Question

I am updating a C shell script that uses a sed command:

sed '/EOF/r $thingToAdd' $fileToAddItTo > $newFileOutput

I can’t seem to find what the /r command means or does. I think it is for a find and replace (similar to /s..../g).

Any ideas?

Answer 1

r is used to read a file and append it at the current point.

The point in your example is the address /EOF/ which means this script will find the line containing EOF and then append the file specified by $thingToAdd after that point. Then it will process the rest of the file.

In other words:

$fileToAddItTo  +  $thingToAdd  =  $newFileOutput
--------------     -----------     --------------
1                  5               1
2                  6               2
3                                  3
EOF                                EOF
4                                  5
                                   6
                                   4

You can see this in action in the following transcript:

pax$ cat file1 ; echo === ; cat file2
file1_line:1
file1_line:2
file1_line:3
file1_line:4 EOF
file1_line:5
===
file2_line:1
file2_line:2

pax$ sed '/EOF/r file2' file1
file1_line:1
file1_line:2
file1_line:3
file1_line:4 EOF
file2_line:1
file2_line:2
file1_line:5

---

And, in response to the question in your comment about whether it will do this for every line containing the EOF string, yes it will:

pax$ cat file1 ; echo === ; cat file2
file1_line:1
file1_line:2 EOF
file1_line:3
file1_line:4 EOF
file1_line:5
===
file2_line:1
file2_line:2

pax$ sed '/EOF/r file2' file1
file1_line:1
file1_line:2 EOF
file2_line:1
file2_line:2
file1_line:3
file1_line:4 EOF
file2_line:1
file2_line:2
file1_line:5

And, it will do it for every line containing the EOF string. Normally you would restrict something like this to lines containing only the EOF string since that’s usually how it’s set up (with the EOF being the only contents of that line). You could do that simply by changing the address to /^EOF$/ (the ^ and $ are the start-of-line and end-of-line anchors respectively).

Otherwise it would pick up lines you might not expect, like those containing HEREOF, WRITEOFF or NEOFACISM.