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
...
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,
including 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.
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.
The table below summarizes the commands, keyboard shortcuts, and special characters described in this section.
| Command/Shortcut | Description |
|---|---|
| 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 |
Introduction to the shell | Previous: Pipes and filters Next: Getting things from elsewhere