Guide To UNIX Using Linux Third Edition Chapter Four: UNIX/Linux File Processing Guide To UNIX Using Linux Third Edition

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) 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 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 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) 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 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) Guide to UNIX Using Linux, Third Edition

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 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 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) 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 (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 (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 (continued) The paste command joins text of different files in side by side fashion Guide to UNIX Using Linux, Third Edition

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 (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 (continued) Guide to UNIX Using Linux, Third Edition

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) Guide to UNIX Using Linux, Third Edition

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 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) 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 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) 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 (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