Program execution Functions
Take care if using escapeshellarg() on serialized objects. Serialized objects contain null bytes, and escapeshellarg stops on the first null byte so you will not receive the full argument. (I consider this a bug, though not sure what it should do in this case. Probably serialize shouldn't have used null bytes, but too late for that now).
The workaround I've found to pass serialized objects on the command line is to base64_encode() them first and decode on the other side.
escapeshellarg
(PHP 4 >= 4.0.3, PHP 5)
escapeshellarg — Escape a string to be used as a shell argument
Description
string escapeshellarg
( string
$arg
)escapeshellarg() adds single quotes around a string and quotes/escapes any existing single quotes allowing you to pass a string directly to a shell function and having it be treated as a single safe argument. This function should be used to escape individual arguments to shell functions coming from user input. The shell functions include exec(), system() and the backtick operator.
Parameters
-
arg -
The argument that will be escaped.
Return Values
The escaped string.
Examples
Example #1 escapeshellarg() example
<?php
system('ls '.escapeshellarg($dir));
?>
See Also
- escapeshellcmd() - Escape shell metacharacters
- exec() - Execute an external program
- popen() - Opens process file pointer
- system() - Execute an external program and display the output
- backtick operator
add a note
User Contributed Notes
escapeshellarg - [18 notes]
sblyons+php at gmail dot com ¶
9 months ago
phil at philfreo dot com ¶
2 years ago
When escapeshellarg() was stripping my non-ASCII characters from a UTF-8 string, adding the following fixed the problem:
<?php
setlocale(LC_CTYPE, "en_US.UTF-8");
?>
vosechu at roman-fleuve dot com ¶
9 years ago
If escapeshellarg() returned something on a null input it would probably break more programs than it helps. Even if it's two "'s or two ''s, this function wouldn't work the way it's supposed to (that is, returning nothing).
However, most people do not put "" into their commands but I can see where it might be useful at the same time.
Perhaps an option in the command that would return the type of null we want. I might want the null character to be returned, someone else might want '', and someone else might want nothing at all.
php at floris dot nu ¶
10 years ago
i also thought the output was gonna be between 's because that's the way windows handles arguments with spaces in them. i think we have a unix <> windows misunderstanding here...
Audun ¶
4 years ago
The reason why % are replaced with space on windows is that it is impossible in cmd.exe to escape or quote them so that environment variables are not expanded. If for instance %path% is in your argument it will always be expanded, so the only safe thing to do is to replace % with something else.
Alternatively, you could wipe the environment before making the call to exec(), but that has its side-effects.
phpman at crustynet dot org dot uk ¶
3 years ago
The comment from 'rmays at castlecomm dot com' is incorrect: single quotes cannot be backslash-escaped inside a single-quoted string when constructing a shell argument. The output from this function is in fact correct. It drops out of the single-quoted string, includes a literal single quote with a backslash-escape, then resumes the single-quoted string. Observe:
[shellarg.php]
<?php
system("echo ' single quote\'d '");
system("echo ' single quote'\''d '");
?>
$ php shellarg.php
sh: -c: line 0: unexpected EOF while looking for matching `''
sh: -c: line 1: syntax error: unexpected end of file
single quote'd
phpnet at lostreality dot org ¶
7 years ago
This function does not escape $ it seems. This lets user embed shell variables such as $PATH into commands, which you may or may not want to allow. I'm using shell_exec() because I need the entire command as one string, and need access to the stdout data as one string as well.
Anonymous ¶
7 years ago
According to my test (PHP 4.3.10) there is no need to call escapeshellarg() on a filename that is being written to by proc_open, and probably others. E.g.
<?php
$process = proc_open("echo hi",
array(
0 => array("pipe", "r"),
1 => array("file", 'filename with spaces', "w"),
2 => array("pipe", "w"),
),
$pipes);
?>
creates a file named:
filename with spaces
In fact,
<?php
1 => array("file", escapeshellarg('filename with spaces')
?>
creates a file named:
'filename with spaces'
(quotes included in filename.) Maybe all the PHP functions that take a filename as a separate parameter work this way. I guess you just need to escape filenames when they are part of a single string command line such as with the backtick operator, system(), etc.
wijnand at jpresult dot nl ¶
20 days ago
Here's a quick and dirty replacement of this function in case you need to deal with special characters.
