PHP shell_exec() vs exec()

Here are the differences. Note the newlines at the end.

> shell_exec('date')
string(29) "Wed Mar  6 14:18:08 PST 2013\n"
> exec('date')
string(28) "Wed Mar  6 14:18:12 PST 2013"

> shell_exec('whoami')
string(9) "mark\n"
> exec('whoami')
string(8) "mark"

> shell_exec('ifconfig')
string(1244) "eth0      Link encap:Ethernet  HWaddr 10:bf:44:44:22:33  \n          inet addr:192.168.0.90  Bcast:192.168.0.255  Mask:255.255.255.0\n          inet6 addr: fe80::12bf:ffff:eeee:2222/64 Scope:Link\n          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1\n          RX packets:16264200 errors:0 dropped:1 overruns:0 frame:0\n          TX packets:7205647 errors:0 dropped:0 overruns:0 carrier:0\n          collisions:0 txqueuelen:1000 \n          RX bytes:13151177627 (13.1 GB)  TX bytes:2779457335 (2.7 GB)\n"...
> exec('ifconfig')
string(0) ""

Note that use of the backtick operator is identical to shell_exec().

Update: I really should explain that last one. Looking at this answer years later even I don't know why that came out blank! Daniel explains it above -- it's because exec only returns the last line, and ifconfig's last line happens to be blank.

shell_exec returns all of the output stream as a string. exec returns the last line of the output by default, but can provide all output as an array specifed as the second parameter.

See

• http://php.net/manual/en/function.shell-exec.php
• http://php.net/manual/en/function.exec.php

shell_exec - Execute command via shell and return the complete output as a string

exec - Execute an external program.

The difference is that with shell_exec you get output as a return value.