PHP shell_exec(), exec(), and system() returning only partial output

Question

I am trying to use a PHP script to run the siege command and capture the output.

Running the following in the shell provides these results:

$ /usr/local/bin/siege -c30 -t30s -f urls.txt

.....
HTTP/1.1 200   0.10 secs:   11246 bytes ==> GET  /*******.html
HTTP/1.1 200   0.11 secs:   11169 bytes ==> GET  /*******.html
HTTP/1.1 200   0.10 secs:   11246 bytes ==> GET  /*******.html

Lifting the server siege..      done.

Transactions:               1479 hits
Availability:             100.00 %
Elapsed time:              29.05 secs
Data transferred:          14.69 MB
Response time:              0.10 secs
Transaction rate:          50.91 trans/sec
Throughput:             0.51 MB/sec
Concurrency:                5.33
Successful transactions:        1479
Failed transactions:               0
Longest transaction:            0.16
Shortest transaction:           0.09

When running the same command in PHP via exec(), shell_exec(), system(), I only receive the following output.

HTTP/1.1 200   0.10 secs:   11246 bytes ==> GET  /*******.html
HTTP/1.1 200   0.11 secs:   11169 bytes ==> GET  /*******.html
HTTP/1.1 200   0.10 secs:   11246 bytes ==> GET  /*******.html

Since I'm really only interested in the results provided by siege, this data is useless to me. For some reason its ignoring the results of the siege.

Here's an example of what I'm doing in PHP...

exec('/usr/local/bin/siege -c30 -t30s -f urls.txt', $output);

Answer 1

The siege program writes its output to two different standard streams: stdout and stderr. PHP's exec() only captures stdout. To capture both, you need to redirect (using your shell) stderr to stdout so that everything is in the one stream that PHP captures.

To do this, add 2>&1 at the very end of your command. In your example, that would be:

exec('/usr/local/bin/siege -c30 -t30s -f urls.txt 2>&1', $output);

(I have installed siege and verified that it uses both stdout and stderr and that the output redirection works.)