log

Run a command every n seconds. See cumulative outputs (one run by line) in terminal and/or write to disk.

log is a barebone alternative to watch, better suited for longitudinal monitoring, logging, etc.

0. Install

log is one file with 20 useful lines of Bash logic.

1. Either clone the repo 1iis/log,
   or download the log file (remove the .txt extension GH adds).

2. Put the file in your PATH. Pick one:

sudo cp -v log.sh /usr/local/bin/log  # Copy file

or

sudo nano /usr/local/bin/log   # Create file, then:
# - paste code (Shift+Ctrl+V) from 2. Source
# - save (Ctrl+O, Enter)
# - exit (Ctrl+X)

Make it executable.

chmod +x /usr/local/bin/log

Warning

If you use Zsh, log is a built-in function to compute natural $ln$.
If if you don't need to do such math in your shell, you can disable it, thereby letting /usr/local/bin/log be found by which log, and run as expected.

disable log       # ONLY for Zsh

1. Usage

One file: log, a Bash script.

Syntax

log [-v] [-n SECONDS] [-o FILE] [-t] [-h] <command>

Exit with Ctrl + C.

Important

-v is a toggle:

• Without it: log writes output to <command>.log (you see nothing)
• With it: log prints output to terminal (no file written)

Use -v -o FILE to both see outputs in the terminal and write to FILE.

Options

Flag	Description
-v	Print output to terminal. If absent, writes to disk.
-n SECONDS	Interval in SECONDS (default: 1).
-o FILE	Log output to FILE (only if -o used).
-t	Prepend each line with Unix timestamp.
-h, --help	Show help message and exit.

Examples

Basic usage: log writes to <command>.log.

log date  # wait a few seconds
^C        # CTRL+C to interrupt the process

# after four seconds
cat date.log
Tue Apr 28 14:14:33 UTC 2026
Tue Apr 28 14:14:34 UTC 2026
Tue Apr 28 14:14:35 UTC 2026
Tue Apr 28 14:14:36 UTC 2026

-v prints to terminal, no write to file.

log -v date
Tue Apr 28 14:14:51 UTC 2026
Tue Apr 28 14:14:52 UTC 2026
...

-t for timestamps.

log -tv date  # Unix timestamps
[1777386029] Tue Apr 28 14:20:29 UTC 2026
[1777386030] Tue Apr 28 14:20:30 UTC 2026
...

Write the output of date with Unix timestamps to both terminal (-v) and to a file of our choice (-o /my/file.log).

log -t -v -o /my/file.log date
[1777386138] Tue Apr 28 14:22:18 UTC 2026
[1777386139] Tue Apr 28 14:22:19 UTC 2026
^C

cat /my/file.log
[1777386138] Tue Apr 28 14:22:18 UTC 2026
[1777386139] Tue Apr 28 14:22:19 UTC 2026

log in the background to retrieve usage of the terminal session.

log date &  # pipe with `&` to run process in the background

# do what you want
whoami
pwd
# ...

fg              # retrieve control of the background process
^C              # Ctrl+C to interrupt the process
cat date.log    # check that logging worked
Thu Apr 30 08:38:32 CEST 2026
Thu Apr 30 08:38:33 CEST 2026
Thu Apr 30 08:38:34 CEST 2026
Thu Apr 30 08:38:35 CEST 2026