Usage Messages

Choose a usage message when a command is missing.

usage-messages A usage message explains the expected command shape. Programs commonly show it when required input is missing.

has_command has_command = 0 (default)has_command = 1

usage_messages.pl

Replay: real traced execution (multi-file project)

use strict;
use warnings;

my $has_command = 0;
my $status = $has_command ? "ready" : "needs-help";
my $message = $has_command ? "run command" : "usage: tool command";

print "has_command=$has_command\n";
print "status=$status\n";
print "message=$message\n";

use strict;
use warnings;

my $has_command = 1;
my $status = $has_command ? "ready" : "needs-help";
my $message = $has_command ? "run command" : "usage: tool command";

print "has_command=$has_command\n";
print "status=$status\n";
print "message=$message\n";

$has_command ← 0, $status ← needs-help, $message ← usage: tool command

⋯4my $has_command→ 0 = 0; #@has_command=15my $status→ needs-help = $has_command0 ? "ready" : "needs-help";6my $message→ usage: tool command = $has_command0 ? "run command" : "usage: tool command";78print "has_command=$has_command0\n";9print "status=$statusneeds-help\n";10print "message=$messageusage: tool command\n";⋯

outputhas_command=0
status=needs-help
message=usage: tool command

$has_command ← 1, $status ← ready, $message ← run command

⋯4my $has_command→ 1 = 1;5my $status→ ready = $has_command1 ? "ready" : "needs-help";6my $message→ run command = $has_command1 ? "run command" : "usage: tool command";78print "has_command=$has_command1\n";9print "status=$statusready\n";10print "message=$messagerun command\n";⋯

outputhas_command=1
status=ready
message=run command