1SyncExec(3)           User Contributed Perl Documentation          SyncExec(3)
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NAME

6       Proc::SyncExec - Spawn processes but report exec() errors
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SYNOPSIS

9           # Normal-looking piped opens which properly report exec() errors in $!:
10           sync_open WRITER_FH, "|command -with args" or die $!;
11           sync_open READER_FH, "command -with args|" or die $!;
12
13           # Synchronized fork/exec which reports exec errors in $!:
14           $pid = sync_exec $command, @arg;
15           $pid = sync_exec $code_ref, $cmd, @arg;     # run code after fork in kid
16
17           # fork() which retries if it fails, then croaks() if it still fails.
18           $pid = fork_retry;
19           $pid = fork_retry 100;              # retry 100 times rather than 5
20           $pid = fork_retry 100, 2;           # sleep 2 rather than 5 seconds between
21
22           # A couple of interfaces similar to sync_open() but which let you
23           # avoid the shell:
24           $pid = sync_fhpopen_noshell READERFH, 'r', @command;
25           $pid = sync_fhpopen_noshell WRITERFH, 'w', @command;
26           $fh = sync_popen_noshell 'r', @command_which_outputs;
27           $fh = sync_popen_noshell 'w', @command_which_inputs;
28           ($fh, $pid) = sync_popen_noshell 'r', @command_which_outputs;
29           ($fh, $pid)= sync_popen_noshell 'w', @command_which_inputs;
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DESCRIPTION

32       This module contains functions for synchronized process spawning with
33       full error return.  If the child's exec() call fails the reason for the
34       failure is reported back to the parent.
35
36       These functions will croak() if they encounter an unexpected system
37       error, such as a pipe() failure or a repeated fork() failure.
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39       Nothing is exported by default.
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41       fork_retry [max-retries [sleep-between]]
42           This function runs fork() until it succeeds or until max-retries
43           (default 5) attempts have been made, sleeping sleep-between seconds
44           (default 5) between attempts.  If the last fork() fails fork_retry
45           croak()s.
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47       sync_exec [code] command...
48           This function is similar to a fork()/exec() sequence but with a few
49           twists.
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51           sync_exec does not return until after the fork()ed child has
52           already performed its exec().  The synchronization this provides is
53           useful in some unusual circumstances.
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55           Normally the pid of the child process is returned.  However, if the
56           child fails its exec() sync_exec returns undef and sets $! to the
57           reason for the child's exec() failure.
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59           Since the @cmd array is passed directly to Perl's exec() Perl might
60           choose to invoke the command via the shell if @cmd contains only
61           one element and it looks like it needs a shell to interpret it.  If
62           this happens the return value of sync_exec only indicates whether
63           the exec() of the shell worked.
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65           The optional initial code argument must be a code reference.  If it
66           is present it is run in the child just before exec() is called.
67           You can use this to set up redirections or whatever.  If code
68           returns false no exec is performed, instead a failure is returned
69           using the current $!  value (or EINTR if $! is 0).
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71           If the fork() fails or if there is some other unexpected system
72           error sync_exec croak()s rather than returning.
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74       sync_fhpopen_noshell fh type cmd [arg]...
75           This is a popen() but it never invokes the shell and it uses
76           sync_exec() under the covers.  See "sync_exec".
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78           The type is either 'r' to read from the process or 'w' to write to
79           it.
80
81           The return value is the pid of the forked process.
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83       sync_popen_noshell type cmd arg...
84           This is like sync_fhpopen_noshell, but you don't have to supply the
85           filehandle.
86
87           If called in an array context the return value is a list consisting
88           of the filehandle and the PID of the child.  In a scalar context
89           only the filehandle is returned.
90
91       sync_open fh [open-spec]
92           This is like a Perl open() except that if a pipe is involved and
93           the implied exec() fails sync_open() fails with $! set
94           appropriately.  See "sync_exec".
95
96           Like sync_exec, sync_open croak()s if there is an unexpected system
97           error (such as a failed pipe()).
98
99           Also like sync_exec, if you use a command which Perl needs to use
100           the shell to interpret you'll only know if the exec of the shell
101           worked.  Use sync_fhpopen_noshell or sync_exec to be sure that this
102           doesn't happen.
103

AUTHOR

105       Roderick Schertler <roderick@argon.org>
106

SEE ALSO

108       perl(1).
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112perl v5.30.1                      2020-01-30                       SyncExec(3)