man eval () - construct command by concatenating arguments
eval - construct command by concatenating arguments
eval [argument ...]
The eval utility shall construct a command by concatenating arguments together, separating each with a <space>. The constructed command shall be read and executed by the shell.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
If there are no arguments, or only null arguments, eval shall return a zero exit status; otherwise, it shall return the exit status of the command defined by the string of concatenated arguments separated by <space>s.
CONSEQUENCES OF ERRORS
The following sections are informative.
foo=10 x=foo y='$'$x echo $y $fooeval y='$'$x echo $y 10
Special Built-In Utilities
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .