In Bash how to add Are you sure Y n to any command or alias

Question

In this particular case  I d like to add a confirm in Bash for   Are you sure   Y n    for Mercurial s hg push ssh   username www example com  somepath morepath  which is actually an alias   Is there a standard command that can be added to the alias to achieve it   The reason is that hg push and hg out can sound similar and sometimes when I want hgoutrepo  I may accidentlly type hgpushrepo  both are aliases    Update  if it can be something like a built-in command with another command  such as  confirm  amp  amp  hg push ssh       that d be great    just a command that can ask for a yes or no and continue with the rest if yes

User · Accepted Answer

These are more compact and versatile forms of Hamish's answer. They handle any mixture of upper and lower case letters:

read -r -p "Are you sure? [y/N] " response
case "$response" in
    [yY][eE][sS]|[yY]) 
        do_something
        ;;
    *)
        do_something_else
        ;;
esac

Or, for Bash >= version 3.2:

read -r -p "Are you sure? [y/N] " response
if [[ "$response" =~ ^([yY][eE][sS]|[yY])$ ]]
then
    do_something
else
    do_something_else
fi

Note: If $response is an empty string, it will give an error. To fix, simply add quotation marks: "$response". – Always use double quotes in variables containing strings (e.g.: prefer to use "$@" instead $@).

Or, Bash 4.x:

read -r -p "Are you sure? [y/N] " response
response=${response,,}    # tolower
if [[ "$response" =~ ^(yes|y)$ ]]
...

Edit:

In response to your edit, here's how you'd create and use a confirm command based on the first version in my answer (it would work similarly with the other two):

confirm() {
    # call with a prompt string or use a default
    read -r -p "${1:-Are you sure? [y/N]} " response
    case "$response" in
        [yY][eE][sS]|[yY]) 
            true
            ;;
        *)
            false
            ;;
    esac
}

To use this function:

confirm && hg push ssh://..

or

confirm "Would you really like to do a push?" && hg push ssh://..

User · Answer

This may be a hack   as in question In Unix   Bash  is  quot xargs -p quot  a good way to prompt for confirmation before running any command   we can using xargs to do the job   echo ssh   username www example com  somepath morepath   xargs -p hg push   of course  this will be set as an alias  like  hgpushrepo  Example     echo foo   xargs -p ls -l ls -l foo    y -rw-r--r--  1 mikelee    staff  0 Nov 23 10 38 foo    echo foo   xargs -p ls -l ls -l foo    n

User · Answer

To avoid explicitly checking for these variants of  yes  you could use the bash regular expression operator      with a regular expression   read -p  Are you sure you want to continue   lt y N gt    prompt if     prompt     yY  es      then  etc       That tests whether the user input starts with  y  or  Y  and is followed by zero or more  es s

