I've run into similar FRR CLI automation headaches before—interactive terminals are a pain to handle in scripts, but there are two reliable workarounds that let you automate this without relying on manual terminal input.

Method 1: Use Multiple -c Arguments with vtysh #

FRR's vtysh supports passing multiple commands via repeated -c flags. Each flag maps to one command you'd enter manually, and vtysh executes them in sequence while preserving the CLI context (like automatically staying in config-bfd mode after running bfd).

Here's a Python script using subprocess to implement this:

import subprocess

# Define the exact sequence of commands you'd run in vtysh
frr_commands = [
    "configure",
    "bfd",
    "peer 10.6.5.8",
    "do show bfd peers"
]

# Build the full vtysh command with repeated -c arguments
vtysh_command = ["vtysh"]
for cmd in frr_commands:
    vtysh_command.extend(["-c", cmd])

# Execute the command and capture output
result = subprocess.run(vtysh_command, capture_output=True, text=True)

# Print results to verify success
print("Command Output:\n", result.stdout)
if result.stderr:
    print("Errors:\n", result.stderr)

Method 2: Load Commands from a Temporary File #

For longer or more complex config sequences, it's cleaner to write commands to a temporary file and load it with vtysh -f:

import subprocess
import tempfile
import os

# Define your FRR configuration as a multi-line string
config_script = """configure
bfd
peer 10.6.5.8
do show bfd peers
"""

# Create a temporary file to hold the config commands
with tempfile.NamedTemporaryFile(mode='w', delete=False) as temp_file:
    temp_file.write(config_script)
    temp_path = temp_file.name

try:
    # Run vtysh with the temporary config file
    result = subprocess.run(["vtysh", "-f", temp_path], capture_output=True, text=True)
    print("Command Output:\n", result.stdout)
    if result.stderr:
        print("Errors:\n", result.stderr)
finally:
    # Clean up the temporary file after execution
    os.unlink(temp_path)

Why Your Previous Attempts Failed #

• Running run_command("vtysh") launches an interactive terminal, which pauses your script until the terminal is closed—this can't handle automated command input.
• Using a single -c with semicolon-separated commands (like vtysh -c "configure; bfd; peer 10.6.5.8") usually fails because FRR's CLI doesn't handle context switches correctly with semicolons. The multi--c or file-based approach mimics manual input properly, keeping the CLI context intact as you move between sub-modes.

Note on Permissions #

If your user doesn't have direct access to vtysh, add sudo to the command list (e.g., ["sudo", "vtysh"] instead of just ["vtysh"]). You may need to set up passwordless sudo for the script's user to avoid interactive password prompts.

内容的提问来源于stack exchange，提问作者Riya Singh