bash-com/README.md

# bash socket utility

## 1. Listen

Binding an input creates a listening socket on a local port and binds the socket data to a local accessible buffer (accessible with the native `read` call).

```bash
bind-input $id $port;
```

*Arguments:*
- `$id` is a unique arbitrary name you must give to the listening binding
- `$port` is the number of the local port to listen to (between 1024 and 49151)

*Execution:*
- The `bind-input` execution will last until the socket is created, then it will move it to a background process and print its *PID*.
- In order to close properly the `bind-input`, you must kill its *PID* with one of the 3 following signals: SIGINT, SIGHUP, SIGTERM. Note that you must not use *SIGKILL* because it won't trigger the "*proper closing*" routine.


*Exemple:*

Let's say that you want to listen to port 9999, then read every second. You want to ignore empty messages (if nothing received), and end the program when you receive the message "**END**".

```bash
#/bin/bash

# 1. Create the listening socket + store PID in /tmp
bind-input input1 9999 > /tmp/get_bg_pid;

# 2. Store PID in a variable
bound_pid="`cat /tmp/get_bg_pid`";

# 3. Now the socket is listening, you can read every 1 sec
while true; do

	# 3.1. Read received data from port 9999
	message="`read input1`";

	# 3.2. Ignore empty messages
	[[ -z "$message" ]] && sleep 1 && continue;

	# 3.3. Exit while() loop if received "END"
	[[ "$message" = "END" ]] && break;

	# 3.4. Wait 1 sec
	sleep 1;

done;

# 4. Kill 'bind-input' with signal SIGINT, SIGHUP or SIGTERM
kill -INT $bound_pid;
```










## 2. Connect

Binding an output creates a local accessible buffer (accessible with the native `write` call) bound to a socket connecting to a certain host and port.

```bash
bind-output $id $host $port;
```

*Arguments:*
- `$id` is a unique arbitrary name you must give to the output binding
- `$host` is the hostname (IP addr. or resolvable) of the machine to connect to.
- `$port` is the number of the remote port to connect to (between 1024 and 49151)

*Execution:*
- The `bind-output` execution will last until the socket is created, then it will move it to a background process and print its *PID*.
- In order to close properly the `bind-output`, you must kill its *PID* with one of the 3 following signals: SIGINT, SIGHUP, SIGTERM. Note that you must not use *SIGKILL* because it won't trigger the "*proper closing*" routine.


*Exemple:*

Let's say that you want to connect to port 192.168.0.2 at port 9999, wait 2 seconds, send a message, wait 1 second and send the "**END**" message.

```bash
#/bin/bash

# 1. Create the connecting socket + store PID in /tmp
bind-output output1 192.168.0.2 9999 > /tmp/get_bg_pid;

# 2. Store PID in a variable
bound_pid="`cat /tmp/get_bg_pid`";

# 3. Wait for sending first message
sleep 2;
write output1 "some message\nwith\tescapable\e[1mcharaters\e[0m";

# 4. Wait for sending "END" message
sleep 1;
write output1 "END";

# 5. Kill 'bind-output' with signal SIGINT, SIGHUP or SIGTERM
kill -INT $bound_pid;
```

## 3. Network trigger

The programs `trigger-send` and `trigger-wait` allows *signals* to be send over the network (private or public).
- `trigger-wait` will wait for a signal to exit.
- `trigger-send` will send a signal to a remote host.

### **trigger-wait**

```bash
trigger-wait $key $port
```

*Arguments:*
- `$key` is a secret string that the sender will have to match.
- `$port` is the local listening port (between 1024 and 49151).

*Note:* The reading delay is set to 0.5 seconds not to overuse the processor.

*Exemple:*

Let's say you want to wait for a signal on port 9999 then launch some command (for example `read input1`).

```bash
trigger-wait somekey123 9999; read input1;
```

### **trigger-send**

```bash
trigger-wait $key $host $port
```

*Arguments:*
- `$key` is the same secret string used by the receiver.
- `$host` is the remote hostname (IP addr. or resolvable) to send the messag eto.
- `$port` is the remote port to send the message to (between 1024 and 49151).

*Exemple:*

Let's say you want to execute a long command (sleep 5), then send the trigger to 192.168.0.2 port 9999.

```bash
sleep 5; trigger-send somekey123 192.168.0.2 9999;
```