Sonic Linux

 1.command -v

root@leaf2:/tmp# command -v supervisorctl
/usr/local/bin/supervisorctl
root@leaf2:/tmp# command -v ls
/usr/bin/ls

2.vtysh -f /etc/frr/frr.conf

equivalent to

vtysh
conf t
<all config lines from file>

3.vtysh -c "show bgp summary"

4.File Descriptors in Linux

What is a File Descriptor?
A file descriptor (FD) is just a number that Linux uses to represent an open I/O stream. Everything in Linux is treated as a file — including input, output, and errors.
The 3 Standard File Descriptors
Number          Name          Meaning                     Default destination

0                      stdin           Standard Input           Keyboard

1                      stdout        Standard Output        Terminal screen

2                       stderr        Standard Error            Terminal screen

Example:-

2>/dev/null     # FD2 → /dev/null (file)

2>out.txt       # FD2 → out.txt (file)

2>&1            # FD2 → FD1 (file descriptor, because of &)