3    Managing Files

This chapter describes how to manage files on your system. After completing this chapter, you will be able to:

• List files

• Display and print files

• Link files

• Copy, rename, and move files

• Compare and sort files

• Remove files from the system

• Determine file type

To learn about managing files, follow the examples in this chapter. Do each example in order so that the information on your screen is consistent with the information in this book.

Before you can work through the examples, you must be logged in and your login directory must contain the following three files created in Chapter 2: file1, file2, and file3. To produce a listing of the files in your login directory, enter the ls command, which is explained in the following section. If you are using files with different names, make the appropriate substitutions as you work through the examples.

In the following examples, when you are asked to return to your login directory, enter the cd (change directory) command as follows:

$  cd

$

In the preceding example, the dollar sign ($) represents the shell prompt. Your shell prompt may vary.

In addition, before working on the examples in this chapter, create a subdirectory called project in your login directory. To do so, enter the following mkdir (make directory) command from your login directory:

$  mkdir project

$

For more information on the cd and mkdir commands, see Section 4.2 and Section 4.1 respectively.

3.1    Listing Files (ls)

You can display a listing of the contents of one or more directories with the ls (list directory) command. This command produces a list of the files and subdirectories (if any) in your current directory. You can also display other types of information, such as the contents of directories other than your current directory.

The format of the ls command is:

ls

The ls command has a number of options, called flags that enable you to display different types of information about the contents of a directory. Refer to Section 3.1.3 for information about these flags.

3.1.1    Listing Contents of the Current Directory

To list the contents of your current directory, enter:

$  ls

Used without flags in this format, the ls command lists the names of the files and directories in your current directory:

$  ls

file1     file2     file3     project
$

You may also list portions of your current directory's contents by using the command format:

ls filename

The filename entry can be the name of the file or a list of filenames separated by spaces. You may also use pattern-matching characters to specify files. See Chapter 2 for information on pattern matching.

For example, to list the files whose names begin with the characters file, you would enter the following command:

$  ls file*

file1  file2  file3
$

3.1.2    Listing Contents of Other Directories

To display a listing of the contents of a directory other than your current directory, use the following format:

ls dirname

The dirname entry is the pathname of the directory whose contents you want to display.

In the following example, the current directory is your login directory, and you want to display the /users directory. Your system may contain another directory with a name similar to the /users directory. The name of the /users directory is preceded by a slash (/), which indicates that the system should begin searching from the root directory.

$  ls /users

amy     beth    chang   george  jerry   larry
mark    monique ron
$

The ls command lists directory and filenames in collated order as determined by the current locale. For more information about locales (as used with internationalization), see Appendix C.

3.1.3    Flags Used with the ls Command

In its simplest form, the ls command displays only the names of files and directories contained in the specified directory. However, ls has several flags that provide additional information about the listed items or change the way in which the system displays the listing.

When you want to include flags with the ls command, use the following format:

ls -flagname(s)

The -flagname(s) entry specifies one or more flags (options) that you are using with the command. For example, the -l flag produces a long listing of the directory contents. Note also that all ls flags are preceded by the dash character (-).

If you want to use multiple flags with the command, enter the flag names together in one string:

$  ls -lta

Table 3-1 lists some of the most useful ls command flags.

Table 3-1: The ls Command Options

The following example shows a long (-l) listing of a current directory. The name larry shows the owner of the files. Your username and group name will replace larry and system on the screen.

$  ls -l

total 4
-rw-r--r--  1 larry   system   101 Jun  5 10:03 file1
-rw-r--r--  1 larry   system    75 Jun  5 10:03 file2
-rw-r--r--  1 larry   system    65 Jun  5 10:06 file3
drwxr-xr-x  2 larry   system    32 Jun  5 10:07 project
$

Table 3-2 explains the information displayed on your screen after you enter the ls -l command.

Table 3-2: The ls -l Command Information

Table notes:

1. For more information on permissions, see Chapter 5.

2. For an explanation of file links, see Section 3.4.

There are other ls command flags that you may find useful as you gain experience with the operating system. For detailed information about the ls command flags, see the ls(1) reference page.

