How to get arguments with flags in Bash

Question

I know that I can easily get positioned parameters like this in bash    0 or  1  I want to be able to use flag options like this to specify for what each parameter is used   mysql -u user -h host   What is the best way to get -u param value and -h param value by flag instead of by position

User · Answer

I think this would serve as a simpler example of what you want to achieve. There is no need to use external tools. Bash built in tools can do the job for you.

function DOSOMETHING {

   while test $# -gt 0; do
           case "$1" in
                -first)
                    shift
                    first_argument=$1
                    shift
                    ;;
                -last)
                    shift
                    last_argument=$1
                    shift
                    ;;
                *)
                   echo "$1 is not a recognized flag!"
                   return 1;
                   ;;
          esac
  done  

  echo "First argument : $first_argument";
  echo "Last argument : $last_argument";
 }

This will allow you to use flags so no matter which order you are passing the parameters you will get the proper behavior.

Example :

 DOSOMETHING -last "Adios" -first "Hola"

Output :

 First argument : Hola
 Last argument : Adios

You can add this function to your profile or put it inside of a script.

Thanks!

Edit : Save this as a a file and then execute it as yourfile.sh -last "Adios" -first "Hola"

#!/bin/bash
while test $# -gt 0; do
           case "$1" in
                -first)
                    shift
                    first_argument=$1
                    shift
                    ;;
                -last)
                    shift
                    last_argument=$1
                    shift
                    ;;
                *)
                   echo "$1 is not a recognized flag!"
                   return 1;
                   ;;
          esac
  done  

  echo "First argument : $first_argument";
  echo "Last argument : $last_argument";

User · Answer

If you re familiar with Python argparse  and don t mind calling python to parse bash arguments  there is a piece of code I found really helpful and super easy to use called argparse-bash https   github com nhoffman argparse-bash  Example take from their example sh script      bin bash  source   dirname  0  argparse bash    exit 1 argparse       lt  lt EOF    exit 1 parser add argument  infile   parser add argument  outfile   parser add argument  -a    --the-answer   default 42  type int                      help  Pick a number  default   default s    parser add argument  -d    --do-the-thing   action  store true                       default False  help  store a boolean  default   default s    parser add argument  -m    --multiple   nargs                          help  multiple values allowed   EOF  echo required infile    INFILE  echo required outfile    OUTFILE  echo the answer    THE ANSWER  echo -n do the thing  if     DO THE THING     then     echo   yes  do it  else     echo   no  do not do it  fi echo -n  arg with multiple values    for a in    MULTIPLE       do     echo -n    a    done echo

User · Answer

I propose a simple TLDR   example for the un-initiated   Create a bash script called helloworld sh     bin bash  while getopts  n   arg  do   case  arg in     n  Name  OPTARG     esac done  echo  Hello  Name     You can then pass an optional parameter -n when executing the script   Execute the script as such     bash helloworld sh -n  World    Output    Hello World    Notes  If you d like to use multiple parameters    extend while getops  n   arg  do with more paramaters such as while getops  n o p   arg  do extend the case switch with extra variable assignments  Such as o  Option  OPTARG and p  Parameter  OPTARG

User · Answer

This example uses Bash s built-in getopts command and is from the Google Shell Style Guide   a flag    b flag    files    verbose  false   print usage       printf  Usage          while getopts  abf v  flag  do   case    flag   in     a  a flag  true         b  b flag  true         f  files    OPTARG          v  verbose  true            print usage        exit 1      esac done   Note  If a character is followed by a colon  e g  f    that option is expected to have an argument   Example usage    script -v -a -b -f filename  Using getopts has several advantages over the accepted answer    the while condition is a lot more readable and shows what the accepted options are cleaner code  no counting the number of parameters and shifting you can join options  e g  -a -b -c   -abc    However  a big disadvantage is that it doesn t support long options  only single-character options