<?php
/**
* An ugly, non-ASCII-character safe replacement of escapeshellarg().
*/
function escapeshellarg_special($file) {
return "'" . str_replace("'", "'\"'\"'", $file) . "'";
}
?>
jrbeaure at uvm dot edu ¶
3 years ago
When running a string of LaTeX code containing hyphens through as an argument to pdflatex escaped using this command, it will result in failure.
info at infosoporte dot com ¶
4 years ago
If escapeshellarg() function removes your accents (like รก, a with an 'accute') from the given string, ensure your LC_ALL variable is correct. If using it via web, you need to restart Apache or the corresponding web server after setting LC_ALL with a export LC_ALL=es_ES.utf8 (for example) from your shell.
Cameron ¶
4 years ago
in regards to the bug returning no string where it should return "" or '', just do
<?php
shell_exec("example ". (($arg=escapeshellarg($arg))? $arg : "''"));
?>
egorinsk at gmail dot com ¶
6 years ago
Under Windows, this function puts string into double-quotes, not single, and replaces %(percent sign) with a space, that's why it's impossible to pass a filename with percents in its name through this function.
php at atu dot cjb dot net ¶
6 years ago
In reply to vosechu at roman-fleuve dot com: Even if it's two "'s or two ''s, this function wouldn't work the way it's supposed to (that is, returning nothing). However, most people do not put "" into their commands...
When many commands are executed, the order of the parameters is of critical importance, especially with shell scripts where $1, $2, $3, etc. are commonly used without checking what is stored in them first. In such cases, having this function not return even an empty parameter will break things.
As was mentioned earlier, putting two single quotes '' before the output of this function will remedy this issue, as the '' in itself will not add any characters to that command line parameter, but it will turn it into a placeholder for that parameter when the value is empty.
Anonymous ¶
6 years ago
Most of the comments above have misunderstood this function. It does not need to escape characters such as '$' and '`' - it uses the fact that the shell does not treat any characters as special inside single quotes (except the single quote character itself). The correct way to use this function is to call it on a variable that is intended to be passed to a command-line program as a single argument to that program - you do not call it on command-line as a whole.
The person above who comments that this function behaves badly if given the empty string as input is correct - this is a bug. It should indeed return two single quotes in this case.
antony lesuisse ¶
9 years ago
NOTE: If you are using PHP >= 4.2 you should use the pcntl_* (Process
Control) functions instead of this hack.
PHP, before version 4.2, didn't provide any execl(3)-like or
execv(3)-like methods to invoke external programs, thus everything
goes trough /bin/sh -c and we are forced to quote arguments.
To make it worse escapeshellarg() behaves badly (IMHO) with an empty
string:
<?php
echo "mime-construct --to ".escapeshellarg($to)." --cc a@a.com";
?>
The following function is a wrapper to system(), and it can be adapted
to popen(),exec(),shell_exec():
<?php
# system with perl? semantics
function lib_system() {
$arg=func_get_args();
if(is_array($arg[0]))
$arg=$arg[0];
$cmd=array_shift($arg);
foreach($arg as $i) {
$cmd.=" ''".escapeshellarg($i);;
}
system($cmd);
}
# example1
lib_system("mime-construct","--output", "--to",$a,"--string",$b);
# example2
lib_system(array("mime-construct","--output", "--to",$a,"--string",$b));
?>
rmays at castlecomm dot com ¶
3 years ago
A warning on how this handles single quotes in a string
Example:
print escapeshellarg(" single quote'd ");
Expected:
' single quote\'d '
Actual Result:
' single quote'\''d '
So if you pass a ' into this function, it will return an incorrectly escaped string!!!!
ludvig dot ericson at gmail dot com ¶
7 years ago
It seems from my tests that escapeshellarg("`ls -al`") is _NOT_ escaped into \`ls -al\` as it should be.
Anyway, a bash/sh environment does not seem to interprett ` inside of a singleqoute (').
$ echo "`echo hello`"
hello
$ echo '`echo hello`'
`echo hello`
$ echo "\`echo hello\`"
`echo hello`
Just a tip.