An example of how to use getopts in bash

Question

I want to call myscript file in this way       myscript -s 45 -p any string   or      myscript -h   should display help     myscript      should display help   My requirements are    getopt here to get the input arguments check that -s exists  if not return an error check that the value after the -s is 45 or 90 check that the -p exists and there is an input string after if the user enters   myscript -h or just   myscript then display help   I tried so far this code      bin bash while getopts  h s   arg  do   case  arg in     h        echo  usage                s        strength  OPTARG       echo  strength            esac done   But with that code I get errors   How to do it with Bash and getopt

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getops  and  getopt  are very limited  While  getopt  is suggested not to be used at all  it does offer long options  Where as  getopts  does only allow single character options such as  -a   -b   There are a few more disadvantages when using either one   So i ve written a small script that replaces  getopts  and  getopt    It s a start  it could probably be improved a lot   Update 08-04-2020  I ve added support for hyphens e g   --package-name        Usage     script sh package install --package  name with space    --build --archive      Example    parseArguments          echo    ARG 0   - gt  package   echo    ARG 1   - gt  install   echo    ARG PACKAGE   - gt   name with space    echo    ARG BUILD   - gt  1  true    echo    ARG ARCHIVE   - gt  1  true  function parseArguments       PREVIOUS ITEM      COUNT 0   for CURRENT ITEM in          do     if      CURRENT ITEM      --       then       printf -v  ARG   formatArgument    CURRENT ITEM       s   1    could set this to empty string and check with   -z    ARG ITEM-x     if it s set  but empty      else       if     PREVIOUS ITEM     --       then         printf -v  ARG   formatArgument    PREVIOUS ITEM       s     CURRENT ITEM         else         printf -v  ARG   COUNT     s     CURRENT ITEM         fi     fi      PREVIOUS ITEM    CURRENT ITEM          COUNT        done      Format argument  function formatArgument       ARGUMENT    1       Capitalize    ARGUMENT    ARGUMENT --      Remove  --     ARGUMENT    ARGUMENT  -       Replace  -  with        echo    ARGUMENT

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The problem with the original code is that    h  expects parameter where it shouldn t  so change it into just h  without colon  to expect -p any string  you need to add p  to the argument list   Basically   after the option means it requires the argument     The basic syntax of getopts is  see  man bash    getopts OPTSTRING VARNAME  ARGS       where    OPTSTRING is string with list of expected arguments    h - check for option -h  without parameters  gives error on unsupported options  h  - check for option -h with parameter  gives errors on unsupported options  abc - check for options -a  -b  -c  gives errors on unsupported options   abc - check for options -a  -b  -c  silences errors on unsupported options   Notes  In other words  colon in front of options allows you handle the errors in your code  Variable will contain   in the case of unsupported option    in the case of missing value   OPTARG - is set to current argument value  OPTERR - indicates if Bash should display error messages    So the code can be      usr bin env bash usage     echo   0 usage    amp  amp  grep           0  exit 0         -eq 0    amp  amp  usage while getopts   hs p   arg  do   case  arg in     p    Specify p value        echo  p is   OPTARG                s    Specify strength  either 45 or 90        strength   OPTARG           strength -eq 45 -o  strength -eq 90              amp  amp  echo  Strength is  strength                echo  Strength needs to be either 45 or 90   strength found instead                h        Display help        usage       exit 0            esac done   Example usage       foo sh    foo sh usage      p    Specify p value      s    Specify strength  either 45 or 90      h        Display help      foo sh -s 123 -p any string Strength needs to be either 45 or 90  123 found instead  p is any string     foo sh -s 90 -p any string Strength is 90  p is any string   See  Small getopts tutorial at Bash Hackers Wiki

