将值传递给 xargs 中的多个命令

Question

我正在尝试在 xargs 中执行多个命令。我在这里看到的问题是管道值“%”仅传递给 xargs 中的第一个子命令，而不传递给第二个子命令。通过交换命令位置验证相同，但第二个命令始终无法获得 '%'

所需的值

Command-1

aws ec2 describe-instances --query 'Reservations[].Instances[?(LaunchTime>=`2015-01-01` && LaunchTime<=`2015-02-28`)][].{id: InstanceId, launched: LaunchTime}' | jq --raw-output '.[] | .id' | xargs -n 1 -I % sh -c 'aws cloudwatch get-metric-statistics --metric-name NetworkPacketsIn --start-time 2018-01-01T00:00:00Z --end-time 2018-02-28T23:59:59Z --period 2592000 --namespace AWS/EC2 --statistics Maximum --dimensions Name=InstanceId,Value=%; echo instance: %;'

输出：

{
    "Label": "NetworkPacketsIn",
    "Datapoints": []
}
instance: %
{
    "Label": "NetworkPacketsIn",
    "Datapoints": []
}
instance: %

Command-2

aws ec2 describe-instances --query 'Reservations[].Instances[?(LaunchTime>=`2015-01-01` && LaunchTime<=`2015-02-28`)][].{id: InstanceId, launched: LaunchTime}' | jq --raw-output '.[] | .id' | xargs -n 1 -I % sh -c 'echo instance: %; aws cloudwatch get-metric-statistics --metric-name NetworkPacketsIn --start-time 2018-01-01T00:00:00Z --end-time 2018-02-28T23:59:59Z --period 86400 --namespace AWS/EC2 --statistics Maximum --dimensions Name=InstanceId,Value=%;'

输出

instance: i-3e4fab33
{
    "Label": "NetworkPacketsIn",
    "Datapoints": []
}
instance: i-c2abbac8
{
    "Label": "NetworkPacketsIn",
    "Datapoints": []
}

Answer 1

TL;DR Mac xargs 参数在替换完成后不能超过 255 个字节。

缩短您的论点并在最后一条命令中保留分号修复了错误：

aws ec2 describe-instances --query 'Reservations[].Instances[?(LaunchTime>=`2015-01-01` && LaunchTime<=`2015-02-28`)][].{id: InstanceId, launched: LaunchTime}' | jq --raw-output '.[] | .id' | xargs -I % sh -c 'aws cloudwatch get-metric-statistics --metric-name NetworkPacketsIn --start-time 2018-01-01T00:00:00Z --end-time 2018-02-28T23:59:59Z --period 86400 --namespace AWS/EC2 --statistics Maximum --dimensions Name=InstanceId,Value=%;echo id=%'

这是更长的答案以及一些证明它的测试。

来自xargs man page：

 -I replstr
         Execute utility for each input line, replacing one or more occurrences of replstr in up to replacements (or
         5 if no -R flag is specified) arguments to utility with the entire line of input.  The resulting arguments,
         after replacement is done, will not be allowed to grow beyond 255 bytes; this is implemented by concatenat-
         ing as much of the argument containing replstr as possible, to the constructed arguments to utility, up to
         255 bytes.  The 255 byte limit does not apply to arguments to utility which do not contain replstr, and fur-
         thermore, no replacement will be done on utility itself.  Implies -x.

OP 传递给 xargs

的参数

'aws cloudwatch get-metric-statistics --metric-name NetworkPacketsIn --start-time 2018-01-01T00:00:00Z --end-time 2018-02-28T23:59:59Z --period 2592000 --namespace AWS/EC2 --statistics Maximum --dimensions Name=InstanceId,Value=%; echo instance: %;'

是250字节。当 % 被 AMI ID 替换时，它会超过 255 字节的限制并爆炸。

如果您想自己测试一下，请尝试以下操作，参数有 254 个字节：

echo blah |xargs -I % sh -c 'export blah=%; echo $blah; echo $blah; echo $blah;\
echo $blah; echo $blah; echo $blah;echo $blah; echo $blah; echo $blah;echo $blah;\
echo $blah; echo $blah;echo $blah; echo $blah; echo $blah;echo $blah; echo $blah;\
echo $blah;echo $blah;echo $blah;'

这会将单词 blah 正确地传递给每个 echo 语句。

blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah

在末尾再添加一个 echo $blah;，使字节总数达到 265 字节，它爆炸了：

% % % % % % % % % % % % % % % % % % % %

为了使 long post 更长，我将 instance id 传递给带有 --instance-ids 开关的 describe-instances 命令并且它按预期工作，因为参数扩展低于 255 个限制。

aws ec2 describe-instances --query 'Reservations[].Instances[?(LaunchTime>=`2015-01-01` && LaunchTime<=`2015-02-28`)][].{id: InstanceId, launched: LaunchTime}' | jq --raw-output '.[] | .id' | xargs  -I % sh -c 'echo instance: %; aws ec2 describe-instances --instance-ids=%; '

将值传递给 xargs 中的多个命令

Passing value passing to multiple commands in xargs

xargs

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