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Manoj Kumar
Asked: 2019-07-17 00:50:39 +0800 CST

How to remove the first colon ':' from a timestamp?

  • 772

I am new to programming!!

Can anyone help to remove the : at the first position in a timestamp: :29.06.2019 23:03:17

Presently I am trying to do it using awk/cut commands as shown below:

TDS="$(grep 'Logfile started' process.log |  awk '{print $3,$4}' | cut -d: -f2)"
echo "$TDS"


29.06.2019 23

And the output is not what I wanted! I want to print it as 29.06.2019 23:03:17.

command-line bash awk cut-command

6 Answers

  1. Best Answer

    To cut off the first character, you can also use cut -c:

    $ echo ":29.06.2019 23:03:17" | cut -c 2-
29.06.2019 23:03:17
    • 14

  2. Use

    cut -d: -f2-

    instead of 

    cut -d: -f2

    to get anything from the second field to the end of line:

    TDS="$(grep 'Logfile started' process.log |  awk '{print $3,$4}' | cut -d: -f2-)"
echo "$TDS"
    • 11

  3. Here is a sed solution:

    $ echo ':29.06.2019 23:03:17' | sed 's/^://'
29.06.2019 23:03:17

    What the command sed 's/^://' is doing is substitute s the colon character : from the beginning ^ of each line with the empty string //.

    Here is a tricky awk solution, where we changing the field separator to ^:, described above, and output the second field (of each line):

    $ echo ':29.06.2019 23:03:17' | awk -F'^:' '{print $2}'
29.06.2019 23:03:17

    The task could be accomplished also with grep (explanation), probably this could be the fastest solution for large amount of data:

    $ echo 'Logfile started :29.06.2019 23:03:17' | grep -Po '^Logfile started :\K.*'
29.06.2019 23:03:17

    Or process the file directly by the following command, where the limitation ^ is removed:

    grep -Po 'Logfile started :\K.*' process.log

    The above could be achieved also by sed and capture groups ()->\1:

    sed -nr 's/^.*Logfile started :(.*)$/\1/p' process.log

    Where the expression ^.*<something>.*$ will match the whole line, that contains <something>. The command s/old/new/ will substitute this line by the content of the first capture group (the expression in the brackets could be more concrete). The option -r enables the extended regular expressions. The option -n will suppress the normal output of sed and finally the command p will print the matches.

    • 8

  4. awk is a cool tool, and you can solve very complex tasks with it. But for your question I would rather stick to the basic capabilities of bash.

    For this easy substing removal, I would do the following:

    zehe="Logfile started :29.06.2019 23:03:17"
echo "${zehe#*:}"

    this will print:

    29.06.2019 23:03:17

    When I was in your position and started to learn programming and bash, I learned a lot of this Handbook:

    ABS - Advanced Bash-Scripting Guide

    Some more examples and interesting information to your problem can be found here, look for 'Substring Removal'.

    • 8

  5. Since you're already processing this in awk, you may as well do the whole thing directly:

    $ echo "foo bar :29.06.2019 23:03:17" |  awk '{sub(/^:/,"",$3); print $3,$4}' 
29.06.2019 23:03:17

    The sub command's general format is sub(/REGEX/, REPLACEMENT, TARGET) and will replace all matches for the regular expression REGEX with the string REPLACEMENT in the input string TARGET. Here, we are replacing the first : (^ means "the beginning") from the 3rd field ($3) with nothing.

    Of course, if you're doing that in awk, you may as well do everything in awk and get the whole thing done in a single operation:

    $ echo "Logfile started :29.06.2019 23:03:17" | 
    awk '/Logfile started/{sub(/^:/,"",$3); print $3,$4}' 
29.06.2019 23:03:17

    Or, in your case:

    TDS="$(awk '/Logfile started/{sub(/^:/,"",$3); print $3,$4}' process.log)"
echo "$TDS"
    • 6

  6. Another bash solution:

    $ echo "Logfile started :29.06.2019 23:03:17" | xargs bash -c 'echo "${2#*:} $3"'
29.06.2019 23:03:17
    • This uses the pipeline instead of intermediate variable assignment.
    • The command xargs converts stdin (standard input) to positional parameters for bash command.
    • Replace echo with tail -n1 /path/to/reportfile.txt.
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