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Use getopt  Why getopt   To parse elaborated command-line arguments to avoid confusion and clarify the options we are parsing so that reader of the commands can understand what s happening   What is getopt   getopt is used to break up  parse  options in command lines for easy parsing by shell procedures  and to check for legal options  It uses the GNU getopt 3  routines to do this   getopt can have following types of options    No-value options key-value pair options   Note  In this document  during explaining syntax    Anything inside     is optional parameter in the syntax examples   is a place holder  which mean it should be substituted with an actual value    HOW TO USE getopt   Syntax  First Form  getopt optstring parameters   Examples     This is correct getopt  hv t     -v 123 -t123    getopt  hv t     -v123 -t123     -v and 123 doesn t have whitespace    -h takes no value  getopt  hv t     -h -v123      This is wrong  after -t can t have whitespace    Only optional params cannot have whitespace between key and value getopt  hv t     -v 123 -t 123     Multiple arguments that takes value  getopt  h v t  g     -h abc -v 123 -t21     Multiple arguments without value   All of these are correct getopt  hvt   -htv  getopt  hvt   -h -t -v  getopt  hvt   -tv -h    Here h v t are the options and -h -v -t is how options should be given in command-line     h  is a no-value option    v   implies that option -v has value and is a mandatory option      means has a value    t    implies that option -t has value but is optional       means optional    In optional param  value cannot have whitespace separation with the option  So  in  -t123  example  -t is option 123 is value   Syntax  Second Form  getopt  getopt options   --   optstring   parameters    Here after getopt is split into five parts   The command itself i e  getopt The getopt options  it describes how to parse the arguments  single dash long options  double dash options  --  separates out the getopt options from the options you want to parse and the allowed short options The short options  is taken immediately after -- is found  Just like the Form first syntax  The parameters  these are the options that you have passed into the program  The options you want to parse and get the actual values set on them    Examples  getopt -l  name  version   verbose  --  n v  V   --name Karthik -version 5 2 -verbose    Syntax  Third Form  getopt  getopt options   -o options   --   optstring   parameters    Here after getopt is split into five parts   The command itself i e  getopt The getopt options  it describes how to parse the arguments  single dash long options  double dash options  The short options i e  -o or --options  Just like the Form first syntax but with option  -o  and before the  --   double dash   --  separates out the getopt options from the options you want to parse and the allowed short options The parameters  these are the options that you have passed into the program  The options you want to parse and get the actual values set on them    Examples  getopt -l  name  version   verbose  -a -o  n v  V  --  -name Karthik -version 5 2 -verbose    GETOPT OPTIONS  getopt options changes the way command-line params are parsed   Below are some of the getopt options  Option  -l or --longoptions     Means getopt command should allow multi-character options to be   recognised  Multiple options are separated by comma    For example  --name Karthik is a long option sent in command line  In getopt  usage of long options are like  getopt  name  version   --name Karthik    Since name  is specified  the option should contain a value  Option  -a or --alternative     Means getopt command should allow long option to have a single dash    -  rather than double dash  --     Example  instead of --name Karthik you could use just -name Karthik  getopt  name  version   -name Karthik    A complete script example with the code      bin bash    filename  commandLine sh   author   theBuzzyCoder  showHelp        cat  lt  lt  EOF  This means that cat should stop reading when EOF is detected cat  lt  lt  EOF   Usage    installer -v  lt espo-version gt   -hrV  Install Pre-requisites for EspoCRM with docker in Development mode  -h  -help           --help                  Display help  -v  -espo-version   --espo-version          Set and Download specific version of EspoCRM  -r  -rebuild        --rebuild               Rebuild php vendor directory using composer and compiled css using grunt  -V  -verbose        --verbose               Run script in verbose mode  Will print out each step of execution   EOF   EOF is found above and hence cat command stops reading  This is equivalent to echo but much neater when printing out      export version 0 export verbose 0 export rebuilt 0       is all command line parameters passed to the script    -o is for short options like -v   -l is for long options with double dash like --version   the comma separates different long options   -a is for long options with single dash like -version options   getopt -l  help version  verbose rebuild dryrun  -o  hv Vrd  -a --          set --    If no arguments follow this option  then the positional parameters are unset  Otherwise  the positional parameters    are set to the arguments  even if some of them begin with a    -     eval set --   options   while true do case  1 in -h --help       showHelp     exit 0        -v --version       shift     export version  1        -V --verbose      export verbose 1     set -xv    Set xtrace and verbose mode         -r --rebuild      export rebuild 1        --      shift     break   esac shift done   Running this script file     With short options grouped together and long option   With double dash  --version   bash commandLine sh --version 1 0 -rV   With short options grouped together and long option   With single dash  -version   bash commandLine sh -version 1 0 -rV    OR with short option that takes value  value separated by whitespace   by key  bash commandLine sh -v 1 0 -rV    OR with short option that takes value  value without whitespace   separation from key   bash commandLine sh -v1 0 -rV    OR Separating individual short options  bash commandLine sh -v1 0 -r -V

