Read a variable in bash with a default value

问题:

I need to read a value from the terminal in a bash script. I would like to be able to provide a default value that the user can change.

# Please enter your name: Ricardo^

In this script the prompt is "Please enter your name: " the default value is "Ricardo" and the cursor would be after the default value. Is there a way to do this in a bash script?

回答1:

you can use parameter expansion eg

read -p "Enter: " name
name=${name:-Richard}
echo $name

回答2:

read -e -p "Enter Your Name:" -i "Ricardo" NAME

echo $NAME

回答3:

In Bash 4:

name="Ricardo"
read -e -i "$name" -p "Please enter your name: " input
name="${input:-$name}"

This displays the name after the prompt like this:

Please enter your name: Ricardo

with the cursor at the end of the name and allows the user to edit it. The last line is optional and forces the name to be the original default if the user erases the input or default (submitting a null).

回答4:

Code:

IN_PATH_DEFAULT="/tmp/input.txt"
read -p "Please enter IN_PATH [$IN_PATH_DEFAULT]: " IN_PATH
IN_PATH="${IN_PATH:-$IN_PATH_DEFAULT}"

OUT_PATH_DEFAULT="/tmp/output.txt"
read -p "Please enter OUT_PATH [$OUT_PATH_DEFAULT]: " OUT_PATH
OUT_PATH="${OUT_PATH:-$OUT_PATH_DEFAULT}"

echo "Input: $IN_PATH Output: $OUT_PATH"

Sample run:

Please enter IN_PATH [/tmp/input.txt]: 
Please enter OUT_PATH [/tmp/output.txt]: ~/out.txt
Input: /tmp/input.txt Output: ~/out.txt

回答5:

I found this question, looking for a way to present something like:

Something interesting happened.  Proceed [Y/n/q]:

Using the above examples I deduced this:-

echo -n "Something interesting happened.  "
DEFAULT="y"
read -e -p "Proceed [Y/n/q]:" PROCEED
# adopt the default, if 'enter' given
PROCEED="${PROCEED:-${DEFAULT}}"
# change to lower case to simplify following if
PROCEED="${PROCEED,,}"
# condition for specific letter
if [ "${PROCEED}" == "q" ] ; then
  echo "Quitting"
  exit
# condition for non specific letter (ie anything other than q/y)
# if you want to have the active 'y' code in the last section
elif [ "${PROCEED}" != "y" ] ; then
  echo "Not Proceeding"
else
  echo "Proceeding"
  # do proceeding code in here
fi

Hope that helps someone to not have to think out the logic, if they encounter the same problem

回答6:

I've just used this pattern, which I prefer:

read name || name='(nobody)'

回答7:

name=Ricardo
echo "Please enter your name: $name \c"
read newname
[ -n "$newname" ] && name=$newname

Set the default; print it; read a new value; if there is a new value, use it in place of the default. There is (or was) some variations between shells and systems on how to suppress a newline at the end of a prompt. The '\c' notation seems to work on MacOS X 10.6.3 with a 3.x bash, and works on most variants of Unix derived from System V, using Bourne or Korn shells.

Also note that the user would probably not realize what is going on behind the scenes; their new data would be entered after the name already on the screen. It might be better to format it:

echo "Please enter your name ($name): \c"

回答8:

#Script for calculating various values in MB
echo "Please enter some input: "
read input_variable
echo $input_variable | awk '{ foo = $1 / 1024 / 1024 ; print foo "MB" }'

回答9:

The -e and -t parameter does not work together. i tried some expressions and the result was the following code snippet :

QMESSAGE="SHOULD I DO YES OR NO"
YMESSAGE="I DO"
NMESSAGE="I DO NOT"
FMESSAGE="PLEASE ENTER Y or N"
COUNTDOWN=2
DEFAULTVALUE=n
#----------------------------------------------------------------#
function REQUEST ()
{
read -n1 -t$COUNTDOWN -p "$QMESSAGE ? Y/N " INPUT
    INPUT=${INPUT:-$DEFAULTVALUE}
    if  [ "$INPUT" = "y" -o "$INPUT" = "Y" ] ;then
        echo -e "\n$YMESSAGE\n"
        #COMMANDEXECUTION
    elif    [ "$INPUT" = "n" -o "$INPUT" = "N" ] ;then
        echo -e "\n$NMESSAGE\n"
        #COMMANDEXECUTION
    else
        echo -e "\n$FMESSAGE\n"
    REQUEST
    fi
}
REQUEST