Guide To UNIX Using Linux Fourth Edition

Chapter Four

UNIX/Linux File Processing

Guide To UNIX Using Linux Fourth Edition

Chapter 4 (27 Slides) 1CTEC 110

• 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

Objectives


• Create a script file• Use the join command to link files using a

common field• Use the awk command to create a professional-

looking report

Objectives (continued)


• 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

UNIX and Linux File Processing


• 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

Reviewing UNIX/Linux File Types


• Special files– Character special files relate to serial I/O devices– Block special files relate to devices such as disks

Reviewing UNIX/Linux File Types (continued)


• 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

Understanding File Structures



• 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)

Processing Files


• 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

Using Input and Error Redirection


When you manipulate files, you work with the files themselves, as well as their contents

Create files using output redirection

◦ cat command - concatenate text via output redirection

◦ without a command - > filename

◦ touch command - creates empty files

Manipulating Files


• 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

• 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

Manipulating Files (continued)


• Move files from directory to directory

– mv command - removes file from one directory and places it in another

• Finding a file helps you locate it in the directory structure

– find command - searches for the file that has the name you specify



• 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




The paste command joins text of different files in side by side fashion

Extracting fields of a file using output redirection: the cut command removes specific columns or fields from a file


• 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




• 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

Creating Script Files



• 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

Using the join Command on Two Files


• 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

A Brief Introduction to theAwk Program


• 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


A Brief Introduction to theAwk Program (continued)

• 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)

Chapter Summary


• 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

Chapter Summary (continued)


• 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 Summary (continued)


• 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 Unix Exercises


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Guide To UNIX Using Linux Fourth Edition