在文件 sip.conf 或任何基於文本的文件中的字元串“nat = no”之前添加一行“allow = alaw”

在文件 sip.conf 或任何基於文本的文件中，在字元串“nat = no”之前添加一行“allow = alaw”。如果在“nat = no”之前已經存在“allow = alaw”，則不應添加。

文件內容：

secret =
nat = no
progressinband = yes

allow = ulaw
allow = alaw
nat = no
progressinband = yes

disallow = all
allow = ulaw
nat = no
progressinband = yes

我的嘗試：

awk '/nat = no/ { if(lastLine == "allow = alaw") { print } } { lastLine = $0 }' sip.conf

awk -v add="allow = alaw" '/^nat = no$/&&lastLine!=add{print add}{lastLine=$0}1' sip.conf

• -v add="allow = alaw"將變數設置add為 awk。

• /^nat = no$/&&lastLine!=add檢查目前行是否完全是“nat = no”，如果最後一行不是我們要添加的行，“allow = alaw”。如果真實，

  • {print add}列印要添加的行。

• {lastLine=$0}保存目前行值，僅在下一個循環中使用。

• 1列印目前行。

在一個最小的例子中sip.conf：

secret =
nat = no
progressinband = yes

allow = ulaw
allow = alaw
nat = no
progressinband = yes

disallow = all
allow = ulaw
nat = no
progressinband = yes

$ awk -v add="allow = alaw" '/^nat = no$/&&lastLine!=add{print add}{lastLine=$0}1' sip.conf > out
$ mv out sip.conf
$ cat sip.conf
secret =
allow = alaw
nat = no
progressinband = yes

allow = ulaw
allow = alaw
nat = no
progressinband = yes

disallow = all
allow = ulaw
allow = alaw
nat = no
progressinband = yes

引用自：https://unix.stackexchange.com/questions/600274