intro unix/linux 06
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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.