3.2    Displaying Files

You can view any text file stored on your system with a text editor. However, if you want to just look at a file without making any changes, you may view it (with or without screen formatting) using a variety of operating system commands. The following sections describe these commands.

3.2.1    Displaying Files Without Formatting (pg, more, cat)

The following commands display a file just as it is, without adding any special characteristics that govern the appearance of the contents:

• pg

• cat

• more

For information on displaying files with formatting, see Section 3.2.2.

To display a file without formatting, the general format is:

command filename

The command entry is one of the following command names: pg, more, or cat. The filename entry can be the name of one file, or a series of filenames separated by spaces. You may also use pattern-matching characters to specify your files. See Chapter 2 for information on using pattern-matching characters.

The pg command allows you to view one or more files. In the following example, the pg command displays the contents of file1 in your login directory:

$  pg file1

You start the vi program by entering
the command vi, optionally followed by the name
of a new or existing file.
$

To view the contents of both file1 and file2, enter both file names on the command line. When you display files that contain more lines than will fit on the screen, the pg command pauses as it displays each screen. To view the next screen of information in a file, press the Return key until you reach the end of the current file. When you press the Return key at the end of the current file, the start of the next file is displayed. The pg command always displays multiple files in the order in which you listed them on the command line. In the example shown below, (EOF): (end of file) means that you are at the end of the current file.

$  pg file1 file2 You start the vi program by entering
the command vi, optionally followed by the name
of a new or existing file.
(EOF):[Return]
(Next file: file2)[Return]
If you have created a new file, you will find
that it is easy to add text.
(EOF):[Return]
$ 

At the Next file: filename prompt, you can enter the -n option to go back to the previous file instead of displaying the next file.

When you display files that contain more lines than will fit on the screen, the pg command pauses as it displays each screen. To see the next screen of information in a file, press the Return key.

The more command also allows you to enter multiple file names on the command line and is very much like the pg command in the way that it handles long files. If the file(s) contains more lines than can fit on your screen, more pauses and displays a message telling you what percentage of the file you have viewed thus far. At this point, you can do one of the following:

• Press the Space bar to display the remainder of the file a page at a time

• Press the Return key to display one line at a time

• Type q to quit viewing the file(s)

The cat command also displays text. However, it is less useful for viewing long files because it does not paginate files. When viewing a file that is larger than one screen, the contents will display too quickly to be read. When this happens, press Ctrl/S to halt the display. You can then read the text. When you want to display the remainder of the file, press Ctrl/Q. Because cat is not useful for viewing long files, you may prefer using the pg or more command in these cases.

The pg, more, and cat commands all have additional options that you may find useful. For more information, refer to the reference pages for these commands.

3.2.2    Displaying Files with Formatting (pr)

Formatting is the process of controlling the way the contents of your files appear when you display or print them. The pr command displays a file in a simple but useful style.

Note

The pr command does not interpret any text formatting macros that may reside in your file. The pr command does not format files the same way as nroff or troff, for example.

To display a file with simple formatting, the format of the command is:

pr filename

The filename entry can be the name of the file, the relative pathname of the file, the full pathname of the file, or a list of filenames separated by spaces. The format you use depends on where the file is located in relation to your current directory. You may also use pattern-matching characters to specify files. See Chapter 2 for information on pattern matching.

Used without any options, the pr command does the following:

• Divides the contents of the file into pages

• Puts the date, time, page number, and filename in a heading at the top of each page

• Leaves five blank lines at the end of the page

When you use the pr command to display a file, its contents may scroll off your screen too quickly for you to read them. When this happens, you can view the formatted file by using the pr command along with the more command. The more command instructs the system to pause at the end of each screenful of text.

For example, to display a long file called report so that it pauses when the screen is full, enter the following command:

$  pr report | more

When the system pauses at the first screen of text, press the Space bar to display the next screen. The previous command uses the pipe symbol (|) to take the output from the pr command and use it as input to the more command. For more information on pipes, see Section 7.4.2.

Sometimes you may prefer to display a file in a more sophisticated format. You can use a number of flags in the command format to specify additional formatting features. Table 3-3 explains several of these flags.

