从 perl 中的系统命令捕获退出代码

Question

how can we capture the exit code correctly when we call a command via 'system'? from the testcase below i consistently capture "-1" which the expectation is "0" for code1 and "1" for code2.

test1.pl

use feature qw(say);
use strict;

my $code = system("./test2.pl 0");
say "code1  = $code";
system("./test2.pl 0");
say "code1' = $?";

$code = system("./test2.pl 1");
say "code2  = $code";
system("./test2.pl 1");
say "code2' = $?";

test2.pl

use feature qw(say);

use strict;

say "arg = @ARGV[0]";
my $exit_code = @ARGV[0];
say "this is a dummy script which exit with $exit_code";
exit $exit_code;

Output:

% ./project_r/test.pl
code1 = -1
code1' = -1
code2 = -1
code2' = -1

Answer 1

As per the documentation for system , -1 indicates there was a problem trying to execute the command, and that the error message is found in $! .

system(...);
die("Can't run test2: $!\n") if $? == -1;
die("test2 killed by signal ".( $? & 0x7F )."\n") if $? & 0x7F;
die("test2 exited with error ".( $? >> 8 )."\n") if $? >> 8;
say("Child completed successfully.");

As you can see by the lack of output of this is a dummy , your program never ran.

Likely culprits are:

• The path doesn't refer to an existing file.
• The file isn't executable.

A missing shebang ( #! ) line could render a file non-executable, but I'm presuming you simply left out the shebang lines from your snippets for conciseness (since ./project_r/test.pl wouldn't run otherwise).

I'm also assuming that the difference in the name of the file you posted ( test1.pl ) and the file you executed ( test.pl ) isn't relevant.

My best guess is that test2.pl is in the same directory as test.pl / test1.pl , which isn't the current directory but a subdircetory of the current directory named project_r .

Fix:

use FindBin qw( $RealBin );

my $code = system("$RealBin/test2.pl", "0");

Answer 2

Note that if you are going to run other Perl programs from a Perl program, you need to use the same settings. Otherwise you might run into situations where you are using a different perl with your parent perl 's settings:

Your current Perl is in $^X :

system $^X, 'test2.pl', '0';