Issue
I've come to know the global (/g
) flag to mean the action should take place globally in a file.
If I want to replace all instances of "hello world" with "goodbye space", I would add /g
on the end of the statement.
That makes sense. However...
I was writing a sed
replace command and noticed that even if I didn't include /g
it would still replace all instances in a file. Below is the contents of my .txt
file:
hello there
how is life
today is over
today is over
don't be sad
today is over
tomorrow is a new day
Now, I want to file all of these "today is over" lines and replace them with "tomorrow will begin". Therefore, I wrote the below code:
YOUR_FILE='testing.txt'
LINE="today is over"
sed -i "" "s/$LINE/tomorrow will begin/" $YOUR_FILE
Despite NOT including the global flag at the end, it still replaces all instances of today is over
with tomorrow will begin
.
Can someone explain this behavior to me as I haven't been able to find anything about it. Why does it replace all instances even when I omit the /g
part at the end?
Alternatively, if I wanted to only remove the first instance, how would I go about specifying that?
I am doing this on a Mac.
Solution
The global flag allows sed to replace multiple matches in the same line.
$ echo 'world world' > somefile
$ sed 's/world/hello/' somefile
hello world
$ sed 's/world/hello/g' somefile
hello hello
Answered By - jirassimok Answer Checked By - Timothy Miller (WPSolving Admin)