lps2lts no longer outputs to stdout by default about mcrl2 HOT 3 CLOSED

The expected behaviour you describe is indeed how most tools behave. I think that an exception was made for lps2lts because in some cases it is desirable to only use one of the other features of lps2lts (counting states, finding deadlocks etc.) and not output anything (because this can be expensive, in time or disk space). Of course this design decision can be changed, I think @jgroote's opinion is relevant.

from mcrl2.

The tool description notes a default output:

$ lps2lts -h
Usage: lps2lts [OPTION]... [INFILE [OUTFILE]]
Transforms the LPS in INFILE and writes a corresponding LTS  to OUTFILE. If 
OUTFILE is not present, stdout is used. If INFILE is not  present, stdin is 
used.

from mcrl2.

Thank you for the input @tneele.

After discussion with @jgroote, we concluded that by default there should be no LTS output to stdout. Only if the output format is specified, the default output should be stdout.

A documentation update and a fix is needed for some output formats:

$ echo "act a; proc P = a . P; init P;" | mcrl22lps | lps2lts -olts                                   
[error]   Fail to open file  for writing.
$ echo "act a; proc P = a . P; init P;" | mcrl22lps | lps2lts -oaut
[error]   cannot open '' for writing
$ echo "act a; proc P = a . P; init P;" | mcrl22lps | lps2lts -ofsm
---
---
1 1 "a"
$ echo "act a; proc P = a . P; init P;" | mcrl22lps | lps2lts -odot
cannot open DOT file '' for writing.

from mcrl2.