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intro unix/linux 06
 

intro unix/linux 06

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using utilities to accomplish complex tasks

using utilities to accomplish complex tasks

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    intro unix/linux 06 intro unix/linux 06 Presentation Transcript

    • Lesson 6-Using Utilities to Accomplish Complex Tasks
    • Overview
      • Creating and executing a script to list user information.
      • Listing directories and files separately.
      • Identifying changes made to files in a directory.
      • Creating a complex script.
    • Creating and Executing a Script to List User Information
      • Creating a script.
      • Executing a script.
    • Creating a Script
      • A series of commands can be executed repeatedly/automatically by placing them in a script file.
      • Placing commands in scripts helps avoid errors and save time.
      • The vi editor can be used to create a file.
      • The ":wq" commands are used to write to a file and return to the shell.
    • Executing a Script
      • The commands in a file can be executed in two ways:
        • Instructions can be given to the current shell to read the file (source) and execute all the commands.
        • The script file can be made executable, and a child shell can be started to read the script file and execute the commands.
    • Executing a Script
      • The command used to make the shell executable is “chmod +x filename”.
      • By default, the output of the script is redirected to the screen.
      • The output of the script can be redirected to a file.
    • Listing Directories and Files Separately
      • Selecting only directories / files:
        • The “ls –F | grep /” command is used to select only lines that contain directory names.
        • The “ls –F | grep / | column” command can be used to put the output into columns.
        • The “ls –F | grep –v / | column” command is used to select only files.
    • Listing Directories and Files Separately Selecting Directories Using Multiple Utilities
    • Listing Directories and Files Separately Interpretation by grep Using –v option
    • Listing Directories and Files Separately
      • Adding comments to scripts:
        • The # (pound) sign is used to add comments to scripts.
        • Ensure that the # sign is placed at the beginning of each line.
        • The pound (#) sign cannot be used inside a long command line.
    • Identifying Changes Made to Files in a Directory
      • Collecting data about files in a directory:
        • The “ls –l directory name” command can be used to provide information about the files in a particular directory.
        • The output of the code can also be redirected to another file by the command "ls -l directoryname > filename”.
        • The information includes the current status of each file, such as permissions, date of modification, owner, etc.
    • Identifying Changes Made to Files in a Directory
      • Comparing file information:
        • The “comm” command is used to identify the common aspects between two files.
        • It requires two arguments – the names of the two the files that are to be compared.
        • The command gives three columns of output – lines unique in the first file, lines unique in the second file, and lines in common.
    • Identifying Changes Made to Files in a Directory
      • Comparing file information:
        • The “diff” command is used to identify the differences between two files.
        • It requires two arguments – the names of the two files to be compared.
        • The command gives three columns of output – lines unique in the first file, lines unique in the second file, and lines common to the two files.
    • Creating a Complex Script
      • Determining the number of unique words in a file.
      • Removing punctuation.
      • Converting characters to lowercase.
      • Putting each word on a line.
      • Removing blank lines.
      • Sorting the lines.
    • Determining the Number of Unique Words in a File
      • The “uniq” utility is used to:
        • Provide a list of unique words in a file.
        • The number of times that each word is used.
        • The number of unique words.
    • Determining the Number of Unique Words in a File
      • The uniq utility outputs both, unique lines as well as single copies of any lines that are duplicate and adjacent.
      • The utility deletes identical lines.
      • The uniq utility deletes only those lines that are identical and adjacent.
    • Determining the Number of Unique Words in a File
      • The following things must be ensured for the uniq utility to work properly:
        • Punctuation and blank lines must be removed.
        • Differences in case for the same word must be reconciled.
        • The words must be one word to a line in a sorted order.
    • Removing Punctuation Shell and Utility Interpretation
    • Converting Characters to Lowercase Shell and tr Interpretation
    • Putting Each Word on a Line
      • To remove duplicate words using the uniq utility, the data must be modified to ensure that each word is on a line by itself.
      • The new line character “ ” is used to separate lines in a file.
      • The ASCII character code 012 can also be used to separate lines in a file.
    • Putting Each Word on a Line
      • The “man ascii” command is used to examine the ASCII characters and their associated codes.
      • TAB characters can also be replaced with new line characters.
    • Putting Each Word on a Line Using tr Utility to Replace Characters
    • Removing Blank Lines A View from the Shell
    • Sorting the Lines
      • The “sort” command can be used to sort the output such that all lines containing the same word are on adjacent lines.
      • The “uniq –c” command can be used to remove all duplicate lines.
      • The “sort –rn” command can be used to list the most frequently used words first.
    • Summary
      • A series of commands placed in a script file can be repeatedly executed, avoiding errors and saving time.
      • The ls utility provides a list of all the files and subdirectories in the current directory.
      • The # sign is used to add comments to script files.
      • The pipeline feature of UNIX is very useful and is central to manipulating data effectively with UNIX utilities.