### NAME

pid - Retrieve process identifiers

### SYNOPSIS

pid ?fileId?

### DESCRIPTION

If the fileId argument is given then it should normally refer to a process pipeline created with the open command. In this case the pid command will return a list whose elements are the process identifiers of all the processes in the pipeline, in order. The list will be empty if fileId refers to an open file that isn't a process pipeline. If no fileId argument is given then pid returns the process identifier of the current process. All process identifiers are returned as decimal strings.

### EXAMPLE

Print process information about the processes in a pipeline using the SysV ps program before reading the output of that pipeline:

    set pipeline [open "| zcat somefile.gz | grep foobar | sort -u"]
    # Print process information
    exec ps -fp [pid $pipeline] >@stdout
    # Print a separator and then the output of the pipeline
    puts [string repeat - 70]
    puts [read $pipeline]
    close $pipeline

### SEE ALSO

exec, open

### KEYWORDS

file, pipeline, process identifier

    Copyright © 1993 The Regents of the University of California.
    Copyright © 1994-1996 Sun Microsystems, Inc.
    Copyright © 1995-1997 Roger E. Critchlow Jr.