The Linux Command Line by William Shotts
This lesson will introduce you to the following commands:
- cp - copy files and directories
- mv - move or rename files and directories
- rm - remove files and directories
- mkdir - create directories
These four commands are among the most frequently used Linux commands. They are the basic commands for manipulating both files and directories.
Now, to be frank, some of the tasks performed by these commands are more easily done with a graphical file manager. With a file manager, you can drag and drop a file from one directory to another, cut and paste files, delete files, etc. So why use these old command line programs?
The answer is power and flexibility. While it is easy to perform simple file manipulations with a graphical file manager, complicated tasks can be easier with the command line programs. For example, how would you copy all the HTML files from one directory to another, but only copy files that did not exist in the destination directory or were newer than the versions in the destination directory? Pretty hard with with a file manager. Pretty easy with the command line:
[me@linuxbox me]$ cp -u *.html destination
Wildcards
Before I begin with our commands, I want to talk about a shell feature that makes these commands so powerful. Since the shell uses filenames so much, it provides special characters to help you rapidly specify groups of filenames. These special characters are called wildcards. Wildcards allow you to select filenames based on patterns of characters. The table below lists the wildcards and what they select:
| Wildcard | Meaning | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| * | Matches any characters | ||||||||||
| ? | Matches any single character | ||||||||||
| [characters] | Matches any character that is a member of the set characters. The set of characters may also be expressed as a POSIX character classsuch as one of the following:
| ||||||||||
| [!characters] | Matches any character that is not a member of the set characters |
Using wildcards, it is possible to construct very sophisticated selection criteria for filenames. Here are some examples of patterns and what they match:
| Pattern | Matches |
|---|---|
* | All filenames |
g* | All filenames that begin with the character "g" |
b*.txt | All filenames that begin with the character "b" and end with the characters ".txt" |
Data??? | Any filename that begins with the characters "Data" followed by exactly 3 more characters |
[abc]* | Any filename that begins with "a" or "b" or "c" followed by any other characters |
[[:upper:]]* | Any filename that begins with an uppercase letter. This is an example of a character class. |
BACKUP.[[:digit:]][[:digit:]] | Another example of character classes. This pattern matches any filename that begins with the characters "BACKUP." followed by exactly two numerals. |
*[![:lower:]] | Any filename that does not end with a lowercase letter. |
You can use wildcards with any command that accepts filename arguments.
cp
The cp program copies files and directories. In its simplest form, it copies a single file:
[me@linuxbox me]$ cp file1 file2
It can also be used to copy multiple files (and/or directories) to a different directory:
[me@linuxbox me]$ cp file... directory
A note on notation: ... signifies that an item can be repeated one or more times.
Other useful examples of cp and its options include:
| Command | Results |
|---|---|
cp file1 file2 | Copies the contents of file1 into file2. If file2 does not exist, it is created; otherwise, file2 is silently overwritten with the contents of file1. |
cp -i file1 file2 | Like above however, since the "-i" (interactive) option is specified, if file2 exists, the user is prompted before it is overwritten with the contents of file1. |
cp file1 dir1 | Copy the contents of file1 (into a file named file1) inside of directory dir1. |
cp -R dir1 dir2 | Copy the contents of the directory dir1. If directory dir2 does not exist, it is created. Otherwise, it creates a directory named dir1within directory dir2. |
mv
The mv command moves or renames files and directories depending on how it is used. It will either move one or more files to a different directory, or it will rename a file or directory. To rename a file, it is used like this:
[me@linuxbox me]$ mv filename1 filename2
To move files (and/or directories) to a different directory:
[me@linuxbox me]$ mv file... directory
Examples of mv and its options include:
| Command | Results |
|---|---|
mv file1 file2 | If file2 does not exist, then file1 is renamed file2. If file2 exists, its contents are silently replaced with the contents of file1. |
mv -i file1 file2 | Like above however, since the "-i" (interactive) option is specified, if file2 exists, the user is prompted before it is overwritten with the contents of file1. |
mv file1 file2 file3 dir1 | The files file1, file2, file3 are moved to directory dir1. If dir1 does not exist, mv will exit with an error. |
mv dir1 dir2 | If dir2 does not exist, then dir1 is renamed dir2. If dir2 exists, the directory dir1 is moved within directory dir2. |
rm
The rm command removes (deletes) files and directories.
[me@linuxbox me]$ rm file...
It can also be used to delete directories:
[me@linuxbox me]$ rm -r directory...
Examples of rm and its options include:
| Command | Results |
|---|---|
rm file1 file2 | Delete file1 and file2. |
rm -i file1 file2 | Like above however, since the "-i" (interactive) option is specified, the user is prompted before each file is deleted. |
rm -r dir1 dir2 | Directories dir1 and dir2 are deleted along with all of their contents. |
Be careful with rm!
Linux does not have an undelete command. Once you delete something with rm, it's gone. You can inflict terrific damage on your system with rm if you are not careful, particularly with wildcards.Before you use rm with wildcards, try this helpful trick: construct your command using ls instead. By doing this, you can see the effect of your wildcards before you delete files. After you have tested your command with ls, recall the command with the up-arrow key and then substitute rm for ls in the command.
mkdir
The mkdir command is used to create directories. To use it, you simply type:
[me@linuxbox me]$ mkdir directory...
Using Commands With Wildcards
Since the commands we have covered here accept multiple file and directories names as arguments, you can use wildcards to specify them. Here are a few examples:
| Command | Results |
|---|---|
cp *.txt text_files | Copy all files in the current working directory with names ending with the characters ".txt" to an existing directory named text_files. |
mv my_dir ../*.bak my_new_dir | Move the subdirectory my_dir and all the files ending in ".bak" in the current working directory's parent directory to an existing directory named my_new_dir. |
rm *~ | Delete all files in the current working directory that end with the character "~". Some applications create backup files using this naming scheme. Using this command will clean them out of a directory. |
