Sending AT commands via socat and chat

In order to send AT commands via socat and chat (usually from ppp-chat package):

1. Create chat script:

   sim900-init.chat:

   "" AT
   OK AT+CLVL=100
   OK AT+CMIC=0,0
   OK AT+ECHO=0,0,0,0
   OK AT+SIDET=0,0
   OK
   

2. Create bash scipt:

   sim900-init.sh:

   #!/bin/sh
   
   # IOCTL: Put the terminal into exclusive mode
   TIOCEXCL=0x540c
   
   socat -d \
       file:/dev/ttyUSB0,ioctl-void=$TIOCEXCL,flock-ex-nb,b115200,csize=3,cstopb=0,crtscts=0,clocal=1,cfmakeraw,nonblock,crnl \
       exec:'/usr/sbin/chat -v -t 5 -s -f sim900-init.chat',pty
   

3. Run created script:

   It is a good idea to run this script as non-root:

   chmod +x sim900-init.sh
   ./sim900-init.sh
   

   Output (echo is on):

   send (AT^M)
   expect (OK)
   AT
   OK
    -- got it
   
   send (AT+CLVL=100^M)
   expect (OK)
   
   AT+CLVL=100
   OK
    -- got it
   
   send (AT+CMIC=0,0^M)
   expect (OK)
   
   AT+CMIC=0,0
   OK
    -- got it
   
   send (AT+ECHO=0,0,0,0^M)
   expect (OK)
   
   AT+ECHO=0,0,0,0
   OK
    -- got it
   
   send (AT+SIDET=0,0^M)
   expect (OK)
   
   AT+SIDET=0,0
   OK
    -- got it
   

Manual pages.

• chat.
• socat.

---

If your software still uses lock files for serial ports shell script should be modified:

#!/bin/sh

socat -d \
    file:/dev/ttyUSB0,lockfile=/var/lock/LCK..ttyUSB0,b115200,csize=3,cstopb=0,crtscts=0,clocal=1,cfmakeraw,nonblock,crnl \
    exec:'/usr/sbin/chat -v -s -f sim900-init.chat',pty