Use multiline PHP variable as argument for executing bash script

Question

In PHP, I have a variable that returns a multi-line text, similar to what is displayed below.

*
*clefF4
*k[f#c#g#d#a#]
*d:
*M6/4

I then want to use this variable in PHP as an argument to execute a bash script. My PHP code for doing so is below (Where $filechosen is the string of text above):

$output = shell_exec("/path/to/bash/script.sh $filechosen");
echo "<pre>$output</pre>";

Below is that extremely simple bash script that uses the variable '$filechosen' as an argument:

#!/bin/bash

returnExpression=$(echo "$1" | grep 'k\[')
echo $returnExpression

However, when I run this, I get no output. Why is this?

Barmar · Accepted Answer · 2019-03-18 01:37:14Z

2

You should always escape variables that you're substituting into command lines, and PHP provides a function escapeshellarg() to do it.

$output = shell_exec("/path/to/bash/script.sh " . escapeshellarg($filechosen));

or

$escaped = escapeshellarg($filechosen);
$output = shell_exec("/path/to/bash/script.sh $escaped");

edited Mar 18, 2019 at 1:37

answered Mar 18, 2019 at 1:13

Barmar

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8 Comments

user10855478 Over a year ago

With slight modification, this worked! Thank you very much.

Barmar Over a year ago

What was the modification?

user10855478 Over a year ago

For some reason, the syntax in the answer wasn't working, so I set a separate variable, filechoose: $filechose = escapeshellarg($filechosen); Then the execution of the script was changed to this: $output = shell_exec("/path/to/bash/script.sh $filechose");

Barmar Over a year ago

There really shouldn't be any difference between concatenating variables and substituting into the string. Did you remember to leave a space after .sh when you concatenated?

user10855478 Over a year ago

I did. For some reason, it still isn't working with concatenation.

|

Pinke Helga · Accepted Answer · 2019-03-20 12:51:55Z

In GNU/Linux the common way of commands is to process streams. Also grep does so. Whenever possible, you should not break this pattern. In your paricular example it does not make sense to wrap it into positional parameters.

You can use popen to write a stream to the executed command:

<pre>
<?php

$filechosen = <<<_EOS_
*
*clefF4
*k[f#c#g#d#a#]
*d:
*M6/4
_EOS_;


if($handle = popen("grep 'k\\['", "w"))
{
  fwrite($handle, $filechosen);
  pclose($handle);
}

?>
<pre>

Use proc_open function instead when you want to read the output stream into a variable.

if($handle = proc_open("grep 'k\\['", [['pipe', 'r'], ['pipe', 'w'], ['pipe', 'w']], $streams))
{
  [$stdin, $stdout, $stderr] = $streams;

  fwrite($stdin, $filechosen);
  fclose($stdin);

  $output = stream_get_contents($stdout);
  fclose($stdout);

  $error  = stream_get_contents($stderr);
  fclose($stderr);

  proc_close($handle);
  echo $output;
}

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