CODEWITHSUNDEEP
linuxbashshell
Abhishek Gupta
Abhishek Gupta

Reputation: 4166

Difference b/w ls -la and ls -la > ls-1.txt

If I do ls -la, I get results like

total 16
drwxr-xr-x   4 rockse  staff  136 Apr 28 16:55 .
drwx------+ 23 rockse  staff  782 Apr 28 16:48 ..
-rw-r--r--   1 rockse  staff   32 Apr 28 16:49 1.sh
-rw-r--r--   1 rockse  staff  215 Apr 28 17:01 ls-1.txt

But if I do ls -la > ls-1.txt, I get this

total 8
drwxr-xr-x   4 rockse  staff  136 Apr 28 16:55 .
drwx------+ 23 rockse  staff  782 Apr 28 16:48 ..
-rw-r--r--   1 rockse  staff   32 Apr 28 16:49 1.sh
-rw-r--r--   1 rockse  staff    0 Apr 28 17:06 ls-1.txt

I understand that a file is created and then ls -la is written to the same but why doesn't it capture the snapshot of ls -la before creating the file because we are just writing stdout to a file ?

Upvotes: 0

Views: 784

Answers (1)

Barmar
Barmar

Reputation: 781726

The redirection is done by the shell, not the program you're running. The processing done by the shell to implement this is similar to this (simplified):

  1. Fork a child process
  2. Open the output file
  3. Connect stdout to the output file stream
  4. Execute the program

Step 2 creates the file, so it will be visible when the program runs in step 4.

If step 2 were done after step 4, it wouldn't be possible to change the program's stdout to point to it.

Upvotes: 1

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