sleep - Linux

Overview

The sleep command in Linux is used to pause the execution of a script or a command for a specified period of time. This command is primarily useful in shell scripts or when executing a batch of commands sequentially, allowing time-dependent processes to complete or delays to be introduced.

Syntax

The basic syntax of the sleep command is:

sleep NUMBER[SUFFIX]

NUMBER can be an integer or floating-point number.
SUFFIX is an optional specifier for time units. If no suffix is used, the default is seconds (s). Available suffixes include:
- s for seconds
- m for minutes
- h for hours
- d for days

Multiple arguments can be used together to specify complex times. For example, sleep 2h 30m would pause for 2 hours and 30 minutes.

Options/Flags

The sleep command has very few options:

--help: Display a help message and exit.
--version: Output version information and exit.

Examples

Basic Sleeping
Pause a script for 10 seconds:
```
sleep 10
```
Multiple Time Periods
Pause for 2 minutes and 15 seconds:
```
sleep 2m 15s
```
Floating-Point Numbers
Pause for 1.5 seconds:
```
sleep 1.5
```

Script Delays
Using sleep in a bash script to delay loops:

for i in {1..5}; do
    echo "Iteration $i"
    sleep 1s
done

Common Issues

Non-numeric Arguments: If non-numeric characters are included without a proper suffix, sleep will throw an error. Always specify time with correct numbers and suffixes.
Long Sleep Intervals: Using very long sleep intervals might make it seem like the script is stuck.

Integration

The sleep command can be integrated with other Linux commands to manage timing effectively:

#!/bin/bash
echo "Waiting for database to start."
sleep 10s
echo "Checking database status."
# Place a command here to check database status.

Combine sleep with loops for repeated checks:

#!/bin/bash
until ping -c 1 example.com; do
    echo "Waiting for 'example.com' to respond..."
    sleep 5s
done

wait: Waits for a process to change state.
timeout: Runs a command with a time limit.

For further reading and more detailed information, visit the official Linux man pages online.