User · Answer

No pressing enter required Here s a longer  but reusable and modular approach   Returns 0 yes and 1 no No pressing enter required - just a single character Can press enter to accept the default choice Can disable default choice to force a selection Works for both zsh and bash   Defaulting to  quot no quot  when pressing enter Note that the N is capitalsed  Here enter is pressed  accepting the default    confirm  quot Show dangerous command quot   amp  amp  echo  quot rm   quot  Show dangerous command  y N    Also note  that   y N   was automatically appended  The default  quot no quot  is accepted  so nothing is echoed  Re-prompt until a valid response is given    confirm  quot Show dangerous command quot   amp  amp  echo  quot rm   quot  Show dangerous command  y N   X Show dangerous command  y N   y rm    Defaulting to  quot yes quot  when pressing enter Note that the Y is capitalised    confirm yes  quot Show dangerous command quot   amp  amp  echo  quot rm   quot  Show dangerous command  Y n   rm    Above  I just pressed enter  so the command ran  No default on enter - require y or n   get yes keypress  quot Here you cannot press enter  Do you like this quot  Here you cannot press enter  Do you like this  y n   k Here you cannot press enter  Do you like this  y n   Here you cannot press enter  Do you like this  y n   n   echo    1  Here  1 or false was returned  Note no capitalisation in  y n   Code   Read a single char from  dev tty  prompting with  quot    quot    Note  pressing enter will return a null string  Perhaps a version terminated with X and then remove it in caller    See https   unix stackexchange com a 367880 143394 for dealing with multi-byte  etc  function get keypress     local REPLY IFS     gt  dev tty printf   s   quot    quot        ZSH VERSION     amp  amp  read -rk1    Use -u0 to read from STDIN     See https   unix stackexchange com q 383197 143394 regarding   n  - gt           BASH VERSION     amp  amp   lt  dev tty read -rn1   printf   s   quot  REPLY quot       Get a y n from the user  return yes 0  no 1 enter  2   Prompt using  1    If set  return  2 on pressing enter  useful for cancel or defualting function get yes keypress     local prompt  quot   1 -Are you sure   y n    quot    local enter return  2   local REPLY           prompt     amp  amp  prompt  quot  y n    quot    while REPLY   get keypress  quot  prompt quot    do         REPLY     amp  amp  printf   n     REPLY blank if user presses enter     case  quot  REPLY quot  in       Y y   return 0         N n   return 1                   enter return     amp  amp  return  quot  enter return quot      esac   done          Credit  http   unix stackexchange com a 14444 143394   Prompt to confirm  defaulting to NO on  lt enter gt    Usage  confirm  quot Dangerous  Are you sure  quot   amp  amp  rm   function confirm     local prompt  quot     -Are you sure   y N    quot    get yes keypress  quot  prompt quot  1          Prompt to confirm  defaulting to YES on  lt enter gt  function confirm yes     local prompt  quot     -Are you sure   Y n    quot    get yes keypress  quot  prompt quot  0

User · Answer

This may be a little too short  but for my own private use  it works great  read -n 1 -p  Push master upstream   Y n    reply   if     reply           then echo  fi if     reply       reply  Nn       then     git push upstream master fi   The read -n 1 just reads one character  No need to hit enter  If it s not a  n  or  N   it is assumed to be a  Y   Just pressing enter means Y too    as for the real question  make that a bash script and change your alias to point to that script instead of what is was pointing to before

User · Answer

Not the same  but idea that works anyway      bin bash   i  y    while     i 0 1     n     do         Command s        read -p   Again  Y n   i             i  -eq 0     amp  amp  i  y    done     Output       Again  Y n N      Again  Y n Anything      Again  Y n 7      Again  Y n  amp       Again  Y n nsijf      Now only checks 1st character of  i read

User · Answer

Here is roughly a snippet that you want  Let me find out how to forward the arguments   read -p  Are you sure you want to continue   lt y N gt    prompt if     prompt     y      prompt     Y      prompt     yes      prompt     Yes     then     http   stackoverflow com questions 1537673 how-do-i-forward-parameters-to-other-command-in-bash-script else   exit 0 fi   Watch out for yes   command name here

User · Answer

Add the following to your  etc bashrc file  This script adds a resident  function  instead of an alias called  confirm      function confirm       alert the user what they are about to do  echo  About to           confirm with the user read -r -p  Are you sure   Y n   response case   response  in      yY  eE  sS   yY                   if yes  then execute the passed parameters                                                             Otherwise exit                  echo  ciao                   exit                  esac

User · Answer

Below code is combining two things   shopt -s nocasematch that will take care of case insensitive and if condition that will accept both the input either you pass yes Yes YES y   shopt -s nocasematch  if    sed-4 2 2  LINE     yes y       then exit 0   fi

User · Answer

This version allows you to have more than one case y or Y  n or N   Optionally  Repeat the question until an approve question is provided Optionally  Ignore any other answer Optionally  Exit the terminal if you want  confirm         echo -n  Continue  y or n        read REPLY     case  REPLY in      Yy   echo  yup y       you can change what you do here for instance      Nn   break             exit case statement gracefully       Here are a few optional options to choose between       Any other answer         1  Repeat the question        confirm           2  ignore                    3  Exit terminal          exit         esac       REPLY         Notice this too  On the last line of this function clear the REPLY variable  Otherwise if you echo  REPLY you will see it is still set until you open or close your terminal or set it again

