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

error.log

error.log

[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,

因此，如果字段$ 3为空，我想打印无值"

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"}}'

但可以打印

>[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,，因此输出字段也由,分隔.
• 模式$1确保仅处理非空行(即，仅当第一个字段为非空时才执行关联的动作)-如果输入文件中没有空行，则可以删除此模式.
• 如果第三个字段为空，则会为其分配字符串无值"
• 最后，输出该行(具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式，但是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=","}... 在您的单个操作内(由于没有前面的模式而对每条输入行都执行了)，您为每行设置了变量FS -这不仅不必要，而且为时已晚，因为第一条输入行已经被解析(感谢@EdMorton)-要么将其设置在BEGIN块(BEGIN { FS="," })中，要么按照我的回答，使用命令行选项(-F ',').
• if($3=="") {...}
  仅当字段$3为空时才产生输出-但是，大概想输出 all 行，因此使用这种方法，您需要一个else分支(以打印未修改的行).
• print $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，该变量的值默认为单个 space ；若要使用,，则必须再次在BEGIN块中或通过-v选项(-v OFS=',')将其分配给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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