function::pid - Linux
Overview
The pid
function is a Shell Built-in command that converts a given number or variable to an integer, ensuring it represents a valid process ID (PID). It is commonly utilized to validate and work with PIDs in scripts or command pipelines.
Syntax
pid [-s] [-w] <number-or-variable>
Options/Flags
-s
: Prevent errors by returning an empty string on invalid PIDs (default behavior).-w
: Consider any integer argument as a PID (even those outside the valid range).
Examples
- Check if a PID is valid:
if pid 1234; then
echo "Valid PID"
else
echo "Invalid PID"
fi
- Convert a variable to an integer PID:
pid_str="1234"
pid $pid_str
- Parse a PID from a command’s output:
pid=$(ps -ef | grep my_process | awk '{print $2}')
Common Issues
- Out-of-range PIDs: By default,
pid
detects PIDs outside the valid range (0-32768). Use-w
for more flexibility. - Empty string result: If
-s
is not used, an invalid PID will result in an error.
Integration
pid
can be used in conjunction with other commands to:
- Validate PIDs before sending signals:
if pid $pid; then kill -9 $pid; fi
- Extract PIDs from process listings:
ps -ef | grep my_process | awk '{print pid $2}'
- Create scripts that interact with running processes: Combine
pid
withpgrep
,pkill
, and other process-related commands.
Related Commands
kill
: Send signals to processes based on PID.ps
: List running processes and their PIDs.pgrep
: Find processes based on name or pattern.