The dash (" -") tells ed to read from the standard input, and the < operator directs our script to that input. We can issue this script to ed with the following command, telling it to overwrite our original file. Now our script, when issued to ed, makes the changes and write the changes to disk. She loved chocolate chip cookies more than anything. She would look up into the clouds and dream of being a world-famous baker. Now, we can check to see that our script has changed by running the cat command again: cat my-ed-script.txt 5c It redirects output to a file, but instead of overwriting the destination file, it appends to the end of the file.) The command looks like this: echo "w" > my-ed-script.txt (The > operator is similar to the > operator. We can add this to our script by echoing the letter " w" and using the > operator to add it to our file. All that's missing from the script is the w command, which writes the changes. There's still one thing missing, though: we need the script to tell ed to actually write the file. we see the same script we saw displayed above. If we now check the contents of my-ed-script.txt with the cat command. If my-ed-script.txt doesn't exist, it is created if it exists already, it is overwritten. This command does not display anything on the screen (unless there is an error) instead, the output is redirected to the file my-ed-script.txt. operator, like this: diff -e file1.txt file2.txt > my-ed-script.txt Now let's see what it looks like when diff tells us we need to delete a line. Here, the output is telling us "After line 2 in the first file, a line needs to be added: line 3 from the second file." It then shows us what that line is. > Oh yeah, I also need to buy grated cheese. Oh yeah, I also need to buy grated cheese. The three dashes (" -") merely separate the lines of file 1 and file 2. Lines preceded by a are lines from the second file.In our output above, " 2,4c2,4" means: "Lines 2 through 4 in the first file need to be changed to match lines 2 through 4 in the second file." It then tells us what those lines are in each file: line numbers corresponding to the second file.a letter ( a for add, c for change, or d for delete), and.line numbers corresponding to the first file,.The first line of the diff output contains: The important thing to remember is that when diff is describing these differences to you, it's doing so in a prescriptive context: it's telling you how to change the first file to make it match the second file. Let's take a look at what this output means. then we can use diff to automatically display for us which lines differ between the two files with this command: diff file1.txt file2.txt and file2.txt contains these four lines: I need to buy apples. If file1.txt contains the following four lines of text: I need to buy apples. However, it can optionally generate a script (if the -e option is specified) for the program ed or ex which can apply the changes.įor example, consider two files, file1.txt and file2.txt. The diff software does not actually change the files it compares. Using diff to create an editing script.Finding differences in directory contents.
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