如何使用sed在文本文件中查找对应位置并更新shell [英] How to use sed to find the corresponding place in a text file and update it shell

问题描述

Book name:author:price:Qty:Qty Sold
==================================
harry potter:james:12.99:197:101
===============================

我想更新 QTY，在这种情况下，它的值为 197，但我似乎无法用我的程序更新该值，请帮助我，因为我刚刚开始学习 shell 编程.谢谢

I want to update the QTY which is the value of 197 in this case but i cant seems to be able to update the value with my program please help me as i have just started learning shell programming. Thanks

function update_qty_available
{
grep -c "$title:$author" BookDB.txt > /dev/null # Look for a line with matching values

if [ $? == 0 ]; 
then # If found then offer to change Qty
echo "Update Qty to what?"
read newQty
sed -i "s/\($title:$author\):[^:]:[^:]*:/\1:$newQty/" BookDB.txt
    echo "Book's Qty has been updated successfully!"
fi

推荐答案

重构为使用 grep -q;修复 if 习惯用法；将搜索锚定到行首；使用 read -p 而不是单独的 echo；捕获括号内的价格，以免丢失；在正则表达式中添加缺少的重复；并在新数量值后添加分隔符冒号；此外，添加一个 else 子句，以便该函数不会静默失败.

Refactored to use grep -q; fix the if idiom; anchor the search to start of line; use read -p instead of a separate echo; capture the price inside the parens so that it's not lost; add the missing repeat in the regex; and add back the separator colon after the new qty value; also, add an else clause so that the function doesn't fail silently.

function update_qty_available
{
    if grep -q "^$title:$author:" BookDB.txt
    then
        read -p "Update Qty to what?" newQty
        sed -i "s/^\($title:$author:[^:]*\):[^:]*:/\1:$newQty:/" BookDB.txt
        echo "Book's Qty has been updated successfully!"
    else
        echo "$0: BookDB.Txt: no '$title' by '$author'" >&2
    fi
}

这篇关于如何使用sed在文本文件中查找对应位置并更新shell的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！