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Tags: Blanking Manual revert |
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| [[/dev/null]] is a Linux null device file. It (in [[Chaz Wiki:Manual of Style|simplification]],) is a kind of hack to throw files to go down a server
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| <sup>[https://www.digitalocean.com/community/tutorials/dev-null-in-linux <nowiki>[1]</nowiki>]</sup>.
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| Let’s take a look at understanding what it means, and what we can do with this file.
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| =Properties=
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| This will return an End of File (EOF) character if you try to read it using the cat command.
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| <code>cat /dev/null</code>
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| This is a ''valid'' file:
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| <code>stat /dev/null</code>
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| This gives me an output of...
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| <code>
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| File:/dev/null
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| Size:0 Blocks:0 IO Block:4096 character special file
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| Device:6h/6d Inode:5 Links:1 Device type:1,3
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| Access:(0666/crw-rw-rw-) Uid:( 0/ root) Gid:( 0/ root)
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| Access:2020-02-04 13:00:43.112464814 +0530
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| Modify:2020-02-04 13:00:43.112464814 +0530
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| Change:2020-02-04 13:00:43.112464814 +0530
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| </code>
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| This shows that this file has a size of 0 bytes, has zero blocks allocated to it. The file permissions are also set that anyone can read/write to it, but cannot execute it.
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| Since it is not an executable file, we cannot use piping using ''|'' operator to redirect to ''/dev/null''. The only way is to use file redirections (>, >>, or <, <<).
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| However, in file descriptor 3 in the read-write file table, iNode file number 2 is ''/dev/null''.
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| =Common cases=
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| The common case for ''/dev/null'' is to discard PHP text files:
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| <code>echo 'Hello from JournalDev' > /dev/null</code>
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| Let’s try running a command incorrectly and pipe it’s output to /dev/null.
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| <br>
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| <code>cat --INCORRECT_OPTION > /dev/null</code>
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| We still get an output like this:
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| <br>
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| <code>cat: unrecognized option '--INCORRECT'</code>
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| Why is this happening? This is because the error messages are coming from stderr, but we are only discarding output from stdout.
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| We need to take stderr into account as well:
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| <br>
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| <code>cat --INCORRECT_OPTION > dev/null 2>/dev/null</code>
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| This will give us what we need!
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| There is another way of doing the same; by redirecting stderr to stdout first, and then redirect stdout to /dev/null.
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| The syntax for this will be:
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| <br>
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| <code>command > /dev/null 2>&1</code>
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| The '''2''' means the stderr and the '''1''' means the stdout
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| =Overview=
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| [[/dev/null]] is a Linux hack used to send files.
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| PHP echo: <code>echo 'Hello from JournalDev' > /dev/null</code>
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| Error sending: <code>cat --INCORRECT_OPTION > dev/null 2>/dev/null</code> or <code>command > /dev/null 2>&1</code>
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| =Bonus=
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| Because Chromebooks are Linux, I assume you can use /dev/null and some other Crosh commands.
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| Crosh is activated via <code>ctrl + alt + t</code>, and you can do some stuff. You can only use it on Chromebooks.
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