when

#!/usr/bin/expect --
package require cmdline

set options {
    {q          "quite: do not echo ouput from cmd to stdout"}
}
set usage "'when' runs a command until a pattern is emitted\n\
\nexample:\nwhen f280 log hexdump /dev/urandom\n\n\
options:\n\
usage: when \[options] PATTERN LOGFILE COMMAND \[ARGS\]"

if { [catch { array set params [::cmdline::getoptions argv $options $usage] } ERR ] } {
    puts $ERR
    exit -1
}

if {[llength $argv] < 4} {
    puts [::cmdline::usage $options $usage]
    exit 1
}

set pattern [ lindex $argv 0 ]
set logfile [ lindex $argv 1 ]
set command [lreplace $argv 0 1]

set timeout 3600
log_file -a -noappend $logfile
if { $params(q) } { log_user 0 }

eval spawn $command

expect -re "$pattern" {
    exit 0
}

exit 1