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ActiveTcl User Guide |
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Command line arguments and environment
strings
Scripts are much more useful if they can be called with
different values in the command line.
For instance, a script that extracts a particular value from a
file could be written so that it prompts for a file name, reads the
file name, and then extracts the data. Or, it could be written to
loop through as many files as are in the command line, and extract
the data from each file, and print the file name and data.
The second method of writing the program can easily be used from
other scripts. This makes it more useful.
The number of command line arguments to a Tcl script is passed
as the global variable argc . The name
of a Tcl script is passed to the script as the global variable
argv0 , and the rest of the command
line arguments are passed as a list in argv. The name of the executable that runs the
script, such as tclsh is given by the
command info nameofexecutable
Another method of passing information to a script is with
environment variables. For instance, suppose you
are writing a program in which a user provides some sort of comment
to go into a record. It would be friendly to allow the user to edit
their comments in their favorite editor. If the user has defined an
EDITOR environment variable, then you
can invoke that editor for them to use.
Environment variables are available to Tcl scripts in a global
associative array env . The index into
env is the name of the environment
variable. The command puts "$env(PATH)" would
print the contents of the PATH
environment variable.
Example
puts "There are $argc arguments to this script"
puts "The name of this script is $argv0"
if {$argc > 0} {puts "The other arguments are: $argv" }
puts "You have these environment variables set:"
foreach index [array names env] {
puts "$index: $env($index)"
}
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