在bash中读取具有默认值的变量

你可以用 parameter expansion

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

在括号之间的提示中包含默认值是一种相当常见的约定

这是什么意思 :-Richard 你要做什么?从bash手册:

${parameter:-word}

同样值得注意的是。。。

在下面的每种情况下,word都要进行波浪号扩展、参数扩展、命令替换和算术扩展。

所以如果你用 webpath=${webpath:-~/httpdocs} /home/user/expanded/path/httpdocs 不 ~/httpdocs

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

echo $NAME

在Bash 4中:

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

这将在提示符后显示名称,如下所示:

Please enter your name: Ricardo

我发现了这个问题,想用一种方式来表达:

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

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

代码:

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"

运行示例:

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

我刚用了这个模式,我更喜欢:

read name || name='(nobody)'

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

设置默认值;打印出来;读取新值;如果有新值,请使用它来代替默认值。shell和系统之间存在(或曾经存在)一些关于如何在提示符末尾禁止换行的变体。“\c”符号似乎适用于带有3.xbash的macosx10.6.3,并且适用于大多数从systemv派生的Unix变体,使用Bourne或Korn shell。

还要注意的是,用户可能不会意识到幕后发生了什么;他们的新数据将在屏幕上已有的名称之后输入。最好将其格式化:

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

#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" }'

-e和-t参数不能一起工作。我尝试了一些表达式,结果得到以下代码段:

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