User · Answer

I like Robert McMahan s answer the best here as it seems the easiest to make into sharable include files for any of your scripts to use   But it seems to have a flaw with the line if    -n   variables  argument label      throwing the message   variables  bad array subscript    I don t have the rep to comment  and I doubt this is the proper  fix   but wrapping that if in if    -n  argument label      then cleans it up   Here s the code I ended up with  if you know a better way please add a comment to Robert s answer   Include File  flags-declares sh     declaring a couple of associative arrays declare -A arguments     declare -A variables        declaring an index integer declare -i index 1    Include File  flags-arguments sh        here represents all arguments passed in for i in      do   arguments  index   i    prev index    expr  index - 1         this if block does something akin to  where  i contains              here strips out everything from the   to the end of the argument leaving only the label   if     i                 then argument label   i         else argument label   arguments  prev index     fi    if    -n  argument label      then       this if block only evaluates to true if the argument label exists in the variables array     if    -n   variables  argument label        then         dynamically creating variables names using declare            argument label   here strips out the label leaving only the value       if     i                     then declare   variables  argument label     i  argument label            else declare   variables  argument label     arguments  index         fi     fi   fi    index index 1  done    Your  script sh     bin includes flags-declares sh    any variables you want to use here   on the left left side is argument label or key  entered at the command line along with it s value     on the right side is the variable name the value of these arguments should be mapped to     the examples above show how these are being passed into this script  variables  -gu    git user   variables  --git-user    git user   variables  -gb    git branch   variables  --git-branch    git branch   variables  -dbr    db fqdn   variables  --db-redirect    db fqdn   variables  -e    environment   variables  --environment    environment      bin includes flags-arguments sh    then you could simply use the variables like so  echo   git user   echo   git branch   echo   db fqdn   echo   environment

User · Answer

getopt is your friend   a simple example   function f      TEMP  getopt --long -o  u h         eval set --   TEMP  while true   do     case   1  in         -u               user  2             shift 2                    -h               host  2             shift 2                                   break                esac  done   echo  user    user  host    host     f -u myself -h some host   There should be various examples in your  usr bin directory

User · Answer

So here it is my solution  I wanted to be able to handle boolean flags without hyphen  with one hyphen  and with two hyphen as well as parameter value assignment with one and two hyphens     Handle multiple types of arguments and prints some variables     Boolean flags   1  No hyphen      create   Assigns  true  to the variable  CREATE                 Default is  CREATE DEFAULT        delete   Assigns true to the variable  DELETE                 Default is  DELETE DEFAULT     2  One hyphen        a      Assigns  true  to a  Default is  false          b      Assigns  true  to b  Default is  false     3  Two hyphens      cats     Assigns  true  to  cats   By default is not set       dogs     Assigns  true  to  cats   By default is not set      Parameter - Value   1  One hyphen        c      Assign any value you want        d      Assign any value you want     2  Two hyphens         Anything really  whatever two-hyphen argument is given that is not         defined as flag  will be defined with the next argument after it      Example      parser example sh delete -a -c VA 1 --cats --dir  path to dir parser           Define arguments with one hyphen that are boolean flags     HYPHEN FLAGS  a b        Define arguments with two hyphens that are boolean flags     DHYPHEN FLAGS  cats dogs         Iterate over all the arguments     while      -gt 0    do           Handle the arguments with no hyphen         if     1     -       then             echo  Argument with no hyphen               echo  1               Assign true to argument  1             declare  1 true               Shift arguments by one to the left             shift           Handle the arguments with one hyphen         elif     1     -  A-Za-z0-9       then               Handle the flags             if     HYPHEN FLAGS        1 -         then                 echo  Argument with one hyphen flag                   echo  1                   Remove the hyphen from  1                 local param    1 -                      Assign true to  param                 declare  param true                   Shift by one                 shift               Handle the parameter-value cases             else                 echo  Argument with one hyphen value                   echo  1  2                   Remove the hyphen from  1                 local param    1 -                      Assign argument  2 to  param                 declare  param   2                    Shift by two                 shift 2             fi           Handle the arguments with two hyphens         elif     1     --  A-Za-z0-9       then               NOTE  For double hyphen I am using  declare -g  param                   This is the case because I am assuming that s going to be                 the final name of the variable             echo  Argument with two hypens                 Handle the flags             if     DHYPHEN FLAGS        1 --         then                 echo  1 true                   Remove the hyphens from  1                 local param    1 --                      Assign argument  2 to  param                 declare -g  param true                   Shift by two                 shift               Handle the parameter-value cases             else                 echo  1  2                   Remove the hyphens from  1                 local param    1 --                      Assign argument  2 to  param                 declare -g  param   2                    Shift by two                 shift 2             fi         fi      done       Default value for arguments with no hypheb     CREATE   create - CREATE DEFAULT       DELETE   delete - DELETE DEFAULT         Default value for arguments with one hypen flag     VAR1   a -false      VAR2   b -false        Default value for arguments with value       NOTE1  This is just for illustration in one line  We can well create         another function to handle this  Here I am handling the cases where         we have a full named argument and a contraction of it          For example  --arg1  can be also set with  -c         NOTE2  What we are doing here is to check if  arg is defined  If not          check if  c was defined  If not  assign the default value  VD       VAR3   if     arg1     then echo  arg1  else echo   c - VD 1    fi      VAR4   if     arg2     then echo  arg2  else echo   d - VD 2    fi        Pass all the arguments given to the script to the parser function parser        echo  CREATE  DELETE  VAR1  VAR2  VAR3  VAR4  cats  dir   Some references   The main procedure was found here  More about passing all the arguments to a function here  More info regarding default values here  More info about declare do   bash -c  help declare   More info about shift do   bash -c  help shift

