Richard Suchenwirth 2014-10-07 - The global env array can be used to pass parameters into a script. In Unixoid shells, you can set a temporary env variable in front of a command:
/etc/us/trecs/fss $ FOO=2 echo hello hello /etc/us/trecs/fss $ echo $FOO
From inside a Tcl script, you can check if a particular environment variable exists, and use it:
if [info exists ::env(FOO)] {set foo $::env(FOO)} else {set foo ""}
As a variation, programs like awk also accept such variables in the argument list:
$ awk '{print $1}' FS=, input.txt
The following function finds, applies and removes such specifications from an argument list:
proc getenv _argv { upvar 1 $_argv argv global env foreach arg $argv { if [regexp {([A-Za-z0-9_]+)=(.+)} $arg -> var val] { set env($var) $val set pos [lsearch -exact $argv $arg] set argv [lreplace $argv $pos $pos] } } }
Testing in an interactive tclsh:
% set argv {foo FS=, bar} foo FS=, bar % getenv argv % set argv foo bar % set env(FS) ,