For reasons I am completely unwilling to research, just doing `> filename` has not worked for me in a while.
Since then I memorized this: `cat /dev/null >! filename`, and it has worked on systems with zsh and bash.
Since then I memorized this: `cat /dev/null >! filename`, and it has worked on systems with zsh and bash.
However, it won't work in bash. It will create file named "!" with the same contents as "filename". It is equivalent to "cat /dev/null filename > !". (Bash lets you put the redirection almost anywhere, including between one argument and another.)
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[1] See https://zsh.sourceforge.io/Doc/Release/Redirection.html
In that case I'll just always use `truncate -s0` then. Safest option to remember without having to carry around context about which shell is running the script, it seems.
I believe "> filename" only works correctly if you're root (at least in my experience, if I remember correctly).
EDIT: To remove <> from filename placeholder which might be confusing, and to put commands in quotes.
It saved me just yesterday when I needed to truncate hundreds of gigabytes of Docker logs on a system that had been having some issues for a while but I didn't want to recreate containers.
"truncate -s 0 /var/lib/docker/containers/**/*-json.log"
Will truncate all of the json logs for all of the containers on the host to 0 bytes.
Of course the system should have had logging configured better (rotation, limits, remote log) in the first place, but it isn't my system.
EDIT: Missing double-star.*
openat(AT_FDCWD, "file", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
O_TRUNC
If the file already exists and is a regular file and the
access mode allows writing (i.e., is O_RDWR or O_WRONLY) it
will be truncated to length 0.
... MULTIOS=1 > file