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bashhttp-redirecttreestderrls

Bash stderr redirection doesnt work in some cases

I have two cases to share where I didn't find the stderr redirection (2>) working as expected:

In both the cases the file/directory, on which the operations are being performed, don't exist.

Case 1:

When you give 2 commands in pipe:

[root@example ~]# cat test2.txt | grep -i 'third'
cat: test2.txt: No such file or directory

[root@example ~]# cat test2.txt | grep -i 'third' 2> /dev/null
cat: test2.txt: No such file or directory

But redirection works simply with grep alone as a command:

[root@example ~]# grep -i 'third' test2.txt 
grep: test2.txt: No such file or directory

[root@example ~]# grep -i 'third' test2.txt 2> /dev/null
<redirection worked properly>

I know that using cat and then grep doesn't make sense but I am just being curious here.

Case 2:

When you use the tree command:

[root@example ~]# tree /var/crash2
/var/crash2 [error opening dir]

0 directories, 0 files

[root@example ~]# tree /var/crash2 2> /dev/null
/var/crash2 [error opening dir]

0 directories, 0 files

But this isn't the case with ls command:

[root@example ~]# ls -ld /var/crash2
ls: cannot access /var/crash2: No such file or directory

[root@example ~]# ls -ld /var/crash2 2> /dev/null
<redirection worked properly>

Where's the problem here?

Solution

    1. cat having an error not grep as mentioned by Cyrus

    2. tree command shows "error opening dir" in standard output

    So the command shows if we use 2>/dev/null

    root@ubuntu:~# tree -if test 2>/dev/null
test [error opening dir]

0 directories, 0 files

    The same thing you mentioned was reported as a bug before, refer: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=76594