Bash Shell Script - Check for a flag and grab its value

Question

I am trying to make a shell script which is designed to be run like this   script sh -t application   Firstly  in my script I want to check to see if the script has been run with the -t flag  For example if it has been run without the flag like this I want it to error   script sh   Secondly  assuming there is a -t flag  I want to grab the value and store it in a variable that I can use in my script for example like this   FLAG  application    So far the only progress I ve been able to make on any of this is that    grabs all the command line arguments but I don t know how this relates to flags  or if this is even possible

User · Answer

Use    to grab the number of arguments  if it is unequal to 2 there are not enough arguments provided   if      -ne 2    then    usage  fi   Next  check if  1 equals -t  otherwise an unknown flag was used   if     1      -t     then   usage  fi   Finally store  2 in FLAG   FLAG  2   Note  usage   is some function showing the syntax  For example   function usage      cat  lt  lt  EOF Usage  script sh -t  lt application gt   Performs some activity EOF    exit 1

User · Answer

Try shFlags -- Advanced command-line flag library for Unix shell scripts   http   code google com p shflags   It is very good and very flexible    FLAG TYPES  This is a list of the DEFINE   s that you can do   All flags take   a name  default value  help-string  and optional  short  name  one-letter   name    Some flags have other arguments  which are described with the flag   DEFINE string  takes any input  and intreprets it as a string   DEFINE boolean  typically does not take any argument  say --myflag to set     FLAGS myflag to true  or --nomyflag to set FLAGS myflag to false      Alternately  you can say       --myflag true  or --myflag t or --myflag 0  or       --myflag false or --myflag f or --myflag 1     Passing an option has the same affect as passing the option once   DEFINE float  takes an input and intreprets it as a floating point number  As     shell does not support floats per-se  the input is merely validated as     being a valid floating point value   DEFINE integer  takes an input and intreprets it as an integer   SPECIAL FLAGS  There are a few flags that have special meaning      --help  or -    prints a list of all the flags in a human-readable fashion     --flagfile foo  read flags from foo    not implemented yet      --              as in getopt    terminates flag-processing  EXAMPLE USAGE   -- begin hello sh --     bin sh     shflags DEFINE string name  world   somebody s name  n FLAGS         exit    eval set --    FLAGS ARGV   echo  Hello    FLAGS name    -- end hello sh --      hello sh -n Kate Hello  Kate    Note  I took this text from shflags documentation

User · Answer

Here is a generalized simple command argument interface you can paste to the top of all your scripts      bin bash  declare -A flags declare -A booleans args     while     1     do     arg  1     if      1 0 1       -        then       shift       rev   echo   arg    rev        if   -z   1            1 0 1       -            rev 0 1                  then         bool   echo   arg 1    sed s    g          booleans  bool  true         echo    bool   is boolean       else         value  1         flags   arg 1    value         shift         echo    arg   is flag with value    value         fi     else       args     arg         shift       echo    arg   is an arg     fi done   echo -e   n  echo booleans    booleans     echo flags    flags     echo args    args      echo -e   nBoolean types  n tPrecedes Flag pf     booleans pf   n tFinal Arg f     booleans f   n tColon Terminated Ct     booleans Ct   n tNot Mentioned nm     boolean nm    echo -e   nFlag  myFlag   gt    flags  myFlag     echo -e   nArgs  one    args 0    two    args 1    three    args 2      By running the command   bashScript sh firstArg -pf -myFlag  my flag value  secondArg -Ct  thirdArg -f   The output will be this    firstArg  is an arg  pf  is boolean  -myFlag  is flag with value  my flag value   secondArg  is an arg  Ct  is boolean  thirdArg  is an arg  f  is boolean   booleans  true true true flags  my flag value args  firstArg secondArg thirdArg  Boolean types      Precedes Flag pf   true     Final Arg f   true     Colon Terminated Ct   true     Not Mentioned nm     Flag  myFlag   gt  my flag value  Args  one   gt  firstArg  two   gt  secondArg  three   gt  thirdArg   Basically  the arguments are divided up into flags booleans and generic arguments  By doing it this way a user can put the flags and booleans anywhere as long as he she keeps the generic arguments  if there are any  in the specified order    Allowing me and now you to never deal with bash argument parsing again   You can view an updated script here  This has been enormously useful over the last year  It can now simulate scope by prefixing the variables with a scope parameter   Just call the script like  replace       source  FUTIL REL DIR commandParser sh -scope   FUNCNAME 0          echo   replaceFlags f     echo   replaceBooleans b       Doesn t look like I implemented argument scope  not sure why I guess I haven t needed it yet

User · Answer

You should read this getopts tutorial   Example with -a switch that requires an argument       bin bash  while getopts   a   opt  do   case  opt in     a        echo  -a was triggered  Parameter   OPTARG   gt  amp 2                        echo  Invalid option  - OPTARG   gt  amp 2       exit 1                       echo  Option - OPTARG requires an argument    gt  amp 2       exit 1            esac done   Like greybot said getopt    getopts         The external command getopt 1  is never safe to use  unless you know   it is GNU getopt  you call it in a GNU-specific way  and you ensure   that GETOPT COMPATIBLE is not in the environment  Use getopts  shell   builtin  instead  or simply loop over the positional parameters

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