Table 3-3: The pr Command Flags

You can use more than one flag at a time with the pr command. In the following example, you instruct pr to format file1 with these characteristics:

• With double spacing (d)

• With the title "My Novel" rather than the name of the file

$  pr -dh 'My Novel' file1

For detailed information about pr and its flags, refer to the pr(1) reference page.

3.3    Printing Files (lpr, lpq, lprm)

Use the lpr command to send one or more files to the system printer. The lpr command actually places files in a print queue, which is a list of files waiting to be printed. Once the lpr command places your files in the queue, you can continue to do other work on your system while you wait for the files to print.

The general format of the lpr command is:

lpr filename

The filename entry can be the name of the file, the relative pathname of the file, the full pathname of the file, or a list of filenames separated by spaces. The format you use depends on where the file is located in relation to your current directory. You may also use pattern-matching characters to specify files. See Chapter 2 for information on pattern matching.

If your system has more than one printer, use the following format to specify where you want the file to print:

lpr -P printername filename

The -P flag indicates that you want to specify a printer. The printername entry is the name of a printer. Printers often have names such as lp0, lp1, and lpn. Ask your system administrator for the printer names at your facility.

If your system has more than one printer, one of them is the default printer. When you do not enter a specific printername, your print request goes to the default printer.

The following example shows how to use the lpr command to print one or more files on a printer named lp0:

$  lpr -Plp0 file1
$  lpr -Plp0 file2 file3

$

The first lpr command sends file1 to the lp0 printer and then displays the shell prompt: a dollar sign ($). The second lpr command sends file2 and file3 to the same print queue, and then displays the shell prompt before the files finish printing.

Several lpr command flags enable you to control the way in which your file prints. Following is the general format for using a flag with this command:

lpr flag filename

Table 3-4 explains some of the most useful lpr command flags.

Table 3-4: The lpr Command Flags

Once you have entered the lpr command, your print request is entered into the print queue.

To see the position of the request in the print queue, use the lpq command. To look at the print queue, enter:

$  lpq

If your request has already been printed, or if there are no requests in the print queue, the system responds with the following message:

no entries

If there are entries in the print queue, the system lists them and indicates which request is currently being printed. Following is a typical listing of print queue entries (your listing will vary):

Rank   Owner      Job  Files                Total Size
active marilyn    489  report               8470 bytes
1st    sue        135  letter               5444 bytes
2nd    juan       360  (standard input)     969 bytes
3rd    larry      490  travel               1492 bytes

The lpqcommand displays the following for each print queue entry:

• Its priority

• Its owner

• Its job number

• Name of the file

• Size of the file in bytes

For example, Marilyn's report (job number 489) is currently being printed, and the requests of Sue, Juan, and Larry are pending.

When you print files, the position of the request in the queue as well as its size may help you estimate when your request may be finished. Generally, the higher the priority number in the queue and the larger the print request, the more time it will take.

If your system has more than one printer, use the following format to specify which print queue you want to see:

lpq -P printername filename

The -P flag indicates that you want to specify a print queue. The printername entry is the name of a particular printer. Use the lpstat -s command to learn the names of all the printers.

If you decide not to print your request, you can delete it from the print queue by using the lprm command. The general format of the lprm command is the following:

lprm jobnumber

The jobnumber entry specifies the job number that the system has assigned to your print request. You can see the job number by entering the lpq command.

For example, if Larry wants to cancel his print request, he can enter:

$  lprm 490

$

The travel file will be removed from the print queue.

3.4    Linking Files (ln)

A link is a connection between a filename and the file itself. Usually, a file has one link - a connection to its original filename. However, you can use the ln (link) command to connect a file to more than one filename at the same time.

Links are convenient whenever you need to work with the same data in more than one place. For example, suppose you have a file containing assembly-line production statistics. You use the data in this file in two different documents - in a monthly report prepared for management, and in a monthly synopsis prepared for the line workers.

You can link the statistics file to two different filenames, for example, mgmt.stat and line.stat, and place these filenames in two different directories. In this way, you save storage space because you have only one copy of the file. More importantly, you do not have to update multiple files. Because mgmt.stat and line.stat are linked, editing one automatically updates the other, and both filenames always refer to the same data.

