Chapter Four
UNIX/Linux File
Processing
Guide To UNIX Using Linux
Fourth Edition
Chapter 4 (27 Slides)
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Objectives
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Explain UNIX and Linux file processing
Use basic file manipulation commands to create,
delete, copy, and move files and directories
Employ commands to combine, cut, paste,
rearrange, and sort information in files
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Objectives (continued)
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Create a script file
Use the join command to link files using a
common field
Use the awk command to create a professionallooking report
Chapter 4 (27 Slides)
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UNIX and Linux File Processing
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Based on the approach that files should be treated
as nothing more than character sequences
Because you can directly access each character,
you can perform a range of editing tasks – this
offers flexibility in terms of file manipulation
Chapter 4 (27 Slides)
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Reviewing UNIX/Linux
File Types
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Regular files, also known as ordinary files
– Create information that you maintain and
manipulate, and include ASCII and binary files
Directories
– System files for maintaining file system structure
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Reviewing UNIX/Linux
File Types (continued)
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Special files
– Character special files relate to serial I/O
devices
– Block special files relate to devices such as disks
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Understanding File Structures
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Files can be structured in many ways depending on
the kind of data they store
UNIX/Linux store data, such as letters and product
records, as flat ASCII files
Three kinds of regular files are
– Unstructured ASCII character
– Unstructured ASCII records
– Unstructured ASCII trees
Chapter 4 (27 Slides)
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Chapter 4 (27 Slides)
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Processing Files
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UNIX/Linux processes commands by receiving
input from a standard input device (e.g.
keyboard) and sending it to a standard output
device (e.g. monitor)
System administrators and programmers refer to
standard input as stdin, standard output as
stdout
When UNIX/Linux detect errors, they send data to
standard error (stderr, the monitor)
Chapter 4 (27 Slides)
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Using Input and Error Redirection
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You can use redirection operators to retrieve input from
something other than the standard input device and
send output to something other than the standard
output device
Examples of redirection
– Redirect the ls command output to a file, instead
of to the monitor (or screen)
– Redirect a program that receives input from the
keyboard to receive input from a file instead
– Redirect error messages to files, instead of to the
screen by default
Chapter 4 (27 Slides)
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Manipulating Files
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When you manipulate files, you work with the files
themselves, as well as their contents
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Create files using output redirection
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cat command - concatenate text via output
redirection
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without a command - > filename
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touch command - creates empty files
Chapter 4 (27 Slides)
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Manipulating Files (continued)
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Delete files when no longer needed
– rm command - permanently removes a
file or an empty directory
– The -r option of the rm command will
remove a directory and everything it
contains
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Copy files as a means of back-up or as a means to
assist with new file creation
– cp command - copies the file(s) specified
by the source path to the location
specified by the destination path
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Manipulating Files (continued)
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Move files from directory to directory
– mv command - removes file from one
directory and places it in another
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Finding a file helps you locate it in the directory
structure
– find command - searches for the file that
has the name you specify
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Manipulating Files (continued)
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Combining files using output redirection
– cat command - concatenate text of
two different files via output
redirection
– paste command - joins text of
different files in side by side fashion
Chapter 4 (27 Slides)
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The paste command joins text of different files in
side by side fashion
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Extracting fields of a file using output redirection: the
cut command removes specific columns or fields from
a file
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Manipulating Files (continued)
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Sorting the contents of a file
– sort command - sorts a file’s contents
alphabetically or numerically
– the sort command offers many options:
▫ You can sort the contents of a file and
redirect the output to another file
▫ Utilizing a sort key provides the option
of sorting on a field position within each
line
Chapter 4 (27 Slides)
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Chapter 4 (27 Slides)
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Creating Script Files
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UNIX/Linux users create shell script files to
contain commands that can be run sequentially
as a set – this helps with the issues of command
automation and re-use of command actions
UNIX/Linux users use the vi editor to create
script files, then make the script executable using
the chmod command with the x argument
Chapter 4 (27 Slides)
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Chapter 4 (27 Slides)
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Using the join Command on Two Files
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Sometimes you want to link the information in
two files
The join command is often used in relational
database processing
The join command associates information in
two different files on the basis of a common
field or key in those files
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A Brief Introduction to the
Awk Program
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Awk, a pattern-scanning and processing language
helps to produce professional-looking reports
Awk provides a powerful programming
environment that can perform actions on files that
are difficult to duplicate with a combination of
other commands
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A Brief Introduction to the
Awk Program (continued)
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Awk checks to see if the input records in
specified files satisfy a pattern
If so, awk executes a specified action
If no pattern is provided, awk applies the action
to every record
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Chapter Summary
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UNIX/Linux supports regular files, directories,
and character and block special files
File structures depend on data being stored
UNIX/Linux receives input from the standard
input device (keyboard, stdin) and sends output
to the standard output device (monitor, stdout)
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Chapter Summary (continued)
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touch updates a file’s time and date stamps and
creates empty files
rmdir removes empty directories
cut extracts specific columns or fields from a file
paste combines two or more files
sort sorts a file’s contents
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Chapter Summary (continued)
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To automate command processing, include
commands in a script file
join extracts data from two files sharing a
common field and uses this field to join the two
files
Awk is a pattern-scanning and processing
language useful for creating a formatted report
with a professional look
Chapter 4 (27 Slides)
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Chapter 4 Unix Exercises
• Work through Hands-on Projects
at end of chapter 4
• Canvas: Review Questions 4
– (Do not do questions 22,23,24 and 25)
• Read chapter 5 before next class session
• Quiz 4 Unix…
Chapter 4 (27 Slides)
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