generate blank files

Question

I want to empty 3 files or generate them if they do not exist. Is the following command correct?

> myone.txt > mytwo.txt > mythree.txt

or is there any better way?

Answer 1

No, not from the shell. Reading the generated system calls for this, it's also pretty efficient for a shell builtin:

matt@stanley:~$ strace bash -c '> a > b > c'
...
open("a", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3
fcntl64(1, F_GETFD)                     = 0
fcntl64(1, F_DUPFD, 10)                 = 10
fcntl64(1, F_GETFD)                     = 0
fcntl64(10, F_SETFD, FD_CLOEXEC)        = 0
dup2(3, 1)                              = 1
close(3)                                = 0
open("b", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3
fcntl64(1, F_GETFD)                     = 0
fcntl64(1, F_DUPFD, 10)                 = 11
fcntl64(1, F_GETFD)                     = 0
fcntl64(11, F_SETFD, FD_CLOEXEC)        = 0
dup2(3, 1)                              = 1
close(3)                                = 0
open("c", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3
fcntl64(1, F_GETFD)                     = 0
fcntl64(1, F_DUPFD, 10)                 = 12
fcntl64(1, F_GETFD)                     = 0
fcntl64(12, F_SETFD, FD_CLOEXEC)        = 0
dup2(3, 1)                              = 1
close(3)

Answer 2

I usually use touch to create empty files. It is usually cast as a utility to update timestamps, but also will create the named file if it does not exist.

Answer 3

you can use touch to create empty files if there haven't existed. Otherwise, what you are doing is all right

>file1 >file2 

Answer 4

Alternative to touch is using dd which can be used to truncate existing files,

dd if=/dev/null of=moo count=0

Answer 5

One thing that you can't do with > is something like >file{0..9} or >file{foo,bar,baz}. However, if your system has truncate you can do this:

truncate --size 0 file{0..9}
truncate --size 0 file{foo,bar,baz}

By using different arguments with --size you can shrink or extend a file, but it doesn't empty it first unless you use 0 for the size (in the first of two passes, for example). Extended files are padded with nulls.