3.4.1    Hard Links and Soft Links

There are two kinds of links available for your use: hard links and soft (symbolic) links.

• Hard links allow you to link only files in the same file system. When you create a hard link, you are providing another name for the same file. All the hard link names for a file, including the original name, are on equal footing. It is incorrect to think of one filename as the real name, and another as only a link.

• Soft links or symbolic links allow you to link both files and directories. In addition, you may link both files and directories across different file systems. A symbolic link is actually a distinct file that contains a pointer to another file or directory. This pointer is the pathname to the destination file or directory. Only the original filename is the real name of the file or directory. Unlike a hard link, a soft link is actually only a link.

With both hard and soft links, changes made to a file through one name appear in the file as seen through another name.

A major difference between hard and soft links occurs when removing them. A file with hard-linked names persists until all its names have been removed. A file with soft-linked names vanishes when its original name has been removed; any remaining soft links then point to a nonexistent file. See Section 3.4.5.

3.4.2    Links and File Systems

The term file system as used in this discussion of links differs from its earlier usage in this book. Previously, a file system was defined as a useful arrangement of files into a directory structure. Here, the same term acquires a more precise meaning: the files and directories contained within a single disk partition. A disk partition is a physical disk, or a portion of one, that has been prepared to contain file directories.

You can use the df command to discover the name of the disk partition that holds any particular directory on your operating system. Here is an example in which df shows that the directories /u1/info and /etc are in different file systems, but that /etc and /tmp are in the same file system:

$  df /u1/info

Filesystem 512-blks    used  avail capacity  Mounted on
/dev/rz2c    196990  163124  14166    92%    /u1

Filesystem 512-blks    used  avail capacity  Mounted on
/dev/rz3a     30686   19252   8364    70%    /

Filesystem 512-blks    used  avail capacity  Mounted on
/dev/rz3a     30686   19252   8364    70%    /
$

3.4.3    Using Links

To link files in the same file system, use the following command format:

ln /dirname1/filename1 /dirname2/filename2

The /dirname1/filename1 entry is the pathname of an existing file. The /dirname2/filename2 entry is the pathname of a new filename to be linked to the existing /dirname1/filename1. The dirname1 and dirname2 arguments are optional if you are linking files in the same directory.

If you want to link files and directories across file systems, you can create symbolic links. To create a symbolic link, add an -s flag to the ln command sequence and specify the full pathnames of both files. The ln command for symbolic links takes the following form:

ln -s /dirname1/filename1 /dirname2/filename2

The /dirname1/filename1 entry is the pathname of an existing file. The /dirname2/filename2 entry is a pathname of a new filename in a different file system.

In the following example, the ln command links the new filename checkfile to the existing file named file3:

$  ln file3 checkfile

$

Now use the more command to verify that file3 and checkfile are two names for the same file:

$  more file3

The system displays the following:

You will find that vi is a useful
editor that has many features.
$

Now display the text of checkfile:

$  more checkfile

You will find that vi is a useful
editor that has many features.
$

Notice that both file3 and checkfile contain the same information. Any change that you make to the file under one name will show up when you access the file by its other name. Updating file3, for example, will also update checkfile.

If your two files were located in directories that are in two different file systems, you need to create a symbolic link between them. For example, to link a file called newfile that is in the /reports directory to the file called mtgfile in the /summary directory, you can create a symbolic link by using the following:

$  ln -s /reports/newfile /summary/mtgfile

$

The information in both files is still updated in the same manner as previously explained.

3.4.4    How Links Work - Understanding Filenames and i-numbers

Each file has a unique identification number, called an i-number. The i-number refers to the file itself - data stored at a particular location - rather than to the filename. The i-number distinguishes the file from other files within the same file system.

A directory entry is a link between an i-number that represents a physical file and a filename. It is this relationship between files and filenames that enables you to link multiple filenames to the same physical file - that is, to the same i-number.

