Question

我有以下代码：

function replaceappend() {
    awk -v old="$2" -v new="$3" '
        sub(old,new) { replaced=1 }
        { print }
        END { if (!replaced) print new }
    ' "$1" > /tmp/tmp$$ &&
    mv /tmp/tmp$$ "$1"
}

replaceappend "/etc/ssh/sshd_config" "Port" "Port 222"

它工作正常，但我希望修改它，以便awk命令只在行以该结果开头时才找到匹配项。因此，如果它正在寻找单词＆＃34; Port＆＃34;：

Port 123 # Test   <- It would match this one
This is a Port    <- It would not match this one

我试图查看其他帖子，询问＆＃34; Awk行以＆＃34;比如这个，但是我无法理解它：

awk, print lines which start with four digits

Answer 1

在正则表达式中，^仅匹配行的开头。因此，要仅在行的开头匹配Port，请写^Port。

例如，让我们创建一个文件;

$ cat >testfile
Port 123 # Test   <- It would match this one
This is a Port    <- It would not match this one

应用你的功能：

$ replaceappend testfile ^Port REPLACED

结果：

$ cat testfile 
REPLACED 123 # Test   <- It would match this one
This is a Port    <- It would not match this one

GNU documentation提供了有关GNU awk支持的正则表达式的更多信息。

仅当行以结果开始时，awk才匹配

1 个答案: