Calling Bash Commands With Multiple args From Ruby?

Question

I write this code in my rails project.It's to execute a shell script ,But my shell script can catch @directdown only.

rails script

@cmd = "/downafile.sh #{@directdown} #{@file.id} #{@filename}"
`#{@cmd}`

shell script

echo $1 >> /tmp/ceshi.tmp
echo $2 >> /tmp/ceshi.tmp
echo $3 >> /tmp/ceshi.tmp

Thanks.

Ashish · Accepted Answer · 2011-03-03 11:40:38Z

1

`` and system command works in similar manner. But system method will return true on success.

Try with this:

@cmd = "/downafile.sh '#{@directdown}' '#{@file.id}' '#{@filename}'"
  `#{@cmd}`

answered Mar 3, 2011 at 11:40

Ashish

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1 Comment

Charles Duffy Over a year ago

This is not safe -- consider the case where a filename is passed of $(rm -rf ~)'$(rm -rf ~)' (and yes, literal quotes are allowed in UNIX filenames).

rubyprince · Accepted Answer · 2011-03-03 11:50:15Z

1

Try using puts @cmd to see the command generated and see whether the command is what you intended. If it is try executing it from the terminal to test whether your shell script works. I think the parameters @file.id and @filename value may be nil so on interpolation it will be replaced by "". puts their values also to check.

answered Mar 3, 2011 at 11:50

rubyprince

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5 Comments

yiqun Over a year ago

hi,i can see whole args when i puts @cmd

rubyprince Over a year ago

@jean...try using that in the terminal..and see what happens?

yiqun Over a year ago

it's solved.@cmd = "/downafile.sh '#{@directdown}' '#{@file.id}' '#{@filename}'"

rubyprince Over a year ago

@jean..it may be because the varible values may have spaces in between and part after space will be treated as another argument..so using '' in arguements will force it to take it correctly

Charles Duffy Over a year ago

@jean, that's not a safe solution against hostile names. A filename that contains a literal quote character could escape the quoting and run arbitrary shell commands.

Jesús Sánchez · Accepted Answer · 2011-03-03 11:20:56Z

-1

I don't know what is the meaning of `` in Ruby, but I think you can use the system function to invoke an external program. Something like,

   @cmd = "/downafile.sh #{@directdown} #{@file.id} #{@filename}"
   system(@cmd)

Hope it helps.

answered Mar 3, 2011 at 11:20

Jesús Sánchez

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3 Comments

rubyprince Over a year ago

system(@cmd) executes the command and gives true if the command was executed successfully and otherwise false. `` executes the command and returns its screen output. For example ` ls ` will give "app\nconfig\ndb\ndoc\nlib\nlog\npublic\nRakefile\nREADME\nscript\ntest\ntmp\nvendor\n" as output.

yiqun Over a year ago

6 Ways to Run Shell Commands in Ruby

Charles Duffy Over a year ago

system() use permits shell injection attacks -- consider a file named $(rm -rf ~)'$(rm -rf ~)'.txt (yes, all those characters are allowed in filenames on Linux).

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