Shell Commands

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1. Dates

First run the date command in the terminal.
```
$ date
```
Output: will be something like this...
```
Mon 27 Feb 13:58:41 GMT 2023
```
So how do we get different formats?

Well if in doubt you can check the man pages or use the commands --help flag
```
$ date --help
```
Looking at the output workout how to produce this format:
```
> 20230227
```
Answer
```
date +"%Y%m%d"
```

Now modify this output to display:

> Year: 2023, Month: 02, Day: 27

Answer

date +"Year: %Y, Month: %m, Day: %d"

The most common formatting characters:
- %D – Display date as mm/dd/yy
- %Y – Year (e.g., 2020)
- %m – Month (01-12)
- %B – Long month name (e.g., November)
- %b – Short month name (e.g., Nov)
- %d – Day of month (e.g., 01)
- %j – Day of year (001-366)
- %u – Day of week (1-7)
- %A – Full weekday name (e.g., Friday)
- %a – Short weekday name (e.g., Fri)
- %H – Hour (00-23)
- %I – Hour (01-12)
- %M – Minute (00-59)
- %S – Second (00-60)
Using the above information and what previous steps reproduce the ISO 8601 standard for datetime.
```
> 2023-02-27T12:08:45Z
```
Answer
```
$ date +"%Y-%m-%dT%H:%M:%S:%NZ"
```
- %Y – Year (e.g., 2020)
- %m – Month (01-12)
- %d – Day of month (e.g., 01)
- T – self delimeter
- %H – Hour (00-23)
- : – self delimeter
- %M – Minute (00-59)
- : – self delimeter
- %S – Second (00-60)
- Z – self delimeter
Amend the last command so that after seconds you get nano seconds.
```
> 2023-02-27T12:14:03:281999558Z
```
Answer
```
$ date +"%Y-%m-%dT%H:%M:%S:%NZ"
```
- %Y – Year (e.g., 2020)
- %m – Month (01-12)
- %d – Day of month (e.g., 01)
- T – self delimeter
- %H – Hour (00-23)
- : – self delimeter
- %M – Minute (00-59)
- : – self delimeter
- %S – Second (00-60)
- : – self delimeter
- %N – nanoseconds (000000000..999999999)
- Z – self delimeter

Task 2. Manipulating inputs and outputs

working with the previous command lets strip out the T,:s and Z so that we are left with only numnbers.
Using awk we can manipulate the output by piping | the output of date into awk - first run this command
```
$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk "{print $1}" 
> 2023-02-27T12:20:40:005619503Z   
```
- awk with the argument print $1 will print the first argument... ie the output of date

Now lets remove the T

$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F 'T' '{print $1}'
> 2023-02-27

What happens when you do $2 on the same command as above?
Answer
```
> 12:50:48:341942600Z
```
This is because the input has been split and now
- $1 = 2023-02-27
- $2 = 12:20:40:005619503Z

Change the delimeter -F 'T' to -F ':' and repeat both steps as before:

Answer

$  date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F ':' '{print $1}'
>  2023-02-27T12

$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F ':' '{print $2}'
  55
$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F ':' '{print $3}'
  32
$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F ':' '{print $4}'
  473072761Z

You can put these together using the print {$2$3$4$}, try. sh date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F ':' '{print $2$3$4}' 5719707652042Z

Experiment with this and consider piping with awk to see if you can get:

20230227130026355420256

Answer

$ date +"%Y-%m-%dT%H:%M:%S:%NZ" | awk -F '[-T:Z]' '{print $1$2$3$4$5$6$7$8$9}'
20230227130026355420256

NOS Exercises

Shell Commands

JupyterHub

1. Dates

Task 2. Manipulating inputs and outputs