Add content for finding things section

lessons/shell/finding-things.md

@@ -2,6 +2,121 @@
 
 # Finding things
 
+The `grep` command is a powerful tool for matching patterns in files.
+Let's use it to look for unicorns in our files:
+```
+$ grep -r unicorn .
+./data-shell/creatures/unicorn.dat:1:COMMON NAME: unicorn
+Binary file ./data-shell.zip matches
+```
+The `r` option performs a recursive search,
+starting at the current directory,
+specified by the dot `.`.
+Note that `grep` searched both text and binary files for the matching pattern.
+To omit binary files from the search,
+use the `I` option:
+```
+$ grep -rI unicorn .
+./data-shell/creatures/unicorn.dat:1:COMMON NAME: unicorn
+```
+
+To search only within the current directory,
+the syntax of `grep` is slightly different.
+Let's find all instances of the word "octane" in the files
+in the current directory:
+```
+$ grep octane *
+grep: data-shell: Is a directory
+Binary file data-shell.zip matches
+molecule_pdb_lengths:4:  30 octane.txt
+molecule_pdb_lengths.bak:4:  30 octane.pdb
+```
+Note that I used the wildcard to denote all files in the current directory.
+
+The `find` command recursively locates all files that match a search pattern.
+Let's find all the files with the extension **.txt**:
+```
+$ find . -iname "*.txt"
+./data-shell/data/amino-acids.txt
+./data-shell/data/animal-counts/animals.txt
+./data-shell/data/animals.txt
+./data-shell/data/morse.txt
+./data-shell/data/planets.txt
+...
+```
+The search started at the current directory, `.`
+The `iname` option directs `find` to ignore case in the search.
+
+In another example,
+let's use `find` to recursively locate all the directories
+under the current directory:
+```
+$ find . -type d
+.
+./data-shell
+./data-shell/creatures
+./data-shell/data
+./data-shell/data/animal-counts
+...
+```
+
+## Command documentation
+
+In the examples above (and in previous sections),
+options for commands are frequently demonstrated.
+To view a full list of options for any command,
+use the `man` command to pull up its manual page.
+For example, to get information about `find`, type:
+```
+$ man find
+```
+The `man` command displays documentation for `find`,
+incuding all options and several examples,
+in a pager.
+The man page for `find` is quite long.
+Press `q` in the pager to quit and return to the terminal.
+
+
+## Command history
+
+Every command you enter is logged.
+To see the record of commands,
+use `history`:
+```
+$ history
+```
+The entire command history is dumped to the terminal.
+To view only the last five commands (for example),
+pipe the output of `history` through `tail`:
+```
+$ history | tail -5
+  631  find . -type d
+  632  man find
+  633  man man
+  634  man find
+  635  history
+```
+
+How many times have you referenced `find`?
+```
+$ history | grep find | wc -l
+      32
+```
+
+The exclamation point, or bang, `!` can be used to match a command in history.
+For example, to execute the last call to `man`, type:
+```
+$ !man
+man find
+```
+
+To search history beyond the last instance of a command,
+use the `Ctrl-r` keybinding.
+At the prompt,
+type `Ctrl-r`, then a search term.
+Keep hitting `Ctrl-r` to move back through history.
+
+
 
 ## Summary
 
@@ -12,14 +127,10 @@ and special characters described in this section.
 | ---------------- | -----------
 | grep             | match text in files
 | find             | match filenames
+| man              | show documentation for command
 | history          | record of commands
+| !                | repeat command matched from history
 | Ctrl-r           | reverse search through history
-| !                | repeat command from history
-| man              | show documentation for command
-| env              | show environment variables
-| echo             | print variables to terminal
-| which            | show location of command
-| alias            | make a shortcut for a command
 
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