Exercise

Passing Data to a Script Exercise

Task

Build a second script from scratch, then feed it data three different ways: an argument, typed input, and a file.

Host: servera
Script: /home/student/scripts/shift_report.sh

Create a new script and make it executable

Same three steps as the last script: hashbang, content, chmod. You will do this in every scripting exercise from here on.
```
cd ~/scripts
vim shift_report.sh
```
```
#!/bin/bash
echo "Shift report filed"
```
```
chmod a+x shift_report.sh
./shift_report.sh
```
Take the technician name as an argument

$1 holds the first argument given on the command line.
```
vim shift_report.sh
```
```
echo "Shift report filed by $1"
```
Run it without an argument first. $1 is empty and the sentence reads badly, which is worth seeing once. Then run it with a name.
```
./shift_report.sh
./shift_report.sh "Jon Luc Picard"
```
Quote a name with spaces Without the quotes the shell splits it, and $1 holds only Jon.
Read the starship name from standard input

read takes a line from stdin and stores it in a variable.
```
vim shift_report.sh
```
```
echo "Which starship did you command?"
read -r system_name
echo "The $system_name"
```
Run it and type USS Enterprise when it asks.
```
cat shift_report.sh
./shift_report.sh "Jon Luc Picard"
```
Supply that input from a file

The script cannot tell the difference. It just reads a line from stdin, wherever stdin happens to come from.
```
echo "USS Enterprise" > worked_system.txt
cat worked_system.txt
./shift_report.sh "Jon Luc Picard" < worked_system.txt
```
Why this matters A script that reads stdin can be run by a person or fed by a file, with no change to the script.

Add a value produced by another command

$( ) runs the command inside it first, then substitutes its output.

vim shift_report.sh

log_file=$(basename /var/log/audit/audit.log)
echo "Recorded in $log_file"

./shift_report.sh "Jon Luc Picard" < worked_system.txt

Clean up

rm -f shift_report.sh worked_system.txt
cd ~