To display the i-numbers of files in your current directory, use the ls command with the -i (print i-number) flag in the following format:

ls -i

Examine the identification numbers of the files in your login directory. The number preceding each filename in the listing is the i-number for that file.

$  ls -i

1079 checkfile  1077 file1  1078 file2  1079 file3
$

The i-numbers in your listing will differ from those shown in this example. However, the important thing to note is the identical i-numbers for file3 and checkfile, the two files linked in the previous example. In this case, the i-number is 1079.

Because an i-number represents a file within a particular filesystem, hard links cannot exist between separate file systems.

The situation is entirely different with symbolic links, where the link becomes a new file with its own, new i-number. The symbolic link is not another filename on the original file's i-number, but instead is a separate file with its own i-number. Because the symbolic link refers to the original file by name, rather than by i-number, symbolic links work correctly between separate file systems.

3.4.5    Removing Links

The rm (remove file) command does not always remove a file. For example, suppose that a file is linked to more than one filename; that is, several names refer to the same i-number. In this case, the rm command removes the link between the i-number and that filename, but leaves the physical file intact. The rm command actually removes a physical file only after it has removed the last link between that file and a filename, as shown in Figure 3-1. When a symbolic link is removed, the filename specifying the pointer to the destination file or directory is removed.

For detailed information about the rm command, refer to Section 3.9.

Figure 3-1: Removing Links and Files

To display both the i-numbers and the number of filenames linked to a particular i-number, use the ls command with the -i (print i-number) and the -l (long listing) flags in the following format:

ls -il

Examine the links in your login directory. Remember that the i-numbers displayed on your screen will differ from those shown in the example and that your username and your group's name will replace the larry and system entries.

$  ls -il

total 3
1079 -rw-r--r-- 2 larry system   65 Jun 5 10:06 checkfile
1077 -rw-r--r-- 1 larry system  101 Jun 5 10:03 file1
1078 -rw-r--r-- 1 larry system   75 Jun 5 10:03 file2
1079 -rw-r--r-- 2 larry system   65 Jun 5 10:06 file3
1080 drwxr-xr-x 2 larry system   32 Jun 5 10:07 project
$

Again, the first number in each entry shows the i-number for that filename. The second element in each line shows the file permissions, described in detail in Chapter 5.

The third field for each entry, the number to the left of the username, represents the number of links to that i-number. Notice that file3 and checkfile have the same i-number, 1079, and that both show two links. Each time the rm command removes a filename, it reduces the number of links to that i-number by one.

In the following example, use the rm command to remove the filename checkfile.

$  rm checkfile

$

List the contents of the directory with the ls -il command. Notice that the rm command has reduced the number of links to i-number 1079, which is the same i-number to which file3 is linked, by one.

$  ls -il

total 3
1077 -rw-r--r-- 1 larry system  101 Jun 5 10:03 file1
1078 -rw-r--r-- 1 larry system   75 Jun 5 10:03 file2
1079 -rw-r--r-- 1 larry system   65 Jun 5 10:06 file3
1080 drwxr-xr-x 2 larry system   32 Jun 5 10:07 project
$

3.5    Copying Files (cp)

This section provides information about how to copy files on a local system. For information about copying files to and from remote systems see Chapter 12 and Chapter 14.

The cp (copy) command copies a file from one filename to another filename in your current directory or copies the file from one directory to another directory.

The cp command is especially useful to make backup copies of important files. Because the backup and the original are two distinct files, you can make changes to the original while still maintaining an unchanged copy in the backup file. This is helpful in case something happens to the original version. Also, if you decide you do not want to save your most recent changes to the original file, you can begin again with the backup file.

Compare the cp command, which actually copies files, with the ln command, which creates multiple names for the same file. Section 3.4 explains the ln command in detail. Refer also to the cp(1) and ln(1) reference pages.

The format of the cp command is:

cp source destination

The source entry is the name of the file to be copied. The destination entry is the name of the file to which you want to copy source. The source and destination entries can be filenames in your current directory or pathnames to different directories. This statement is true when you are copying files from one directory to another. To copy the contents of an entire directory to another directory (recursively, using the -r option), see Section 4.4.

