在 awk 命令 shell 中使用日期

Question

I have a question related to awk command in shell. We have a input csv file with following values:

Control_Time;Report_Name
2020-08-10;Report A
2020-06-10;Report B
2020-07-01;Report C

My goal is to check all the rows in this file and filter (copy) only the rows which have a date greater than first day of previous month. So, I created an variable called previous_month which is following:

previous_month=$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)

This variable works fine, but I am not able to work with it in awk statement which I want to use for filtering data into the output file.

I tried following statement just for printing the previous_month and it is not working.

awk -v previous_month="$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)" '{print previous_month}'

However, echo previous_month works fine and it gives me the value 2020-07-01. Is there any way how to work with this custom variable? Thank you for all advices!

Answer 1

You were close, could you please try following.

awk -v pre_date=$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d) '
BEGIN{
  FS=OFS=";"
}
$1==pre_date
'  Input_file

Improvements in OP's code attempts:

• We could create an awk variable where we could mention date shell command itself, so taken OP's command of date and placed it inside pre_date awk variable.
• Since OP wants to match previous month's date with Input_file so first we need to set delimiter as ; as per OP's sample Input_file.
• Then we need to compare $1 1st field of Input_file with awk variable and check condition if both are same then no action mentioned so by default print of current line will happen.

Answer 2

Your command works just fine. awk is just working on lines either given by stdin or by a file. Or what you're typing.

Try the following:

echo "hello world" | awk -v previous_month="$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)" '{print previous_month}'

This will print the date once, since you provided one line via stdin.

Or

awk -v previous_month="$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)" '{print previous_month}' filename

This will print the date for each line in the file.

Or

awk -v previous_month="$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)" '{print previous_month}'

(and now type something and press enter)

This will print the date as well each time you press enter.

Answer 3

thank you both for your answers. It was really helpful, I did not realized. that I need to use the input file, So, it worked fine. but I had to add input file.

Final query is following:

awk -v previous_month="$(date -d "`date +%Y%m01` -1 month" +%Y-%m-%d)" '{if ($1 > previous_month) print $0}' inputFile > outputFile;

It could help to someone else.