---
name: "pid"
section: "3tcl"
platform: "linux"
package: "tcl8.6-doc"
version: "8.6.16+dfsg-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/pid"
---

# pid(3tcl)

Retrieve process identifiers

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## NAME

pid - Retrieve process identifiers

## SYNOPSIS

**pid** ?*fileId*?

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```

## 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 is not 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(3tcl)](/exec/3tcl.md), [open(3tcl)](/open/3tcl.md)

## KEYWORDS

file, pipeline, process identifier