On Fri, Mar 02, 2007 at 04:37:37AM EST, Bhasker C V wrote: > I have logname command give me this output > [EMAIL PROTECTED] ~]$ logname > bhaskerv > > and say i execute this command > > [EMAIL PROTECTED] ~]$ echo `logname` > bhaskerv > > till this it is all fine > > BUT > [EMAIL PROTECTED] ~]$ who | grep `logname` > logname: no login name > Usage: grep [OPTION]... PATTERN [FILE]... > Try `grep --help' for more information. > > is there anything i am doing wrong ?
bash man page: "Each command in a pipeline is executed as a separate process (i.e., in a subshell)." The problem appears to be that the subshell where `logname` executes is not a login shell. Here are a few commands I issued from the linux console that may help clarify: $ logname myuser $ logname 1>&2 | logname # redirect stdout to stderr myuser # 1st instance of logname logname: no login name # 2nd instance of logname The 1st logname command is successful. The 2nd logname command executes in a subshell and returns the message you reported. $ logname | logname 2> /dev/null # returns nothing The 2nd instance of logname writes an error message to stderr and nothing to stdout. As a result, $ who | grep `logname` ends up as: $ who | grep .. resulting in a syntax error. Another angle of approach is that the logname command can only return the login name as long as the calling process added an entry to the utmp file (see info coreutils logname) .. If not, it fails and displays the "logname: no login name" message. I guess it would not make much sense having all subshells invoked during an interactive session create/remove entries to/from the /var/run/utmp file. Thanks, cga -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