User · Answer

Well  here s my version of confirm  modified from James  one   function confirm       local response msg    1 -Are you sure   y  n       shift   read -r    -p   msg  response    echo   case   response  in    yY  eE  sS   yY   return 0         return 1      esac     These changes are    use local to prevent variable names from colliding read use  2  3     to control its action  so you may use -n and -t if read exits unsuccessfully  echo a line feed for beauty my Git on Windows only has bash-3 1 and has no true or false  so use return instead  Of course  this is also compatible with bash-4 4  the current one in Git for Windows   use IPython-style   y  n    to clearly indicate that  n  is the default

User · Answer

Try       bin bash  pause        REPLY Y  while     REPLY      Y           REPLY      y     do   echo -e   t tPress  y  to continue t t tPress  n  to quit    read -n1 -s       case   REPLY  in        n    exit                                N    echo  case sensitive                 y    clear                               Y    echo  case sensitive                    echo   REPLY is Invalid Option          esac  done     pause  echo  Hi

User · Answer

read -r -p  Are you sure   Y n   response   response   response      tolower   if     response      yes y             -z  response     then       your-action-here   fi

User · Answer

Confirmations are easily bypassed with carriage returns  and I find it useful to continually prompt for valid input   Here s a function to make this easy   invalid input  appears in red if Y N is not received  and the user is prompted again   prompt confirm       while true  do     read -r -n 1 -p    1 -Continue    y n     REPLY     case  REPLY in        yY   echo   return 0           nN   echo   return 1             printf    033 31m  s  n 033 0m   invalid input      esac    done        example usage prompt confirm  Overwrite File      exit 0   You can change the default prompt by passing an argument

User · Answer

Late to the game  but I created yet another variant of the confirm functions of previous answers   confirm          read -r -p    echo        y N    YESNO      if     YESNO      y     then         echo  gt  amp 2  Aborting          exit 1     fi      CMD   1      shift      while   -n   1     do         echo -en   1 0          shift     done   xargs -0   CMD     exit        To use it   confirm your command   Features    prints your command as part of the prompt passes arguments through using the NULL delimiter preserves your command s exit state   Bugs    echo -en works with bash but might fail in your shell might fail if arguments interfere with echo or xargs a zillion other bugs because shell scripting is hard

User · Answer

Here is my solution that using localised regex  So in german also  j  for  Ja  would be interpreted as yes   First argument is the question  if the second argument is  y  than yes would be the default answer otherwise no would be the default answer  The return value is 0 if the answer was  yes  and 1 if the answer was  no    function shure        if      -gt 1    amp  amp       2       yY         then         arg   Y n           reg   locale noexpr          default  0 1      else         arg   y N           reg   locale yesexpr          default  1 0      fi     read -p   1   arg       answer          answer      reg     amp  amp  return   default 1      return   default 0       Here is a basic usage    basic example default is no shure  question message   amp  amp  echo  answer yes     echo  answer no    print  question message  y N          basic example default set to yes shure  question message  y  amp  amp  echo  answer yes     echo  answer no    print  question message  Y n

User · Answer

This isn t exactly an  asking for yes or no  but just a hack  alias the hg push     not to hgpushrepo but to hgpushrepoconfirmedpush and by the time I can spell out the whole thing  the left brain has made a logical choice

User · Answer

I know this is an old question but this might help someone  it hasn t been addressed here  I have been asked how to use rm -i in a script which is receiving input from a file  As file input to a script is normally received from STDIN we need to change it  so that only the response to the rm command is received from STDIN  Here s the solution     bin bash while read -u 3 line do  echo -n  quot Remove file  line  quot   read -u 1 -n 1 key      key    quot y quot      amp  amp   rm  quot  line quot   echo done 3 lt filelist  If ANY key other than the  quot y quot  key  lower case only  is pressed  the file will not be deleted  It is not necessary to press return after the key  hence the echo command to send a new line to the display   Note that the POSIX bash  quot read quot  command does not support the -u switch so a workaround would need to be sought

[bash] In Bash, how to add "Are you sure [Y/n]" to any command or alias?

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