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 input/output 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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