Ruby check if mounted inside an if condition

Question

contents of a.rb is :

if system("mount | grep /boot") != ""
  print "true"  # or do something
else 
  print "false" # or do something else 
end

Running this code doesn't print "true" or "false", but prints the output of system call.

]$ ruby a.rb 
/dev/sda1 on /boot type ext4 (rw)

What's the right syntax to check the if condition ?

score 6 · Answer 1 · answered Apr 22 '14 at 20:22

6

if `mount | grep /boot` != ""
  print "true"  # or do something
else 
  print "false" # or do something else 
end

answered Apr 22 '14 at 20:22

fl00r

82,987
33
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1

can you explain what's happening with the `system(...)` – iamauser Apr 22 '14 at 20:25
1

`system` call returns true if command was found and run successfully – fl00r Apr 22 '14 at 20:28
1

Here is a good explanation http://stackoverflow.com/questions/6338908/ruby-difference-between-exec-system-and-x-or-backticks – fl00r Apr 22 '14 at 20:28
Note that those are backticks around the system command, not single quotes. – Ecnalyr Apr 22 '14 at 20:33

score 1 · Answer 2 · answered Jun 29 '15 at 23:43

1

In ruby, backticks cause the process to fork, which is expensive and slow. Instead, you could read /etc/mtab and look at the content which prevents forking.

if File.read('/etc/mtab').lines.grep(/boot/)[0]
  # not nil, its mounted
else
  # its nil, not mounted
end

answered Jun 29 '15 at 23:43

Tom

412
2
9

Hi, can you tell me what the 0 represents in the array index? – Vigneshwaran Aug 06 '15 at 13:16
1

See the ruby docs for Array#grep. When you grep an array, you get an array back. We're using grep to search the array (of lines from /etc/mtab) for "boot". If its found, it'll exist in the first element. – Tom Jul 04 '17 at 23:50

score 1 · Answer 3 · edited May 19 '17 at 17:48

1

Don't use system calls, instead you can try this (fromFile path depends of your operating system, in RedHat is /proc/mounts):

fromFile='/proc/mounts'
toFind='/boot'
if File.readlines(fromFile).grep(toFind).size > 0
    print "true"  # or do something
else
    print "false" # or do something else 
end

edited May 19 '17 at 17:48

Nacimota

22,395
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answered May 19 '17 at 17:29

Marc

11
1

Ruby check if mounted inside an if condition

3 Answers3