Processing_text.sh

# #### Here we`ll learn how process and filter texts  ####

# cat is for display files content on your screen .
  # Example ->
    cat file.txt
    cat -s file.txt # do not display repeated blank empty text file lines.
    cat -v file.txt # display nonprinting charachters.
    cat -T file.txt # display a ^I when a tab character is encounter
    cat -n file.txt # number all text file lines and display that number in the output

# paste command to join together files side-by-side 
    #Example -> 
        paste file1.txt file2.txt

# od command to show file text content in octal
    #Example ->
        od file.txt

# split command to divide up file using size,bytes,lines. useful for split large log files
    #Example ->
        split -l 5 file.txt  splitedfile      

# sort command to sort file content without no change in origin file  
    #Example ->
        sort aplpha.txt
        sort -n aplpha.txt # sort number content . 
        sort aplpha.txt -o newfile.txt # sort content and save result in newfile.txt

# sort command to sort file content without no change in origin file  
    #Example ->
        sort aplpha.txt
        sort -n aplpha.txt # sort number content . 
        sort aplpha.txt -o newfile.txt # sort content and save result in newfile.txt

# nl command for show file content with line number 
    #Example ->
        nl file.txt     # add numbers to non-blank lines.
        nl -ba file.txt # adds number to all text file lines 

# more command is a utility for read through a large text file is by using a pager 
    #Example ->
        more file.txt
    #Note ->
        # Move forward (one page down) text file by pressing the spacebar 
        # Move forward (one line) text file by pressing the enter 
        # You can't move backward through a file . 
        # To exit from the more pager . press q key

# less command is a utility for read through a large text file is by using a pager 
    #Example ->
        less file.txt
    #Note ->
        # Move forward (one page down) text file by pressing the spacebar 
        # Move backward (one page up) text file by pressing the ESC+v 
        # Move forward (one line) text file by pressing the down arrow
        # Move forward (one line) text file by pressing the up arrow   
        # Search backward entire file by pressing the ? key
        # Search forward entire file by pressing the / key
        # To exit from the more pager . press q key

# head command displays the first 10 lines of text file . 
    #Example ->
        head file.txt
        haed -2 file.txt # display the first 2 lines of text file . 
       
# tail command displays the last 10 lines of text file . 
    #Example ->
        tail file.txt
        tail -n 20 file.txt # display the last 20 lines of text file .
        tail -n +43 file.txt # shows text lines from line number 43 of text file.
        tail -f file.txt # follows file changes , if new log writes to end of file tail will be show in live mode 
    #NOTE ->
        # to watch messages beging added to the journal file , use the journalctl --follow command . 
        journalctl --follow

# wc command display the file's number of lines , words , bytes in that order  
    #Example ->
        wc file.txt
        wc -l file.txt # display the file's number of lines
        wc -m file.txt # display the file's number of chars
        wc -w file.txt # display the file's number of words

# cut command helps to quickly extract small data sections from large text file. 
    #Example ->
        cut -d ":" -f 1,7 file.txt # filterss text file then show records have ":" delimiter and are part of field 1,7 
    #NOTES 
        # -f display only the record's fields denoted by flist 
        # -d designate the record's field delimiter as d . 

# uniq command will find repeated text lines only they come right after one another.
    #Example ->
        uniq file.txt  


# grep command one of the wonderful tool for sifting text 
    #Example ->
        grep "hello" file.txt # find lines have that hello word 
        grep -c "hello" file.txt # display a count of text file records that contain a pattern match 
        grep -i "hello" file.txt # ignore the case in the pattern as well as in text file.
        grep -r "hello" /home/*  # search directory's contents and for any subdirectory.
        grep -v "hello" /home/*  # display only files records that do not contain a pattern match 
        grep -rnw . -e "regex.*"  # search all current directory and subdirectory files and will be find lines have contain a pattern (regex) match  
        grep -f accounts.txt /etc/passwd #  take PATTERNS from accounts.txt
        grep -v ^$ file.txt # display only lines with text (filter out the blank lines) 
        grep -e "^root|^dbus" /etc/passwd # with ERE search the /etc/passwd file and find which lines start with root or dbus
    # NOTE 
        # grep support special group of bracket expression are character classes. 
            #Example ->
                grep [[:alnum:]] file.txt # matches any alphanumeric characters
                grep [[:alpha:]] file.txt # matches any alphabetic characters
                grep [[:digit:]] file.txt # matches any numeric characters
                grep [[:punct:]] file.txt # matches punctuation characters (!,#,$,@)

# sed command is stream editor. The sed utility edits a stream of text data based on a set of commands you supply ahead of time . 
    #Example ->
        echo "I love windows os and windows users "  | sed 's/windows/linux/'
             # The sed command receive string from echo and find  the windows  word and replace it with the linux word
             # The sed command just finds and replace the first occurrence of the word windows

        echo "I love windows os and windows users "  | sed 's/windows/linux/g'
             # The sed command receive string from echo and find the windows word and replace it with the linux word
             # The sed command finds and replace all of the windows word
        
        sed 's/love/like/' sed.txt 
             # The sed command replaces all the love word with the like word and print it without modify orginal file 

        sed '/love/d' sed.txt 
             # The sed.txt file line that contains the word love is not displayed to output . it was deleted in the output , but still exist within the text file

        sed -e 's/love/like ; s/boy/girl/' sed.txt
             #  The -e option allows you to employ multiple scripts in the sed command 
             #  The sed command replaces the love word with the like word and also replace the boy word with the girl word and this both commands processed with together in same time