IT 244: Introduction to Linux/Unix

IT 244: Introduction to Linux/Unix
Class 16 Exercise

Copy 2 text files from ~tsoro/course_files/it244_files to your ex16 directory
```
    cp  ~tsoro/course_files/it244_files/foo[12].txt  .
```
Run ls to make sure the copy operation worked
```
    ls
```
Run cat on foo1.txt and foo2.txt
```
    cat  foo?.txt
```
When you give cat two files as arguments, it prints the first, followed by the second.
Run cat on a file that does not exist
```
    cat  xxx.txt
```
cat sends an error message to standard error, which is the terminal by default.
Run cat on two files, one nonexistent, sending standard output to a file
```
    cat  foo1.txt xxx.txt  >  foo_xxx.txt
```
The error message went to the terminal, not the file.
Print the contents of foo_xxx.txt
```
    cat  foo_xxx.txt
```
Notice that the error message was not inserted into the file.
Run cat on two files, one nonexistent, sending standard error to a file
```
    cat  foo1.txt xxx.txt  2>  errors.txt
```
Notice that the contents of the first file is displayed on the terminal, but not the error message.
Print errors.txt
```
    cat  errors.txt
```
errors.txt contains the error message that would have gone to the screen if you had not redirected standard error.
Run cat on two files, one nonexistent, sending all output to a file
```
    cat  foo1.txt  xxx.txt  &>  everything.txt
```
Noting appears on the screen.
Print everything.txt
```
    cat  everything.txt
```
Both the output and error message were redirected to the same file

Create a script to keep track of the contents of your current directory
```
    nano  dir_snap.sh
```
Enter the hashbang line
```
    #!/bin/bash
```

Enter a comment describing what the script does

    #
    # This script takes periodic snapshots of the current directory and
    # sends them to a file "snapshot.log"

Enter a blank line

This makes the script more readable.
Enter a line which will record the date
```
    date  >>  snapshot.log
```
To be useful, the log file needs a date stamp.

Notice that we are appending to a file, even though it doesn't exist at first.

If you use the append symbol >> on a file that doesn't exist, that file will be created and the output sent to it.
Enter a line which will record the current directory
```
    pwd  >> snapshot.log
```

Enter a separator line

    echo  ------------------------  >>  snapshot.log

This makes the file more readable.

Enter a line to send a long listing for all files to the log file
```
    ls  -l  >>  snapshot.log
```
Enter a line to send a blank line to the log file
```
    echo  >>  snapshot.log
```
This will make the log more readable.

Enter a line to show the script is finished

    echo sent directory listing to snapshot.log

Save the file and exit nano
Make the file executable
```
    chmod  755  dir_snap.sh
```
Look at the permissions on the script
```
    ls  -l  dir_snap.sh
```
Run the script
```
    ./dir_snap.sh
```
Look at the contents of snapshot.log
```
    cat  snapshot.log
```
Run the script again
```
    ./dir_snap.sh
```
Notice that additional information is added to the end of the file.
Look at the contents of snapshot.log
```
    cat  snapshot.log
```
Testing
You will not be able to run my test script for this exercise.
Instead, run the script in your ex16 and then run cat on snapshot.log.
Let me check your script