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://[email protected]//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 & hg push ssh://... that'd be great... just 1 command that ask for a yes and continue with the rest if so.

Answer 1

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? <y/N> " 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 :)

Answer 2

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? <y/N> " 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.

Answer 3

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

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://..

Answer 4

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
}

Answer 5

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.

Answer 6

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

# if only press Enter we need detect this condiction

Answer 7

This may be a hack:

as in question http://stackoverflow.com/questions/3400799/is-xargs-p-a-good-way-to-prompt-for-confirmation-before-running-any-command-on

we can

echo ssh://[email protected]//somepath/morepath | xargs -p hg push

of course, this will be set as an alias, like hgpushrepo