bash中的正则表达式不一致

Question

我试图自学bash脚本，并且我试图学习如何在复合测试命令（[[]]）和测试（[]）之间交替。

使用我从中学习的书，我尝试使用test而不是[[]]重新创建以下程序。

#!/bin/bash

# read-validate: valiate input

invalid_input()
{
    echo "Invalid input '$REPLY'" >&2
    exit 1
}

read -p "Enter a single item > "


#input is empty (invalid)
[ -z $REPLY ] && invalid_input

#input is multiple items
(( $(echo $REPLY | wc -w) > 1 )) && invalid_input

# is input a valid filename?
if [[ $REPLY=~ ^[-[:alnum:]\._]+$; then
    echo "'$REPLY is a valid filename."
    if [ -e $REPLY ]; then
        echo "And file '$REPLY' exists."
    else
        echo "However, file '$REPLY' does not exist."
    fi

    #is input a floating point number?
    if [[ $REPLY =~ ^-?[[:digit:]]*\.[[:digit:]]+$ ]]; then
        echo "'$REPLY' is a floating point number."
    else
        echo "'$REPLY' is not a floating point number."
    fi

    # is input an integer?
    if [[ $REPLY =~ ^-?[[:digit:]]+$ ]]; then
        echo "'$REPLY' is an integer."
    else
        echo "'$REPLY' is not an integer."
    fi
else
    echo "The string '$REPLY' is not a valid filename."
fi

我的问题始于尝试使用正则表达式搜索浮点数。

#!/bin/bash

# read-validate: valiate input

invalid_input()
{
    echo "Invalid input '$REPLY'" >&2
    exit 1
}

read -p "Enter a single item > "
valid_fname=$(egrep ^[-[:alnum:]\._]+$ <<< "$REPLY" | wc -m)
valid_float=$(egrep ^-?[[:digit:]]*\.[[:digit:]]+$ <<< "$REPLY" | wc -w)

#input is empty (invalid)
[ -z $REPLY ] && invalid_input

#input is multiple items
(( $(echo $REPLY | wc -w) > 1 )) && invalid_input

# is input a valid filename?
if [ "$valid_fname" -gt 0 ]; then
    echo "'$REPLY is a valid filename."
    if [ -e $REPLY ]; then
        echo "And file '$REPLY' exists."
    else
        echo "However, file '$REPLY' does not exist."
    fi

    #is input a floating point number?
    if [ "$valid_float" -gt 0 ]; then
    #if [[ $REPLY =~ ^-?[[:digit:]]*\.[[:digit:]]+$ ]]; then
        echo "'$REPLY' is a floating point number."
    else
        echo "'$REPLY' is not a floating point number."
    fi
else
    echo "The string '$REPLY' is not a valid filename."
fi

由于某些原因，即使正则表达式中包含\.，egrep也不会费心寻找小数点。这导致程序获取整数并将它们验证为浮点数。奇怪的是，单个数字不会被验证为浮点（0-9）。但是，两位数和以后的整数被验证为浮点数。我不知道为什么会这样。