parse the input date

      • The date command may be used directly as the if conditional expression. if works by checking process exit codes. Commonly the [ or [[ executables are used instead, but there is no reason other programs can be used if they exit with useful exit codes

      • I'm not sure if you actually wanted the cal output for correct dates or not. If you do, simply uncomment the cal line.






      share|improve this answer




























        3














        In some Linux distros that I have checked (e,g, Ubuntu 14.04), the packaged cal comes from BSD and not GNU Coreutils. The BSD version does not seem to accept days as a parameter; only months and years. The Ubuntu version does have a -H YYYY-MM-DD option, but that doesn't seem to help.



        Instead I would use the date utility. Assuming the GNU Coreutils under Linux I think I would rewrite your script something like:



        #!/bin/bash

        day=$((10#$1))
        month=$((10#$2))
        year=$((10#$3))

        if date -d $year-$month-$day > /dev/null 2>&1; then
        # cal $month $year
        echo "This is a valid date"
        else
        echo "This is an invalid date"
        fi


        Notes:




        • I am using the shell's own arithmetic expansion to validate input/remove leading zeros, instead of forking a new bc process for each parameter

        • I am using GNU date to parse the input date

        • The date command may be used directly as the if conditional expression. if works by checking process exit codes. Commonly the [ or [[ executables are used instead, but there is no reason other programs can be used if they exit with useful exit codes

        • I'm not sure if you actually wanted the cal output for correct dates or not. If you do, simply uncomment the cal line.






        share|improve this answer


























          3












          3








          3







          In some Linux distros that I have checked (e,g, Ubuntu 14.04), the packaged cal comes from BSD and not GNU Coreutils. The BSD version does not seem to accept days as a parameter; only months and years. The Ubuntu version does have a -H YYYY-MM-DD option, but that doesn't seem to help.



          Instead I would use the date utility. Assuming the GNU Coreutils under Linux I think I would rewrite your script something like:



          #!/bin/bash

          day=$((10#$1))
          month=$((10#$2))
          year=$((10#$3))

          if date -d $year-$month-$day > /dev/null 2>&1; then
          # cal $month $year
          echo "This is a valid date"
          else
          echo "This is an invalid date"
          fi


          Notes:




          • I am using the shell's own arithmetic expansion to validate input/remove leading zeros, instead of forking a new bc process for each parameter

          • I am using GNU date to parse the input date

          • The date command may be used directly as the if conditional expression. if works by checking process exit codes. Commonly the [ or [[ executables are used instead, but there is no reason other programs can be used if they exit with useful exit codes

          • I'm not sure if you actually wanted the cal output for correct dates or not. If you do, simply uncomment the cal line.






          share|improve this answer













          In some Linux distros that I have checked (e,g, Ubuntu 14.04), the packaged cal comes from BSD and not GNU Coreutils. The BSD version does not seem to accept days as a parameter; only months and years. The Ubuntu version does have a -H YYYY-MM-DD option, but that doesn't seem to help.



          Instead I would use the date utility. Assuming the GNU Coreutils under Linux I think I would rewrite your script something like:



          #!/bin/bash

          day=$((10#$1))
          month=$((10#$2))
          year=$((10#$3))

          if date -d $year-$month-$day > /dev/null 2>&1; then
          # cal $month $year
          echo "This is a valid date"
          else
          echo "This is an invalid date"
          fi


          Notes:




          • I am using the shell's own arithmetic expansion to validate input/remove leading zeros, instead of forking a new bc process for each parameter

          • I am using GNU date to parse the input date

          • The date command may be used directly as the if conditional expression. if works by checking process exit codes. Commonly the [ or [[ executables are used instead, but there is no reason other programs can be used if they exit with useful exit codes

          • I'm not sure if you actually wanted the cal output for correct dates or not. If you do, simply uncomment the cal line.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Oct 8 '14 at 17:24









          Digital TraumaDigital Trauma

          5,83211528




          5,83211528

























              1














              [[ is actually a command, and like other commands you need whitespace to separate its arguments:



              if [[ $? -eq 0 ]]; then
              # ...^





              share|improve this answer




























                1














                [[ is actually a command, and like other commands you need whitespace to separate its arguments:



                if [[ $? -eq 0 ]]; then
                # ...^





                share|improve this answer


























                  1












                  1








                  1







                  [[ is actually a command, and like other commands you need whitespace to separate its arguments:



                  if [[ $? -eq 0 ]]; then
                  # ...^





                  share|improve this answer













                  [[ is actually a command, and like other commands you need whitespace to separate its arguments:



                  if [[ $? -eq 0 ]]; then
                  # ...^






                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Oct 8 '14 at 15:45









                  glenn jackmanglenn jackman

                  51k571110




                  51k571110























                      1














                      There is a space between your dollar $ and your month variable:



                      cal $day $ month $year 2> /dev/null


                      It should be:



                      cal $day $month $year 2> /dev/null





                      share|improve this answer


























                      • Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                        – grinke
                        Oct 8 '14 at 17:16
















                      1














                      There is a space between your dollar $ and your month variable:



                      cal $day $ month $year 2> /dev/null


                      It should be:



                      cal $day $month $year 2> /dev/null





                      share|improve this answer


























                      • Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                        – grinke
                        Oct 8 '14 at 17:16














                      1












                      1








                      1







                      There is a space between your dollar $ and your month variable:



                      cal $day $ month $year 2> /dev/null


                      It should be:



                      cal $day $month $year 2> /dev/null





                      share|improve this answer















                      There is a space between your dollar $ and your month variable:



                      cal $day $ month $year 2> /dev/null


                      It should be:



                      cal $day $month $year 2> /dev/null






                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited Oct 9 '14 at 7:55

























                      answered Oct 8 '14 at 15:43









                      geedoubleyageedoubleya

                      3,0131118




                      3,0131118













                      • Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                        – grinke
                        Oct 8 '14 at 17:16



















                      • Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                        – grinke
                        Oct 8 '14 at 17:16

















                      Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                      – grinke
                      Oct 8 '14 at 17:16





                      Damn, what a rookie mistake by me, thanks for noticing :) The script works as intended now, i have the right output.

                      – grinke
                      Oct 8 '14 at 17:16


















                      draft saved

                      draft discarded




















































                      Thanks for contributing an answer to Unix & Linux Stack Exchange!


                      • Please be sure to answer the question. Provide details and share your research!

                      But avoid



                      • Asking for help, clarification, or responding to other answers.

                      • Making statements based on opinion; back them up with references or personal experience.


                      To learn more, see our tips on writing great answers.




                      draft saved


                      draft discarded














                      StackExchange.ready(
                      function () {
                      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f160064%2fbash-script-that-reads-user-input-and-uses-cal-command-to-validate-dates%23new-answer', 'question_page');
                      }
                      );

                      Post as a guest















                      Required, but never shown





















































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown

































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown







                      Popular posts from this blog

                      How to make a Squid Proxy server?

                      Is this a new Fibonacci Identity?

                      19世紀