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Module 24
cp

DESCRIPTION

The external cp command copies a file. It reads the contents of a file and creates a new file or overwrites an existing file. There are two basic formats of the cp command that allow you to:

*  Copy one file to another
*  Copy mutliple files to a directory
*  Copy input from your keyboard to a file
*  Copy a file to your terminal

COMMAND FORMAT

Following is the general format of the cp command.

     cp    [ -ip ]  source_file destination_file
     cp    [ -ipr ] source_file_list destination_directory
     cp -r [ -ip ]  source_directory destination_directory

Options

The following list describes the options that may be used to control how cp functions.

-i Interactive confirmation is required. You are prompted if the copy will overwrite an existing file. If your answer contains a y, the copy is performed. Otherwise, the copy is not performed.
-p Preserve the characteristics of the source_file. Copy the contents, modification times, and permission modes of the source_file to the destination files.
-r Recursively copy any source directories. If a directory is given as the source file, then all of its files and subdirectories are copied. The destination must be a directory.

Arguments

The following list describes the arguments that may be passed to the cp command.

source_file The existing file that will be copied
source_file_list The name of files and/or directories to be copied to a new destination directory
destination_file The name of the file the new copy will be named
destination_directory The name of the directory where a copy of the files will be made
source_directory The name of the directory from where copies are read

FURTHER DISCUSSION

The first format copies one ordinary file to a new file. The source_file is the pathname of the file being copied. The destination_file is the pathname of the file being copied to by cp.

The second format will copy one or more files to a specific directory. The source_file_list is a list of pathnames of the files being copied. If you specify a directory with the -r option, the entire directory tree is copied to the destination directory.

The third format allows you to copy an entire directory structure to a new directory.

If the destination_file exists and you have write permissions, cp will overwrite the contents of the file. The access permissions and ownership of the overwritten file will be used for the new destination_file.

If the destination_file does not exist, the access permissions of the source_file are used. Your ownership and group IDs are used for the new file if you are the user performing the cp command.

You cannot copy a file to itself.

Some common formats are:

   cp letter letter.bak    # make a backup copy of letter
   cp letter ../tmp        # copy letter to temporary working directory
   cp letter ../LTRS       # copy letter to original location (mv is better)
   cp /dev/tty note        # copy input from keyboard to file "note"

RELATED COMMANDS

Refer to the ln, mv, rm, chmod, chown, and ls commands described in modules 75, 91, 114, 17, 18, and 84.

APPLICATIONS

The cp command is used to make a copy of an existing file. It provides a way to create backup copies of files. If you accidently erase the current copy you are working on, you can fall back to the last backup copy you made.

You can copy a file to a temporary work area ($HOME/tmp is a good place) to perform changes. Then when you finish with the updates, copy the file back to its orginal location. You may want to write a shell script to perform these few tasks.

You may also want to use it to back up an entire work directory to a backup directory. Even though this uses up disk space, it may be well worth the cost. The trade off depends on the importance of the work you are performing versus the time it would take to recover or recreate the files if they are lost.

TYPICAL OPERATION

In this activity you use the cp command to copy a file. Begin at the shell prompt.

1.  List your HOME directory by typing ls and pressing Return. Notice the file named file1 in the following display.
      cj> ls
      bin      calendar  db   file1     letters   stuff
2.  Copy file1 to stuff by typing cp file1 stuff and pressing Return. This overwrites the contents already contained in the file named stuff.
3.  Type cp calendar letters and press Return to copy the calendar file to the letters directory.
4.  Turn to Module 114 to continue the learning sequence.


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