CODEWITHSUNDEEP
expect
chromechris
chromechris

Reputation: 214

What does "-r" mean as in the Expect's "expect -r PATTERN" command?

I have looked in the Expect manpage and Googled it, but I have not found what the -r for expect is. I saw this option used before like this

expect -r "\r\n\r\n"

in an expect script, but can't figure out what it's for. Does anyone know where I can look to find this answer? Thanks in advance

Upvotes: 0

Views: 729

Answers (1)

pynexj
pynexj

Reputation: 20698

This also confused me a bit when I saw someone was using expect -regexp PATTERN because in the man page it only mentions expect -re PATTERN. I tried expect -regexp PATTERN and it indeed works.

At some time I downloaded Expect's source code and took a look and found out the reason.

In the source code (see the function parse_expect_args() in expect.c), the expect's options are actually defined as follows:

static char *flags[] = {
    "-glob", "-regexp", "-exact", "-notransfer", "-nocase",
    "-i", "-indices", "-iread", "-timestamp", "-timeout",
    "-nobrace", "--", (char *)0
};

then in the function it calls Tcl's Tcl_GetIndexFromObj(interp, objPtr, tablePtr, msg, flags, indexPtr) to parse command options. Accordint to Tcl_GetIndexFromObj()'s manual:

... a match occurs if objPtr's string value is identical to one of the strings in tablePtr, or if it is a non-empty unique abbreviation for exactly one of the strings in tablePtr and the TCL_EXACT flag was not specified; ...

Here Expect calls Tcl_GetIndexFromObj() with flags = 0 (no TCL_EXACT) so the documented -gl, -re and -ex in the man page are actually -glob, -regexp and -exact respectively. And since there's only one option -regexp starting with -r so -r just means the same as -regexp (and -re).

Personally I recommend the documented options still be used to avoid confusing other people.

Upvotes: 5

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