Name
eval
Synopsis
eval
args
Typically, eval is used in shell scripts, and
args
is a line of code that may contain
shell variables. eval forces variable expansion to happen first and
then runs the resulting command. This “double
scanning” is useful any time shell variables contain
I/O redirection symbols, aliases, or other shell variables. (For
example, redirection normally happens before variable expansion, so a
variable containing redirection symbols must be expanded first using
eval; otherwise, the redirection symbols remain uninterpreted.)
Examples
The following line can be placed in the .login file to set up terminal characteristics:
set noglob eval `tset -s xterm` unset noglob
The following commands show the effect of eval
:
%set b='$a'
%set a=hello
%echo $b
Read the command line once $a %eval echo $b
Read the command line twice hello
Another example of eval
can be found under
alias
.
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