CODEWITHSUNDEEP
bashshell
Hua Cha
Hua Cha

Reputation: 117

How to traverse through a file and apply date in bash?

I'm sure this has been answered but having trouble with my google search.

File is like this:

2020-01-01 10:33
2020-01-01 14:04
2020-01-01 17:22
2020-01-20 14:04
2020-01-21 03:33
2020-01-22 14:06

How do I traverse through each line and apply date +"%b%d" so that the file looks like:

Jan1 10:33
Jan1 14:04
Jan1 17:22
Jan20 14:04
Jan21 03:33
Jan22 14:06

Upvotes: 1

Views: 70

Answers (1)

David C. Rankin
David C. Rankin

Reputation: 84579

You have basically two options.

  1. using shell, loop over each line in your file, reading each line into a variable and output with date using the format +'%b%d %H:%M'; or
  2. using GNU awk, create a datespec from each line, and pass to mktime to create a timestamp which can then be used with strftime to output the format "%b%d %H:%M".

Bash Solution

while read -r line; do 
    date -d "$line" +'%b%d %H:%M'
done < file

GNU awk Solution

awk '{
    gsub(/[-:]/," ",$0)                # remove '-' and ':'
    ts=mktime($0 " 00")                # add " 00" creating datespec, create timestamp
    print strftime("%b%d %H:%M",ts)    # output new date format
}' file

(note: mawk, at least from version 1.3.3 on also supports mktime and strftime)

Example Output

In both cases the output is the same:

Jan01 10:33
Jan01 14:04
Jan01 17:22
Jan20 14:04
Jan21 03:33
Jan22 14:06

Look things over and let me know if you have additional questions.

Upvotes: 3

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