To copy files to a different directory, use the general format of the cp command. In this case, source is a series of one or more filenames and destination is a pathname that ends with the name of the target directory. In the source entry you may also use pattern-matching characters.

3.5.1    Copying Files in the Current Directory

The cp command creates the destination file if it does not already exist. However, if a file with the same name as the destination file does exist, cp copies the source file over the existing destination file.

Caution

If the destination file exists, your shell may allow the cp command to erase the contents of that file before it copies the source file. As a result, be certain that you do not need the contents of the destination file, or that you have a backup copy of the file, before you use it as the destination file for the cp command. If you use the C shell, see Table 8-6 for the noclobber variable that can be set to prevent the erasure of the destination file.

In the following example, the destination file does not exist, so the cp command creates it. First, list the contents of your login directory:

$  ls

file1    file2    file3    project
$

Copy the source file, file2, into the new destination file, file2x:

$  cp file2 file2x

$

List the contents of the directory to verify that the copying process was successful:

$  ls

file1    file2    file2x   file3    project
$

3.5.2    Copying Files into Other Directories

You need a subdirectory to work through the following example, so create one called reports with the mkdir command:

$  mkdir reports

$

To copy the file2 file into the reports directory, enter:

$  cp file2 reports

$

List the contents of reports to verify that it contains a copy of file2:

$  ls reports

file2
$

You can also use the cp command to copy multiple files from one directory into another directory. The format of the command is:

cp filename1 filename2 dirname

In the following example, enter the cp command to copy both file2 and file3 into the reports directory, and then list the contents of that directory:

$  cp file2 file3 reports
$  ls reports

file2  file3
$

In the above example, you do not have to specify file2 and file3 as part of the dirname entry because the files being copied are retaining their original filenames.

You may also use pattern-matching characters to copy files. For example, to copy file2 and file3 into reports, enter:

$  cp file* reports

$

To change the name of a file when you copy it into another directory, enter the name of the source file (the original file), the directory name, a slash (/), and then the new filename. In the following example, copy file3 into the reports directory under the new name notes, and list the contents of the reports directory:

$  cp file3 reports/notes
$  ls reports

file2  file3  notes
$

3.6    Renaming or Moving Files (mv)

You can use the mv (move) command to perform the following actions:

• Move one or more files from one directory into another directory

• Rename files

The format of the mv command is:

mv oldfilename newfilename

The oldfilename entry is the name of the file you want to move or rename. The newfilename entry is the new name you want to assign to the original file. Both entries can be names of files in the current directory, or pathnames to files in a different directory. You may also use pattern-matching characters.

The mv command links a new name to an existing i-number and breaks the link between the old name and that i-number. It is useful to compare the mv command with the ln and cp commands, which are explained in Section 3.4 and Section 3.5. Refer also to the reference pages for these commands.

3.6.1    Renaming Files

In the following example, first list the i-number of each file in your current directory with the ls -i command. Next, enter the mv command to change the name of file file2x to newfile. The i-numbers displayed on your screen will differ from the numbers in the example:

$  ls -i

1077 file1    1088 file2x   1080 project
1078 file2    1079 file3    1085 reports

$

Again, list the contents of the directory:

$  ls -i

1077 file1    1079 file3    1080 project
1078 file2    1088 newfile  1085 reports
$

Note two things in this example:

• The mv command changes the name of file file2x to newfile.

• The i-number for the original file (file2x) and newfile is the same - 1088.

The mv command removes the connection between i-number 1088 and filename file2x, replacing it with a connection between i-number 1088 and filename newfile. However, the command does not change the file itself.

3.6.2    Moving Files into a Different Directory

You can also use the mv command to move one or more files from your current directory into a different directory.

Note

Type the target directory name carefully because the mv command does not distinguish between filenames and directory names. If you enter an invalid directory name, the mv command takes that name as a new filename. The result is that the file is renamed rather than moved.