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bin bash  usage     echo  Usage   0  -s  lt 45 90 gt    -p  lt string gt    1 gt  amp 2  exit 1     while getopts   s p   o  do     case    o   in         s              s   OPTARG                s    45    s    90      usage                        p              p   OPTARG                                        usage                    esac done shift    OPTIND-1    if   -z    s          -z    p      then     usage fi  echo  s     s   echo  p     p     Example runs       myscript sh Usage    myscript sh  -s  lt 45 90 gt    -p  lt string gt        myscript sh -h Usage    myscript sh  -s  lt 45 90 gt    -p  lt string gt        myscript sh -s    -p    Usage    myscript sh  -s  lt 45 90 gt    -p  lt string gt        myscript sh -s 10 -p foo Usage    myscript sh  -s  lt 45 90 gt    -p  lt string gt        myscript sh -s 45 -p foo s   45 p   foo      myscript sh -s 90 -p bar s   90 p   bar

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I know that this is already answered  but for the record and for anyone with the same requeriments as me I decided to post this related answer  The code is flooded with comments to explain the code   Updated answer   Save the file as getopt sh      bin bash  function get variable name for option       local OPT DESC   1      local OPTION   2      local VAR   echo   OPT DESC    sed -e  s       -  OPTION     A-Z          1 g  -e  s       -    OPTION       1FLAG g        if       VAR         1       then         echo        else         echo   VAR      fi    function parse options       local OPT DESC   1      local INPUT   get input for getopts    OPT DESC         shift     while getopts   INPUT  OPTION           do             OPTION            amp  amp  usage         VARNAME   get variable name for option    OPT DESC      OPTION                     VARNAME            amp  amp  eval    VARNAME    OPTARG -true      amp  amp  printf   t s n     Declaring   VARNAME     VARNAME  -- OPTIONS   OPTION       done      check for required    OPT DESC       function check for required       local OPT DESC   1      local REQUIRED   get required    OPT DESC     sed -e  s     g       while test -n    REQUIRED    do         OPTION   REQUIRED 0 1          VARNAME   get variable name for option    OPT DESC      OPTION                      -z     VARNAME      amp  amp  printf  ERROR   s n   Option -  OPTION  must been set    amp  amp  usage         REQUIRED   REQUIRED 1      done    function get input for getopts       local OPT DESC   1      echo   OPT DESC    sed -e  s    a-zA-Z     A-Z      1  g  -e  s     -   g     function get optional       local OPT DESC   1      echo   OPT DESC    sed -e  s                          1 g  -e  s    a-zA-Z     A-Z      1  g  -e  s     -   g     function get required       local OPT DESC   1      echo   OPT DESC    sed -e  s    a-zA-Z     A-Z      1  g  -e  s            g  -e  s     -   g     function usage       printf  Usage  n t s n     0    OPT DESC       exit 10     Then you can use it like this      bin bash       and   defines optional arguments      location to getopts sh file source   getopt sh USAGE  -u USER -d DATABASE -p PASS -s SID   -a START DATE TIME    parse options    USAGE         echo   USER  echo   START DATE TIME    Old answer   I recently needed to use a generic approach  I came across with this solution      bin bash   Option Description    -------------------     Option description is based on getopts bash builtin  The description adds a variable name feature to be used   on future checks for required or optional values    The option description adds    gt VARIABLE NAME  string  Variable name should be UPPERCASE  Valid characters   are  A-Z         A option description example      OPT DESC  a   gt A VARIABLE b   gt B VARIABLE c  gt C VARIABLE      -a option will require a value  the colon means that  and should be saved in variable A VARIABLE        is used to separate options description    -b option rule applies the same as -a    -c option doesn t require a value  the colon absense means that  and its existence should be set in C VARIABLE          echo get options   OPT DESC      a b c              Required options  REQUIRED DESC  a   gt REQ A VAR VALUE B   gt REQ B VAR VALUE c  gt REQ C VAR FLAG     Optional options  duh  OPTIONAL DESC  P   gt OPT P VAR VALUE r  gt OPT R VAR FLAG   function usage       IFS         printf   s    0      for i in   REQUIRED DESC       do         VARNAME   echo  i   sed -e  s     gt   g       printf    s   -  i 0 1   VARNAME      done      for i in   OPTIONAL DESC       do         VARNAME   echo  i   sed -e  s     gt   g           printf    s    -  i 0 1   VARNAME       done     printf   n      unset IFS     exit      Auxiliary function that returns options characters to be passed   into  getopts  from a option description    Arguments       1  The options description  SEE TOP      Example      OPT DESC  h   gt H VAR f   gt F VAR P  gt P VAR W  gt W VAR      OPTIONS   get options   OPT DESC       echo    OPTIONS       Output       h f PW  function get options       echo   1    sed -e  s    a-zA-Z         gt  A-Z        1 g       Auxiliary function that returns all variable names separated by       Arguments           1  The options description  SEE TOP      Example          OPT DESC  h   gt H VAR f   gt F VAR P  gt P VAR W  gt W VAR          VARNAMES   get values   OPT DESC           echo    VARNAMES       Output           H VAR F VAR P VAR W VAR  function get variables       echo   1    sed -e  s  a-zA-Z       gt            1 g       Auxiliary function that returns the variable name based on the   option passed by    Arguments       1  The options description  SEE TOP       2  The option which the variable name wants to be retrieved     Example      OPT DESC  h   gt H VAR f   gt F VAR P  gt P VAR W  gt W VAR      H VAR   get variable name   OPT DESC   h       echo    H VAR       Output       H VAR  function get variable name       VAR   echo   1    sed -e  s     2       gt              1 g       if      VAR       1      then         echo        else         echo   VAR      fi      Gets the required options from the required description REQUIRED   get options   REQUIRED DESC      Gets the optional options  duh  from the optional description OPTIONAL   get options   OPTIONAL DESC      or      get options    OPTIONAL DESC    REQUIRED DESC       The colon at starts instructs getopts to remain silent while getopts     REQUIRED   OPTIONAL   OPTION do          OPTION             amp  amp  usage     VAR   get variable name    REQUIRED DESC    OPTIONAL DESC     OPTION          -n   VAR      amp  amp  eval   VAR   OPTARG   done  shift     OPTIND - 1      Checks for required options  Report an error and exits if   required options are missing     Using function version     VARS   get variables   REQUIRED DESC   IFS     for VARNAME in  VARS  do        -v   VARNAME        usage done unset IFS        or using IFS Version  no function  OLDIFS   IFS  IFS     for i in   REQUIRED DESC   do     VARNAME   echo  i   sed -e  s     gt   g          -v   VARNAME        usage     printf   s  s  s n   -  i 0 1       VARNAME  present      VARNAME   done IFS   OLDIFS    I didn t test this roughly  so I could have some bugs in there

