one case（GNU sed）

sed -E '
/^\s*-\s*image:\s*ngnix/{
  :top
  N
  /imagePullPolicy/!btop
  s/(imagePullPolicy:).*/\1 \{\}/
}' file.yaml

然而，这可能不是通用的。

使用任何POSIX awk：

$ cat tst.sh
#!/usr/bin/env bash

awk '
    match($0,/^[[:space:]-]*/) {
        if      ( RLENGTH > prevRlength ) { indent++ }
        else if ( RLENGTH < prevRlength ) { indent-- }
        prevRlength = RLENGTH

        key = val = substr($0,RLENGTH+1)
        sub(/[[:space:]]*:.*/,"",key)
        sub(/[^:]*:[[:space:]]*/,"",val)

        indent2key[indent] = key
    }

    (indent == 2) && (indent2key[0] == "spec") && (indent2key[1] == "containers") {
        if ( $1 == "-" ) {
            gotImage = 0
        }

        if ( (key == "image") && (val ~ /^ngnix:/) ) {
            gotImage = 1
        }

        if ( gotImage && (key == "imagePullPolicy") && (val == "IfNotPresent") ) {
            sub(/:.*/,": {}")
        }
    }

    { print }
' "${@:--}"

$ ./tst.sh file
kind: Pod
metadata:
  name: abc12
spec:
  containers:
  - image: ubuntu:latest
    name: Ubuntu
    imagePullPolicy: IfNotPresent
  - image: ngnix: latest
    name: Nginx
    imagePullPolicy: {}

上面假设image:总是在imagePullPolicy:之前，就像你发布的例子一样。

使用GNU sed

$ sed -E ':a;/- image: ngnix: latest/,/- image:/{n;s/(imagePullPolicy: ).*/\1{}/;ba}' input_file
kind: Pod
metadata:
  name: abc12
spec:
  containers:
  - image: ubuntu:latest
    name: Ubuntu
    imagePullPolicy: IfNotPresent
  - image: ngnix: latest
    name: Nginx
    imagePullPolicy: {}
...

首先，修复YAML第9行：image: ngnix: latest =〉image: nginx:latest（2个错误）。

固定输入：

kind: Pod
metadata:
  name: abc12
spec:
  containers:
    - image: ubuntu:latest
      name: Ubuntu
      imagePullPolicy: IfNotPresent
    - image: nginx:latest
      name: Nginx
      imagePullPolicy: IfNotPresent

使用正确的YAML解析器，yq：

yq -y '
  (
    .spec.containers[] | 
     select(.image=="nginx:latest" and .imagePullPolicy=="IfNotPresent")
    .imagePullPolicy
   ) = {}
' file

来自jq@libera.irc的emanuele6

Online Demo

输出

kind: Pod
metadata:
  name: abc12
spec:
  containers:
    - image: ubuntu:latest
      name: Ubuntu
      imagePullPolicy: IfNotPresent
    - image: nginx:latest
      name: Nginx
      imagePullPolicy: {}

编辑inplace，可以使用-yi。

非常简单的sed，假设唯一的IfNotPresent字符串是你想要替换的image: ngnix到imagePullPolicy的行：

sed '/image: ngnix:/,/imagePullPolicy/ s/IfNotPresent/{}/' file.yaml

换句话说，找到特定的行范围，然后在该/START/,/END/范围内进行最简单的替换