In this tutorial we will be showing how to work with files stored in the host, such as reading the contents of the file, adding more lines, etc.

Listed below are few of the syntax used in Python to work with files. We will be using them in the Python scripts posted later:

• Open file in read mode
  theFile = open(‘myFile.txt’, r)
• Open file in append mode
  theFile = open(‘myFile.txt’, a)
• Open file in write mode
  theFile = open(‘myFile.txt’, r+)

• Read the entire file
  theFile.read()
• Read 4 bites of the file
  theFile.read(4)
• Read file line by line
  theFile.readline
• Read all lines in the file to a list
  theFile.readlines

• Write string to a file
  theFile.write(<string>)
• Closes the conenction to a file
  theFile.close()

Let us work with the files now:

• Now let us create a simple text file with the following content:
  [root@gw16-lap-devops webapp]# cat sample.txt
  Line 1
  Line 2
  Line 3
  Line 4
  Line 5
  Line 6
  Line 7

 

• Let us write a Python script to read and print the contents of the file:
  [root@gw16-lap-devops webapp]# cat readFile.py
  #! /usr/bin/python
  #
  myFile = open(“sample.txt”)
  print(myFile.read())
  myFile.close()

 

• Now if you run the file you will see the entire contents getting displayed.
  See if you can use the “myFile.read(8)” command in it and check the result.

Let us write a Python script to write a line to the same file and then read and print the contents of the file:

• [root@gw16-lap-devops webapp]# cat writeLines.py
  #! /usr/bin/python
  #
  theFile = open(“sample.txt”,’a’)
  theString = ‘\nAdding a line’
  theFile.write(theString)
  theFile.close()
  #
  myFile = open(“sample.txt”)
  print(myFile.read())
  myFile.close()

Let us write a Python script to write a line to the same file and then read and print the contents of the file:

• [root@gw16-lap-devops webapp]# cat writeLines.py
  #! /usr/bin/python
  #
  theFileName = ‘sample.txt’
  myFile = open(theFileName)
  theFileList1 = myFile.readlines()
  myFile.close()
  totalLines=len(theFileList1)
  #
  #
  theFile = open(theFileName,’a’)
  lineNo = totalLines + 1
  for i in range(3):
  theString = “Line ” + str(lineNo) + “\n”
  theFile.write(theString)
  lineNo = lineNo + 1
  theFile.close()
  #
  #
  myFile1 = open(theFileName)
  print(myFile1.read())
  myFile1.close()