User · Answer

This is the idiom I usually use   while test    -gt 0  do   case   1  in     -h --help        echo   package - attempt to capture frames        echo           echo   package  options  application  arguments         echo           echo  options         echo  -h  --help                show brief help        echo  -a  --action ACTION       specify an action to use        echo  -o  --output-dir DIR      specify a directory to store output in        exit 0              -a        shift       if test    -gt 0  then         export PROCESS  1       else         echo  no process specified          exit 1       fi       shift              --action         export PROCESS  echo  1   sed -e  s          g         shift              -o        shift       if test    -gt 0  then         export OUTPUT  1       else         echo  no output dir specified          exit 1       fi       shift              --output-dir         export OUTPUT  echo  1   sed -e  s          g         shift                       break            esac done   Key points are       is the number of arguments while loop looks at all the arguments supplied  matching on their values inside a case statement shift takes the first one away  You can shift multiple times inside of a case statement to take multiple values

User · Answer

Another alternative would be to use something like the below example which would allow you to use long --image or short -i tags and also allow compiled -i  example jpg  or separate -i example jpg methods of passing in arguments     declaring a couple of associative arrays declare -A arguments       declare -A variables        declaring an index integer declare -i index 1     any variables you want to use here   on the left left side is argument label or key  entered at the command line along with it s value     on the right side is the variable name the value of these arguments should be mapped to     the examples above show how these are being passed into this script  variables  -gu    git user     variables  --git-user    git user     variables  -gb    git branch     variables  --git-branch    git branch     variables  -dbr    db fqdn     variables  --db-redirect    db fqdn     variables  -e    environment     variables  --environment    environment         here represents all arguments passed in for i in        do     arguments  index   i    prev index    expr  index - 1         this if block does something akin to  where  i contains              here strips out everything from the   to the end of the argument leaving only the label   if     i                 then argument label   i          else argument label   arguments  prev index     fi      this if block only evaluates to true if the argument label exists in the variables array   if    -n   variables  argument label          then           dynamically creating variables names using declare              argument label   here strips out the label leaving only the value         if     i                         then declare   variables  argument label     i  argument label                else declare   variables  argument label     arguments  index           fi   fi    index index 1  done     then you could simply use the variables like so  echo   git user

User · Answer

bin bash  if getopts  n   arg  then   echo  Welcome  OPTARG  fi   Save it as sample sh and try running  sh sample sh -n John   in your terminal

User · Answer

I had trouble using getopts with multiple flags  so I wrote this code   It uses a modal variable to detect flags  and to use those flags to assign arguments to variables   Note that  if a flag shouldn t have an argument  something other than setting CURRENTFLAG can be done       for MYFIELD in       do          CHECKFIRST  echo  MYFIELD   cut -c1           if     CHECKFIRST      -     then             mode  flag          else             mode  arg          fi          if     mode      flag     then             case  MYFIELD in                 -a                      CURRENTFLAG  VARIABLE A                                         -b                      CURRENTFLAG  VARIABLE B                                         -c                      CURRENTFLAG  VARIABLE C                                     esac         elif     mode      arg     then             case  CURRENTFLAG in                 VARIABLE A                      VARIABLE A   MYFIELD                                         VARIABLE B                      VARIABLE B   MYFIELD                                         VARIABLE C                      VARIABLE C   MYFIELD                                     esac         fi     done

[bash] How to get arguments with flags in Bash

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