In the following example, the ls command lists the contents of your login directory. The mv command moves file2 from your current directory into the reports directory. The ls command then verifies that the file has been removed:

$  ls

file1    file2    file3    newfile  project  reports

file1    file3    newfile  project  reports
$

List the contents of the reports directory to verify that the command has moved the file:

$  ls reports

file2  file3  notes
$

You may also use pattern-matching characters to move files. For example, to move file1 and file3 into reports, you could enter the following command:

$  mv file* reports

$

Now list the contents of your login directory to verify that file1 and file3 have been moved:

$  ls

newfile  project  reports
$

Copy file1, file2, and file3 back into your login directory. The dot (.) in the following command line specifies the current directory, which in this case is your login directory:

$  cp reports/file* .

$

Verify that the files are back in your login directory:

$  ls

file1    file2    file3    newfile  project  reports
$

Lastly, verify that file1, file2, and file3 are still in the reports directory:

$  ls reports

file1    file2    file3    newfile  project  reports
$

3.7    Comparing Files (diff)

You can compare the contents of text files with the diff command. Use the diff command when you want to pinpoint the differences in the contents of two files that are expected to be somewhat different.

The format of the diff command is:

diff file1 file2

The diff command scans each line in both files looking for differences. When the diff command finds a line (or lines) that differ, for each line that is different the following information is reported:

• Line numbers of any changes

• Whether the difference is an addition, a deletion, or a change to the line

If the change is caused by an addition, diff displays:

l[,l] a r[,r]

where l is a line number in file1 and r is a line number in file2. The a indicates an addition. If the difference was a deletion, diff would specify a d; if the difference was a change to a line, diff would specify a c.

The actual differing lines follow. In the leftmost column, a left angle bracket (<) indicates lines from file1, and a right angle bracket (>) indicates lines from file2.

For example, suppose that you want to quickly compare the following meeting rosters in the files jan15mtg and jan22mtg:

jan15mtg	jan22mtg
alice	alice
colleen	brent
daniel	carol
david	colleen
emily	daniel
frank	david
grace	emily
helmut	frank
howard	grace
jack	helmut
jane	jack
juan	jane
lawrence	juan
rusty	lawrence
soshanna	rusty
sue	soshanna
tom	sue
	tom

Instead of tediously comparing the list by sight, you can use the diff command to compare jan15mtg with jan22mtg as follows:

$  diff jan15mtg jan22mtg

2a3,4
> brent
> carol
10d11
< howard
$

Here we find that Brent and Carol attended the meeting on January 22, and Howard did not. We know this because the line number and text output indicate that brent and carol are additions to file jan22mtg and that howard is a deletion.

In cases where there are no differences between files, the system will merely return your prompt. For more information, see the diff(1) reference page.

3.8    Sorting File Contents (sort)

You can sort the contents of text files with the sort command. You can use this command to sort a single file or multiple files.

The format of the sort command is:

sort filename

The filename entry can be the name of the file, the relative pathname of the file, the full pathname of the file, or a list of filenames separated by spaces. You may also use pattern-matching characters to specify files. See Chapter 2 for information about pattern matching.

A good example of what the sort command can do for you is to sort a list of names and put them in collated order as defined by your current locale. For example, assume that you have lists of names that are contained in three files, list1, list2, and list3:

list1	list2	list3
Zenith, Andre	Rocca, Carol	Hamilton, Abe
Dikson, Barry	Shepard, Louis	Anastio, William
D'Ambrose, Jeanette	Hillary, Mimi	Saluccio, William
Julio, Annette	Chung, Jean	Hsaio, Peter

To sort the names in all three files, enter:

$  sort list*

Anastio, William
Chung, Jean
D'Ambrose, Jeanette
Dickson, Barry
Hamilton, Abe
Hillary, Mimi
Hsaio, Peter
Julio, Annette
Rocca, Carol
Saluccio, Julius
Shepard, Louis
Zenith, Andrew
$

You can also capture the sorted list by redirecting the screen output to a file that you name by entering:

$  sort list* >newlist

$

For more information about redirecting output, see Chapter 6. For a detailed description of the sort command and its many options, see the sort(1) reference page.

3.9    Removing Files (rm)

When you no longer need a file, you can remove it with the rm (remove file) command. Use this command to remove a single file or multiple files.

