eval command

Synopsis

/eval <command-text>
/eval {<commands>}

Description

eval treats its arguments as EPIC script syntax and executes them. Its most common use is at the input prompt: ordinary interactive commands do not expand $ variables, but eval runs its argument text through the script parser so expandos are substituted.

Inside a script, command statements are normally expanded before their handler runs. eval then parses and expands the resulting text again. This extra pass can resolve an indirect variable reference, but it also lets text become new command syntax.

For example, in a script:

if (1) {
    @ variable = 'this is some text';
    @ indirect = '$variable';
    echo $indirect;
    eval echo $indirect;
}

The two echo commands display:

$variable
this is some text

The first pass replaces $indirect with the literal text $variable. The ordinary echo handler prints that text. In eval echo $indirect, eval receives echo $variable, and its execution pass substitutes the variable's value before running echo.

Parsing and scope

There are no options or required arguments beyond the text you want to execute. With no text, it does nothing. It accepts command statements, semicolon-separated blocks, and expression statements such as @ foo = 4 + 5; it does not return the expression result as a function value. Any output and effects come from the executed statements.

Braces protect their contents from the outer command-expansion pass. For example, eval { echo $foo } evaluates the braced command when that block runs, instead of substituting $foo while preparing the eval statement. Exact expansion depends on the text's braces and escapes; eval is not an unlimited recursive substitution operation.

Execution uses the current server, window/output context, and local-variable scope. It does not create an alias scope, change the current conversation target, or send unprefixed command text as chat. Saved positional arguments such as $* are the current caller's arguments, or empty when invoked without a script argument context.

Normal parser errors and control flow apply. A valid return, break, or continue can stop evaluation and propagate to its surrounding call or loop. Braces, parentheses, and command names must obey ordinary script syntax; eval does not prevalidate the whole block or undo earlier statements if a later one fails.

The command is available in every build and needs no IRC connection unless the executed text does.

Using input safely

Do not pass text from a server or another user to eval merely to display it. Semicolons and other syntax in that text can become commands on the additional parsing pass. Use echo directly for display.

For example, eval echo $message can execute a second command if the expanded message contains hello; echo another command. Bracing the original expression is not a general sanitizer for arbitrary text later incorporated into evaluated code.

Example at the input prompt

To expand the nickname expando:

/eval echo My nickname is $N

Source

See source/commands.c for evalcmd(), runcmds(), parse_block(), and parse_statement(). source/expr.c implements statement boundaries and expansion, including brace protection.