[gogo] result of commands is implicitly written to pipe
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Key: FELIX-1474
URL: https://issues.apache.org/jira/browse/FELIX-1474
Project: Felix
Issue Type: Bug
Components: Gogo
Reporter: Derek Baum
Priority: Minor
RFC132 commands are designed to be easy to create, allowing direct use of
System.out
void echo1(String[] args) {
StrinbgBuilder buf = new StringBuilder();
for (String arg : args) {
if (buf.length() > 0)
buf.append(' ');
buf.append(arg)
}
System.out.println(buf.toString());
}
but it also allows commands that return values:
String echo2(String[] args) {
StrinbgBuilder buf = new StringBuilder();
for (String arg : args) {
if (buf.length() > 0)
buf.append(' ');
buf.append(arg)
}
return(buf.toString());
}
Both these command cause grep to match 'hello':
% echo1 hello | grep hello
% echo2 hello | grep hello
This is expected with echo1, as it writes to System.out.
It is more surprising that echo2 also works, as it doesn't write to System.out.
In this case, the runtime is implicitly writing the result of 'echo2 hello'
into the pipe.
This is convenient, as it lets commands that don't write to System.out be used
in pipelines.
However, it can also get in the way.
I have a grep command that writes to System.out and returns a boolean,
depending on whether it matched:
% bundles | grep felix | wc
but in this case, the wc command gets the output from grep and also the result
of grep (true) which not wanted,
so I would like some way of disabling this behaviour.
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