Can files be created with permissions set on the command line?

When creating directories, mkdir -m <mode> <dir> provides for creating one or more directories with the given mode/permissions set (atomically).

Is there an equivalent for creating files, on the command line?

Something akin to:

open("file", O_WRONLY | O_APPEND | O_CREAT, 0777);

Is using touch followed by a chmod my only option here?

Edit: After trying out teppic’s suggestion to use install, I ran it through strace to see how close to atomic it was. The answer is, not very:

$ strace install -m 777 /dev/null newfile
...
open("newfile", O_WRONLY|O_CREAT|O_EXCL, 0666) = 4
fstat(4, {st_mode=S_IFREG|0666, st_size=0, ...}) = 0
...
fchmod(4, 0600)                         = 0
close(4)                                = 0
...
chmod("newfile", 0777)                  = 0
...

Still, it’s a single shell command and one I didn’t know before.

Answers:

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Method 1

You could use the install command (part of GNU coreutils) with a dummy file, e.g.

install -b -m 755 /dev/null newfile

The -b option backs up newfile if it already exists. You can use this command to set the owner as well.

Method 2

touch always creates the file if it doesn’t exist, always follows symbolic links, and always makes the file non-executable. You can decide the read and write bits through the umask.

(umask 077; touch file)  # creates a 600 (rw-------) file
(umask 002; touch file)  # creates a 664 (rw-rw-r--) file

“Safe” atomic file creation (in particular, with O_NOFOLLOW) is not possible with traditional shell tools. You can use sysopen in perl. If you have the BSD-inspired mktemp utility, it creates a file atomically with O_NOFOLLOW; you’ll have to to call chmod afterwards if the default mode of 600 is not the right one.

Method 3

Building on @teppic’s answer, if you want to create the file with content and mode at the same time (bash):

install -m 755 <(echo commands go here) newscript

<() places the output into a temporary file, see Process-Substitution

Method 4

I have a bash script in my home directory /home/anthony/touchmod.sh containing:

#!/bin/bash

touch "$2"
chmod "$1" "$2"

So if I need to create readme.txt with 644 permissions I can type:

~/touchmod.sh 644 readme.txt

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0