String-Manipulation

• STRING MANIPULATION : Play with strings

  1. strings : used to extract readable text strings from binary files. When you run strings on a file, it scans through the binary data looking for sequences of printable characters and displays them. This is often useful for extracting human-readable information from compiled executables or other binary files.

     strings data.txt

  2. env : Environment variables in Linux are dynamic values that can affect the behavior of processes and programs running in the operating system.

     # display env variables
     
     $ env
     
     $ echo $PATH
     
     /usr/local/sbin:/usr/local/bin:/usr/sbin:/bin
     
     # This returns a list of paths separated by a colon that your system searches when it runs a command.
     
     # Modify the path variable 
     
     export PATH=$PATH:/path/to/new/directory
     

  3. cut : It is used for cutting out sections from each line of a file or from piped data.

     • c, --characters=LIST: Select only these characters.
     • f, --fields=LIST: Select only these fields.
     • d, --delimiter=DELIM: Use DELIM instead of TAB for field delimiter.

     # Extract 5th character from each line
     cut -c 5 sample.txt
     
     # Extract characters 3-7 and 12-16 from each line of a file:
     cut -c 3-7,12-16 filename.txt
     
     # Extract the first and third fields (using a comma as the delimiter) from a file
     # By default it 'd' is TAB
     cut -f 1,3 -d , filename.csv
     
     # Extract the second field (using a comma as the delimiter) from 
     # the output of another command:
     echo "John,Doe,25" | cut -f 2 -d ,

  4. head : By default the head command will show you the first 10 lines in a file.

     • The -n flag stands for number of lines.

     head -n 15 /var/log/syslog # diaplay first 15 lines
     head -c 15 /var/log/syslog # display first 15 characters
     

  5. tail : It is similar to head command as it prints the last 10 lines of a file

     tail -3 filename # display last 3 lines 
     tail +3 filename # skips first 2 lines 

  6. paste : The paste command is similar to the cat command, it merges lines together in a file.

     • EXAMPLES

     # Display the first 5 lines (head) and the last 5 lines (tail) of a file
     paste <(head -n 5 filename.txt) <(tail -n 5 filename.txt)
     
     # Display the first 3 lines (head) and the last 3 lines (tail) of the ls command
     paste <(ls | head -n 3) <(ls | tail -n 3)

  7. expand : To converts your TABs to spaces, use the expand command.(it doesn’t remove space).

  8. unexpand : Opposite of expand

     expand sample.txt > result.txt
     unexpand -a result.txt
     
     tr -s '\t' ' ' < input.txt > output.txt #It will reove tabs & make a single space
     tr -s '\n' ' ' < sample.txt # This change the newline into a space 
     tr -s ';' ' ' < sample.txt # This will change semicolon to space
     
     **NOTE- This will not change them temporarily, you need to save the output**

  9. sort : sort a file

     • -r, --reverse: Reverse the result of comparisons.
     • -n, --numeric-sort: Sort numerically.
     • -u, --unique: Output only unique lines.

     sort filename.txt
     
     # sort the file and '-m' merge the file 
     sort -m file1.txt file2.txt file3.txt > sorted_output.txt
     

  10. tr : The tr (translate) command allows you to translate a set of characters into another set of characters.

      tr a-z A-Z # coverts the lowecase to uppercase
      
      hello
      
      HELLO
      
      echo "123abc456" | tr -d '0-9' # Delete digits from string

  11. split : This will split it into different files, by default it will split them once they reach a 1000 line limit.

      # his splits input.txt into files each containing 100 lines.
      split -l 100 input.txt
      
      -l NUMBER: Split the file into chunks of NUMBER lines.
      -b SIZE[K|M|G]: Split the file into chunks of specified size.

  12. join : The join command allows you to join multiple files together by a common field:

      $ join -1 2 -2 1 file1.txt file2.txt
      
      1 John Doe
      
      2 Jane Doe
      
      3 Mary Sue

  13. uniq : The uniq (unique) command is another useful tool for parsing text.

      uniq reading.txt # remove duplicates
      
      uniq -c reading.txt # get the count of how many occurrences of a line
      
      uniq -u reading.txt # get unique values (occur only one time)
      
      uniq -d reading.txt # get duplicate values
      
      **Note** : uniq does not detect duplicate lines unless they are adjacent.
      
      # To overcome this limitation of uniq we can use sort in combination with uniq:
      sort reading.txt | uniq

  14. wc : The wc command stands for "word count" and is used to count the number of lines, words, and characters in a file.

      wc myfile.txt
      
      -l: Count lines.
      -w: Count words.
      -c: Count characters.

  15. nl : used to number lines in a file

      $ nl file1.txt
      
      1. i
      2. like
      3. turtles

Additional resource

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