如何在重定向文件時獲取提示信息？

Question

我有一個文件的測試是在目錄中已經存在，當我使用

`cat > test` or `ls > test` 

文件中的內容將被截斷，且數據會丟失，所以我重定向文件之前，想提示信息。你的幫助將是最有用的。

在此先感謝。

Answer 1

一個例子可能是這樣的：

#!/bin/sh 

# Prevent > from overwriting files, use >| to overwrite files anyway 
# It's good for safety to always enable this... 
set -C 

file=xxx 

# Test if file exist with -f 
if [ -f "$file" ]; then 
    echo "Overwrite $file? [Y/n]" 

    # Read user input 
    read answer 

    # Is the answer "n" or "N", we exit 
    # The default is to continue on any other input (you could change this, of course) 
    case "$answer" in 
     [nN]) exit 2 ;; 
    esac 
fi 

# Overwrite the file, we use >| because we set noclobber 
echo 'New' >| "$file"