Add content to getting things section

lessons/shell/getting-things.md

@@ -2,6 +2,126 @@
 
 # Getting things from elsewhere
 
+While it's often srightforward to click to download items from a web browser,
+it's also possible to get them with shell commands,
+and the shell commands provide more flexibility.
+
+For example,
+the URL from which we downloaded the Software Carpentry sample data files is
+
+> https://swcarpentry.github.io/shell-novice/data/data-shell.zip
+
+Use the `curl` command to download this file programmatically:
+```
+$ curl https://swcarpentry.github.io/shell-novice/data/data-shell.zip -o data-shell-1.zip
+  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
+                                 Dload  Upload   Total   Spent    Left  Speed
+100  566k  100  566k    0     0  2037k      0 --:--:-- --:--:-- --:--:-- 2045k
+```
+Here, I used the `o` option to choose a slightly different name
+for the downloaded file,
+so as not to clobber the existing file.
+
+Verify that the file was downloaded:
+```
+$ ls -l *.zip
+-rw-r--r--  1 mpiper  staff  580102 Jul 30 16:22 data-shell-1.zip
+-rw-r--r--@ 1 mpiper  staff  580102 Jul 28 16:05 data-shell.zip
+```
+
+`curl` can do very cool things with wildcards, as well.
+Visit its (lengthy) man page to see all the options.
+
+The `wget` command provides functionality similar to `curl`,
+but with a slightly simpler call.
+```
+$ wget https://swcarpentry.github.io/shell-novice/data/data-shell.zip
+--2020-07-30 16:36:01--  https://swcarpentry.github.io/shell-novice/data/data-shell.zip
+Resolving swcarpentry.github.io... 185.199.109.153, 185.199.108.153, 185.199.111.153, ...
+Connecting to swcarpentry.github.io|185.199.109.153|:443... connected.
+HTTP request sent, awaiting response... 200 OK
+Length: 580102 (567K) [application/zip]
+Saving to: ‘data-shell.zip.1’
+
+data-shell.zip.1     100%[======================>] 566.51K  --.-KB/s    in 0.09s
+
+2020-07-30 16:36:01 (6.34 MB/s) - ‘data-shell.zip.1’ saved [580102/580102]
+```
+
+Verify that the file was downloaded:
+```
+$ ll *zip*
+-rw-r--r--  1 mpiper  staff  580102 Jul 30 16:22 data-shell-1.zip
+-rw-r--r--@ 1 mpiper  staff  580102 Jul 28 16:05 data-shell.zip
+-rw-r--r--@ 1 mpiper  staff  580102 Jul  1 01:44 data-shell.zip.1
+```
+
+
+## Unpacking files
+
+Because of their smaller size,
+it's more efficient to transfer a compressed file over the internet.
+
+The example files downloaded from Software Carpentry
+are compressed into a *zip archive*.
+We've already uncompressed these files into the **data-shell** directory
+through the operating system.
+Let's remove these files and instead uncompress the zip file using the shell.
+
+First, remove the existing **data-shell** directory:
+```
+$ rm -rf data-shell
+```
+Then use the `unzip` command to uncompress **data-shell.zip**:
+```
+$ unzip data-shell.zip
+Archive:  data-shell.zip
+   creating: data-shell/
+  inflating: data-shell/pizza.cfg
+  inflating: data-shell/.bash_profile
+   creating: data-shell/molecules/
+  inflating: data-shell/molecules/ethane.pdb
+  inflating: data-shell/molecules/cubane.pdb
+  ...
+```
+
+While zip files are common on Windows,
+*tar* files that use the more efficient gzip and bzip2 compressors
+are more common on Unix-based operating systems.
+
+Let's compress the **data-shell** directory
+with `tar` and compare file sizes:
+```
+$ tar -czf data-shell.tar.gz data-shell
+$ tar -cjf data-shell.tar.bz2 data-shell
+```
+In these commands,
+the `c` option creates an archive file,
+the `f` option provides the name of the archive file,
+and the `z` and `j` options specify gzip and bzip2 compression, respectively.
+The **.tar.gz** and **.tar.bz2** extensions are used by convention.
+
+Check sizes:
+```
+$ ls -lh data-shell.*
+-rw-r--r--  1 mpiper  staff   393K Jul 31 15:42 data-shell.tar.bz2
+-rw-r--r--  1 mpiper  staff   518K Jul 31 15:41 data-shell.tar.gz
+-rw-r--r--@ 1 mpiper  staff   567K Jul 28 16:05 data-shell.zip
+```
+Note that bzip2 < gzip < zip compression.
+In the directory listing, recall the `l` option provides a long listing.
+The `h` option provides "human readable" output.
+
+Uncompress these tarballs with:
+```
+tar -xf data-shell.tar.gz
+tar -xf data-shell.tar.bz2
+```
+Here, the `x` option is for uncompressing the archive file.
+In each case,
+the existing **data-shell** directory was clobbered
+when the archive was uncompressed.
+
 
 ## Summary
 
@@ -11,8 +131,6 @@ The table below summarizes the commands described in this section.
 | -------- | -----------
 | curl     | get files from an URL
 | wget     | get files from an URL (nonstandard)
-| rsync    | get files from remote machine
-| ssh      | login to remote machine
 | zip      | package and compress/uncompress files
 | gzip     | package and compress/uncompress files
 | tar      | package and compress/uncompress files