Which of the following commands can be used to read the entire contents of a file?
Unix Tutorial #3: Reading Text Files¶Note Show
Topics covered: File manipulation, redirection, streams, stdin, stdout, stderr Commands used: cat, less, head, wc The command line is useful for both viewing and manipulating text files. Manipulation means editing text - for example, replacing words in text files, or appending text from the command line to the end of a file (also known as redirection). This is useful for creating scripts, text files containing one or more commands that are run consecutively. In later tutorials, you will use these techniques to automate your analyses, which can save enormous amounts of time. You can display the contents of a file using the Using the command line and the GUI to read the contents of a text file. On the left is the command line using the We refer to the output from this command as stdout, or standard output. The commands that are typed into the Terminal are called stdin, or standard input. This touches on the concept of streams, or the flow of information into and out of the command line, and we will use these ideas to give us more flexibility in manipulating text files. For now, think of stdin as anything you type into the Terminal, and stdout as what is returned if the command is run without any errors. If the command that you type does result in an error - for example, because the command was misspelled or because not enough arguments were provided - the text that is output to the Terminal is called stderr, or standard error. Illustration of streams in Unix. Whatever is typed into the Terminal is stdin, and, if it runs without error, whatever is output is called stdout. If there is an error, the output is instead called stderr. The Would return the first five lines; whereas typing Would return the last five lines. Although the default is to return five lines, these commands have an option to display any amount of lines that you choose. For example, head -10 myFile.txt tail -10 myFile.txt Would return the first ten lines and the last ten lines. Try these out yourself, changing the number of lines that are displayed. Redirection¶In addition to displaying the results of a command, stdout can be used to move or append the output to a file, a concept known as redirection. For example, if you type The word “sixteen” goes into the file tmp.txt instead of being written to standard output. Notice that it creates the file tmp.txt even if it doesn’t exist. However, if we try that again with another string - for example, It will overwrite the file with whatever we printed to standard output. If you want to append standard output to the end of a file without overwriting the other data in the file, use two greater-than signs. For example, type If you type Although these examples are trivial, redirection is invaluable for quickly editing text files and for writing scripts, which allow you to run analyses for hundreds or thousands of subjects with only a few lines of code. Video¶Click
here for a video walkthrough of commands for reading text files. This video will also show you how to read help files using the Exercises¶
In your own words, explain the difference between the two methods. Which of the following commands can be used to read the entire contents of a file as a string using the file object obj?Explanation: read function is used to read all the lines in a file. 7.
Which of the following function is used to read the contents of file into a list variable?readlines() is used to read all the lines at a single go and then return them as each line a string element in a list. This function can be used for small files, as it reads the whole file content to the memory, then split it into separate lines.
Which of the following command is used to read the next line from a file?We can use the read command to read the contents of a file line by line.
Which of the following method can be used to open a file in file handling?Opening a file
The fopen() function is used to create a file or open an existing file: fp = fopen(const char filename,const char mode); There are many modes for opening a file: r - open a file in read mode.
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