User · Answer

The example packaged with getopt  my distro put it in  usr share getopt getopt-parse bash  looks like it covers all of your cases      bin bash    A small example program for using the new getopt 1  program    This program will only work with bash 1    An similar program using the tcsh 1  script language can be found   as parse tcsh    Example input and output  from the bash prompt       parse bash -a par1  another arg  --c-long  wow      -cmore -b   very long     Option a   Option c  no argument   Option c  argument  more    Option b  argument   very long     Remaining arguments    -- gt   par1    -- gt   another arg    -- gt   wow         Note that we use        to let each command-line parameter expand to a    separate word  The quotes around      are essential    We need TEMP as the  eval set --  would nuke the return value of getopt  TEMP  getopt -o ab c   --long a-long b-long  c-long          -n  example bash  --        if         0     then echo  Terminating      gt  amp 2   exit 1   fi    Note the quotes around   TEMP   they are essential  eval set --   TEMP   while true   do     case   1  in         -a --a-long  echo  Option a    shift            -b --b-long  echo  Option b  argument    2     shift 2            -c --c-long                 c has an optional argument  As we are in quoted mode                an empty parameter will be generated if its optional               argument is not found              case   2  in                     echo  Option c  no argument   shift 2                        echo  Option c  argument    2     shift 2                esac            --  shift   break               echo  Internal error     exit 1        esac done echo  Remaining arguments   for arg do echo  -- gt       arg     done

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POSIX 7 example  It is also worth checking the example from the standard  http   pubs opengroup org onlinepubs 9699919799 utilities getopts html  aflag  bflag  while getopts ab  name do     case  name in     a     aflag 1       b     bflag 1           bval   OPTARG             printf  Usage   s   -a   -b value  args n   0           exit 2       esac done if     -z   aflag     then     printf  Option -a specified n  fi if     -z   bflag     then     printf  Option -b   s  specified n    bval  fi shift     OPTIND - 1   printf  Remaining arguments are   s n         And then we can try it out     sh a sh Remaining arguments are     sh a sh -a Option -a specified Remaining arguments are     sh a sh -b No arg for -b option Usage  a sh   -a   -b value  args   sh a sh -b myval Option -b  myval  specified Remaining arguments are     sh a sh -a -b myval Option -a specified Option -b  myval  specified Remaining arguments are     sh a sh remain Remaining arguments are  remain   sh a sh -- -a remain Remaining arguments are  -a remain   Tested in Ubuntu 17 10  sh is dash 0 5 8

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