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Guide To UNIX Using Linux Third Edition. Chapter Four: UNIX/Linux File Processing. Objectives. Explain UNIX and Linux file processing Use basic file manipulation commands to create, delete, copy, and move files and directories

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Guide to unix using linux third edition

Guide To UNIX Using LinuxThird Edition

Chapter Four:

UNIX/Linux File Processing


Objectives
Objectives

  • 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

Guide to UNIX Using Linux, Third Edition


Objectives continued
Objectives (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Unix and linux file processing
UNIX and Linux File Processing

  • 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

Guide to UNIX Using Linux, Third Edition


Reviewing unix linux file types
Reviewing UNIX/Linux File Types

  • 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

Guide to UNIX Using Linux, Third Edition


Reviewing unix linux file types continued
Reviewing UNIX/Linux File Types (continued)

  • Special files

    • Character special files relate to serial I/O devices

    • Block special files relate to devices such as disks

Guide to UNIX Using Linux, Third Edition


Understanding file structures
Understanding File Structures

  • 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

Guide to UNIX Using Linux, Third Edition


Understanding file structures continued
Understanding File Structures (continued)

Guide to UNIX Using Linux, Third Edition


Processing files
Processing Files

  • 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)

Guide to UNIX Using Linux, Third Edition


Using input and error redirection
Using Input and Error Redirection

  • 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

Guide to UNIX Using Linux, Third Edition


Manipulating files
Manipulating Files

  • 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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued
Manipulating Files (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued1
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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued2
Manipulating Files (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued3
Manipulating Files (continued)

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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued4
Manipulating Files (continued)

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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued5
Manipulating Files (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Manipulating files continued6
Manipulating Files (continued)

Guide to UNIX Using Linux, Third Edition


Creating script files
Creating Script Files

  • 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

Guide to UNIX Using Linux, Third Edition


Creating script files continued
Creating Script Files (continued)

Guide to UNIX Using Linux, Third Edition


Using the join command on two files
Using the join Command on Two 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

Guide to UNIX Using Linux, Third Edition


A brief introduction to the awk program
A Brief Introduction to theAwk Program

  • 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

Guide to UNIX Using Linux, Third Edition


A brief introduction to the awk program continued
A Brief Introduction to theAwk Program (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Chapter summary
Chapter Summary

  • 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)

Guide to UNIX Using Linux, Third Edition


Chapter summary continued
Chapter Summary (continued)

  • 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

Guide to UNIX Using Linux, Third Edition


Chapter summary continued1
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

Guide to UNIX Using Linux, Third Edition


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