sed command

• Basics

  -- Replace all 'foo' with 'bar' globally.
  $ sed -i 's/foo/bar/g' <filename>
      
  -- print line from 4 through 15
  $ sed -n '4,15p' <file name>
      
  -- exclude lines from 10 through 15
  $ sed '10,15d' <file-name>
      
      
  -- Display lines from different ranges
  $ sed -n -e '10,15p'-e '25,35p' <file-name>
      
  -- display content of a file after replacing a word
  $ sed 's/<word>/<new-word>/g' <file-name>
      
  -- replacing a word in a file
  $ sed -i 's/<word>/<new-word>/g' <file-name>
      
      
  -- replace a word and ignore case
  $ sed -i 's/<word>/<new-word>/gi' <file-name>
  

  -- Replace a word or characters in a range
  $ sed '30,50 s/<word>/<new-word/g'
  $ sed -i '30,50 s/<word>/<new-word/g'
      
  -- swiching multiple matches
  $ sed -i 's/ \(.*\):\(.*\)/\2, \1 /g'
      
      
  -- Replacing words only if seperate match is found.
  $ sed '/<pattern>/ s/<word>/<new-word>/g' msg.txt
      
  -- multiple replacements
  $ sed -i 's/that/this/gi;s/line/verse/gi' myfile.txt
  

• Ref: https://www.tecmint.com/linux-sed-command-tips-tricks/

AWK command

• Awk basic usage

  Awk can take the following options:
      
  -F fs     To specify a file separator.
  -f file     To specify a file that contains awk script.
  -v var=value     To declare a variable.
  

  $ awk 'pattern {action}' input-file > output-file
      
  -- print 5th column from lines those match the pattern
  $ awk 'word {print $5}' input-file
      
      
  -- seperate by field(-F) and print 2nd column
  $ awk -F, '{print $2}'
      
  -- If fieds are numbers, aws can run commands on them
  $ awk '{ print ($2 * $3) + $7 }' input-file
      
  -- Replace second field
  $ echo "Hello Tom" | awk '{$2="Adam"; print $0}'
  Hello Adam
  $
  

  ---

• Awk Preprocessing

  -- Print first line "The File Contents" followed by content of the file.
  $ awk 'BEGIN {print "The File Contents:"}
  {print $0}' myfile
      
  -- prints first line and last line in between file's content
  $ awk 'BEGIN {print "The File Contents:"}
      {print $0}
      END {print "File footer"}' myfile
  

  -- Count number of lines in a file
   $ awk 'BEGIN {count=0;} {print $0; var++;} END {print count}' <filename>
       
  -- 
  

• Awk built-in variables

  FIELDWIDTHS     Specifies the field width.
  RS     Specifies the record separator.
  FS     Specifies the field separator.
  OFS  Specifies the Output separator.
  ORS  Specifies the Output separator.
  

• Awk Arrays

  $ awk 'BEGIN
          {
              array["key1"]="value1"; 
              array["key2"]["subkey1"]="subvalue1";
                  
              print array["key1"];
              print array["key2"]["subkey1"];
          }'
              
  -- tp delete array element
  $ awk 'BEGIN
          {
              array["key"]="value"
              print array["key"]
                  
              delete array["key"]
                  
              # Below line prints nothing.
              print array["key"]
              
          }'
              
              
  -- Default value of array[key] is 0, when used in aithmatic operations
  $ awk 'BEGIN {array["key"]++; print array["key"]}'   
  1
  Ref here : https://www.gnu.org/software/gawk/manual/html_node/Uninitialized-Subscripts.html#Uninitialized-Subscripts
  

• Multidimentional Arrays in Awk

  $ awk 'BEGIN {vector["a", "aa"] = "Hello World!";  print vector["a", "aa"]}'
      
  

• Sorting Arrays

  Ref: https://www.gnu.org/software/gawk/manual/html_node/Controlling-Scanning.html#Controlling-Scanning
  

  Note: Semicolon(;) is not required if one line is standalone statement. Semicolon is needed to sperate multiple statements in one line.

Ref:

https://likegeeks.com/awk-command/

https://www.lifewire.com/write-awk-commands-and-scripts-2200573

https://www.gnu.org/software/gawk/manual/html_node/Arrays.html#Arrays