用 awk 替换 CSV 文件中的列值 [英] Replace column values in a CSV file with awk

问题描述

我有这个文件

错误日志

[00:00:00.284],501,

[00:00:00.284],501,

[00:00:00.417],5,5294100071980

[00:00:00.417],5,5294100071980

[00:00:02.463],501,

[00:00:02.463],501,

[00:00:05.169],501,

[00:00:05.169],501,

[00:00:05.529],501,

[00:00:05.529],501,

[00:00:05.730],501,

[00:00:05.730],501,

所以，如果字段 $3 为空，我想打印无价值"

so, if the field $3 its empty i want to print "No value"

我正在尝试这段代码

awk '{{FS=","} if($3=="") {print $1,$2,"No value"}}'

但它会打印出来

>[00:00:00.284] 501 No value
>[00:00:02.463] 501 No value
>[00:00:05.169] 501 No value
>[00:00:05.529] 501 No value
>[00:00:05.730] 501 No value
>[00:00:07.193] 501 No value
>[00:00:09.899] 501 No value
>[00:00:31.312] 501 No value

推荐答案

awk -F ',' -v OFS=',' '$1 { if ($3=="") $3="No value"; print}' in.txt

• 通过 -F 选项传递字段分隔符.
• 变量OFS，输出字段分隔符，设置为,，这样输出字段也用,分隔.李>
• 模式 $1 确保只处理非空行(即，仅当第一个字段非空时才执行关联的操作) - 如果您的输入文件没有空行，您可以删除此模式.
• 如果第三个字段为空，则分配字符串无值"
• 最后，输出行(带有可能修改的第三个字段).
• Passes the field separator via the -F option.
• Variable OFS, the output-field separator, is set to ,, so that output fields are also separated by ,.
• Pattern $1 ensures that only non-empty lines are processed (that is, the associated action is only executed if the first field is non-empty) - if your input file has no empty lines, you can remove this pattern.
• If the 3rd field is empty, it is assigned string "No value"
• Finally, the line (with the potentially modified 3rd field) is output.

以上是我建议您解决问题的方法，但以下是您原始命令的问题:

The above is how I suggest you approach the problem, but here are the problems with your original command:

• {{FS=","}...在您的单个操作中 - 由于没有为每个输入行执行前面的模式 - 您为每一行设置变量 FS - 这不仅是不必要的，而且 为时已晚，因为那时第一行已经被解析了(感谢@EdMorton)——或者将它设置在 BEGIN 块中(BEGIN { FS="," }) 或者，如我的回答，使用命令行选项 -F (-F ',').
• if($3=="") {...}
  只有当字段 $3 为空时，您才会产生输出 - 不过，可能您想输出 all 行，因此使用这种方法，您需要一个 else 分支(打印未修改的行).
• 打印 $1,$2,"No value"
, 字符.这是语法的一部分——它们只是将传递给 print 的参数分开.给定单独的参数，print 将它们与特殊的 OFS 变量的值连接起来，默认情况下其值为单个 space；要使用 , 代替，您必须将其分配给 OFS - 再次，在 BEGIN 块中或通过 -v 选项(-v OFS=',').
• {{FS=","}... Inside your single action - which due to not having a preceding pattern is executed for every input line - you set variable FS for every line - which is not only unnecessary but too late, because the first input line has already been parsed by that time (thanks, @EdMorton) - either set it in a BEGIN block (BEGIN { FS="," }) or, as in my answer, with command-line option -F (-F ',').
• if($3=="") {...}
  You only produce output if field $3 is empty - presumably, though, you want to output all lines, so with this approach you'd need an else branch (to print unmodified lines).
• print $1,$2,"No value"
  The , chars. here are part of the syntax - they simply separate the arguments passed to print. Given separate arguments, print concatenates them with the value of the special OFS variable, whose value is a single space by default; to use , instead, you have to assign it to OFS - again, either in a BEGIN block or via the -v option (-v OFS=',').

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