The format of the rm command is:

rm filename

The filename entry can be the name of the file, the relative pathname of the file, the full pathname of the file, or a list of filenames. The format you use depends on where the file is located in relation to your current directory.

3.9.1    Removing a Single File

In the following example, you remove the file called file1 from your login directory.

First, return to your login directory with the cd (change directory) command. Next, enter the pwd (print working directory) command to verify that your login directory is your current directory, and then list its contents. Remember that the system substitutes the name of your login directory for the notation /u/uname in the example.

$  cd
$  pwd

/u/uname

file1    file2    file3    newfile  project  reports
$

Enter the rm command to remove newfile, and then list the contents of the directory to verify that the system has removed the file.

$  rm newfile
$  ls

file1    file2    file3    project  reports
$

You must have permission to access a directory before you can remove files from it. For information about directory permissions, see Chapter 5.

Note

In addition to removing one or more files, rm also removes the links between files and filenames. The rm command actually removes the file itself only when it removes the last link to that file. For information about using the rm command to remove links, see Section 3.4.5.

3.9.2    Removing Multiple Files - Matching Patterns

You can remove more than one file at a time with the rm command by using pattern-matching characters. See Chapter 2 for a description of pattern-matching characters.

For example, suppose your current directory contains the following files: receivable.jun, payable.jun, payroll.jun, and expenses.jun. You can remove all four of these files with the rm *.jun command.

Caution

Be certain that you understand how the * pattern-matching character works before you use it. For example, the rm * command removes every file in your current directory. Be especially careful with * at the beginning or end of a filename. If you mistakenly enter rm * name instead of rm *name, you will remove all your files, rather than just those ending with name. (If your system is backed up on a regular basis, your system administrator can help you recover lost files.)

You may prefer to use the -i flag with the rm command, which prompts you for verification before deleting a file or files. See the end of this section for details.

You can also use the pattern-matching question mark (?) character with the rm command to remove files whose names are the same, except for a single character. For example, if your current directory contains the files record1, record2, record3, and record4, you can remove all four files with the rm record? command.

For detailed information about pattern-matching characters, see Chapter 2.

When using pattern-matching characters, you may find the -i (interactive) flag of the rm command particularly useful. The rm -i command allows you to selectively delete files. For each file selected by the command, the operating system asks whether or not you want to delete or retain the file.

For example, suppose that your directory contains the files record1, record2, record3, record4, record5, and record6. Create those files now in your login directory by using the touch command as follows:

$  touch record1 record2 record3 record4 record5 record6

$

The touch command is useful when you want to create empty files, as you are now. For complete information on the touch command, see the touch(1) reference page.

If you want to remove four of the six files that begin with the characters record, enter:

$  rm -i record?
rm: remove record1? n
rm: remove record2? y
rm: remove record3? y
rm: remove record4? y
rm: remove record5? y
rm: remove record6? n

$

In the preceding example, you have deleted all files except for record1 and record6.

Note

In addition to removing one or more files, the rm command also provides an option, the -r flag, that removes files and directories at the same time. See Chapter 4 for more information.

3.10    Determining File Type (file)

Use the file command when you want to see what kind of data a file contains without having to display its contents. The file command displays whether the file is one of the following:

• A text file

• A directory

• Input for one of the text formatting packages troff, nroff, or eqn input text

• Source code for the C or FORTRAN programming languages

• An executable file

The file command is especially useful when you suspect that a file contains a compiled program. Displaying the contents of a compiled program can produce disconcerting results on your screen.

The format of the file command is:

file filename

The filename entry can be the name of the file, the relative pathname of the file, the full pathname of the file, or a list of filenames. The format you use depends on where the file is located in relation to your current directory. You may also use pattern-matching characters to specify files. See Chapter 2 for information on pattern matching.

For example, to determine the file type of entries in your login directory, enter the following:

$  cd
$  pwd

/u/uname

file1:  ascii text
file2:  ascii text
file3:  ascii text
project:  directory
record1:  empty
record6:  empty
reports:  directory
$

The file command has identified file1, file2, and file3 as ASCII text files, project and reports as directories, and record1 and record6 as empty files.

For more information on the file command, see the file(1) reference page.