[WIP]:Return value of pgrep is incorrect on RHEL6

Issue

• The return value of pgrep command on RHEL6.4 is different from previous versions and description in man page.

On RHEL5.X

$ uname -r
2.6.18-348.el5
$ pgrep -u root brabrabra bra
Usage: pgrep [-flvx] [-d DELIM] [-n|-o] [-P PPIDLIST] [-g PGRPLIST]
[-s SIDLIST]
      [-u EUIDLIST] [-U UIDLIST] [-G GIDLIST] [-t TERMLIST]
[PATTERN]
$ echo $?
2

On RHEL6.X

# uname -r
2.6.32-358.el6.x86_64
# pgrep -u root brabrabra bra
Usage: pgrep [-flvx] [-d DELIM] [-n|-o] [-P PPIDLIST] [-g PGRPLIST]
[-s SIDLIST]
      [-u EUIDLIST] [-U UIDLIST] [-G GIDLIST] [-t TERMLIST]
[PATTERN]
# echo $?
0

We consider the return value above should be 2
instead of 0.

A manpage of pgrep says:

EXIT STATUS
     0  One or more processes matched the criteria.

     1  No processes matched.

     2  Syntax error in the command line.

     3  Fatal error: out of memory etc

So the return value of 6.X is incorrect.