Open file

2 snippets across 2 stacks — Bash & Linux, Python

Also written as open files

SHBash & Linux

List Open Files & Ports

syntax

lsof [options]

example

lsof -i :3000
lsof -u deploy
lsof +D /var/log/

output

COMMAND   PID   USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    19283 deploy   22u  IPv4  284719      0t0  TCP *:3000 (LISTEN)

Note -i :port shows which process is using a port (essential for resolving 'address already in use' errors). -u filters by user. +D lists all open files within a directory. Requires root for other users' processes.

PYPython

Reading Files

PY · File I/O

syntax

with open(path, 'r') as f:
    content = f.read()

example

with open("config.txt", "r", encoding="utf-8") as f:
    content = f.read()
    print(content[:50])

# Read line by line (memory efficient)
with open("data.log") as f:
    for line in f:
        print(line.strip())

Note Always specify encoding='utf-8' explicitly. The default varies by platform. Iterating line-by-line avoids loading the entire file into memory.