Unix commands I need often

but which are tedious to work anew out each time

November 6, 2015 — September 15, 2023

computers are awful
macos
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posix
Figure 1: Invocations and commands

General, not macOS-specific or Linux-specific. I try to cover mostly standard commands here but sometimes the features of the invoking shell are also important. You could optimise that also, e.g. by switching from bash to fish or PowerShell.

1 Modernization

Why do we stick to the classic 80s Unix tools? mhoye recommends updating standard CLI utilities, as does Benjamin Pollack. Edited highlights from those post dominate this page.

Improvements on “classic” tools and utilities:

  • ripgrep, a line-oriented search tool that recursively searches the current directory for a regex pattern described as a better grep.

  • sd, “Intuitive find & replace CLI (sed alternative)

  • fd, a “A simple, fast and user-friendly alternative to ‘find’”

  • The moreutils collection. Editied highlights:

    • chronic: runs a command quietly unless it fails
    • combine: combine the lines in two files using boolean operations
    • errno: look up errno names and descriptions
    • ifdata: get network interface info without parsing ifconfig output
    • ifne: run a program if the standard input is not empty
    • isutf8: check if a file or standard input is utf-8
    • lckdo: execute a program with a lock held
    • mispipe: pipe two commands, returning the exit status of the first
    • parallel: run multiple jobs at once
    • pee: tee standard input to pipes
    • sponge: soak up standard input and write to a file (allows us to pipe to and from the same file)
    • ts: timestamp standard input
    • vidir: edit a directory in your text editor
    • vipe: insert a text editor into a pipe
    • zrun: automatically uncompress arguments to command
  • ripgrep / angle-grinder etc search through files

  • atool, a set of scripts that wrap common compressed-file-format handlers.

  • bat, a “better cat”.

  • lsd and exa, both new takes on the venerable ls.

  • There’s also zoxide: an interesting update to, of all things, cd!

  • Broot: better navigation of directory trees.

  • mcfly: McFly replaces your default ctrl-r shell history search with an intelligent search engine that takes into account your working directory and the context of recently executed commands. McFly’s suggestions are prioritized in real time with a small neural network.

There are many more under text data processing.

2 Resource monitoring

  • htop, “a cross-platform interactive process viewer.” An htop-like utility called bottom also got some votes.

    As an aside, about htop: one commenter noted that they run HTOP on a non-interactive TTY, something like control-alt-F11; so do I, and it’s great, but you must not do this on sec-critical systems. You can kill processes through htop, and that gives you a choice of signals to issue, and on most machines running systemd systemd init responds to SIGTRMIN+1 by dropping back into rescue mode, and that’s a backstage pass to a root shell. I have used this to recover a personal device from an interrupted upgrade that broke PAM. You must never do this on a machine that matters.

  • ncdu, friend of htop and a nice disk usage display for the terminal.

  • aristocratos/bpytop: Linux/OSX/FreeBSD resource monitor

  • duf a better df

  • dust: “du on steroids.”

  • duc, also a nice drive-use visualizer.

  • dalance/procs: A modern replacement for ps written in Rust

  • aristocratos/bpytop: Linux/OSX/FreeBSD resource monitor

  • Tree: show you the tree structure of directories, a bit like microdosing on Midnight Commander from back in the day.

  • Not really a new thing but a quality of life improvement: the “ducks” alias., “ducks: linux command for the 10 largest files in current directory”

3 Nice prompts

Try Starship: Cross-Shell Prompt.

4 Who owns this PID?

ps -o user -p $PID

5 WTF ^M?

Return produces ^M instead of a newline? Try:

stty sane^J

or possibly

stty icrn^J

For other miscellaneous screen garbage, maybe reset will help?

reset

It is more complicated if I made a mess in tmux.

As far as I am concerned this is all dark magic. If this nonsense wastes 2 hours of my life in total it will not justify the rather lengthier process of getting a better mental model of how terminals work.

6 File system watching

In Watch That Filesystem, Al Williams discusses how to trigger things based on filesystem events via inotifywait and incron.

Thanks Yohans Bastian for pointing out this handy trick to find the PID of the process using the inotify watchers.

find /proc/*/fd \
    -lname anon_inode:inotify \
    -printf '%hinfo/%f\n' 2>/dev/null \
    | xargs grep -c '^inotify' \
    | sort -n -t: -k2 -r

Cross platform filewatcher: emcrisostomo/fswatch:

A cross-platform file change monitor with multiple backends: Apple OS X File System Events, *BSD kqueue, Solaris/Illumos File Events Notification, Linux inotify, Microsoft Windows and a stat()-based backend.

7 Awk

pement.org awk one-liners

8 rebuild on change

entr watches for changed files and recompiles your whatsit when it gets edited. This is incredibly useful for automating life.

9 Which file is crashing/hanging $PID?

lsof -r -p $PID | grep /path/to/file

10 Vars, expansions, file names, white space hell

See bash or fish depending on choice of shell.

Or avoid both by using some other utility, such as…

11 rename

rename is a script that makes renaming work how I imagine it should, avoiding the mysterious punctuation stew at least somewhat.

rename -s html txt *.html

NB depending on distro you may get some other systutil rename which is much less powerful than the one I linked to, albeit still often powerful enough.

12 Text processing

12.1 Trailing whitespace

A shell script to remove trailing whitespace from a file - put this in trimspace.sh:

#!/bin/bash

# macOS version
sed -i '' -e’s/[[:space:]]*$//' "$1"
#!/bin/bash

# GNU version
sed -i -e’s/[ \t]*$//' "$1"

Then you can trim trailing whitespace from your… whatever… by putting this line in there:

find . -type f -print0 | xargs -0 -I {} trimspace.sh \{\}

12.2 Data wrangling

See text data processing.

13 Incoming

13.1 rsync files in random order

based of Ole Tange’s tor version

Remotely

find . -maxdepth 4 -depth -type d | shuf | rsync --delete -zHax --inplace --rsync-path='mkdir -p {} && rsync' ~/{}/ remote.host:/some/dir/{}/

Presumably this works locally:

for file in (find . -maxdepth 4 -depth -type d | shuf)
  mkdir -p "$file" && rsync --delete -Hax --inplace - ./{}/ /some/dir/{}/
end

13.2 Download from command line without getting owned

Default curl is insecure.

curl --tlsv1.2 --proto=https --location \
  --remote-name-all --remote-header-name

13.3 Find common diacritics in filenames

Caught in unicode crossfire? Try

find . -iname "*[üñàáèéöäçã]*"

14 Which process is bound to port $PORT?

This one!

lsof -nP -i4TCP:$PORT | grep LISTEN

14.1 Sync only if drive present

test -d /Volumes/syncdrive/ && rsync --delete -avz \
    192.168.0.1:/path/to/stuff/ /Volumes/syncdrive/

14.2 Unzip zips into subdir using fish

for foo in *.zip
    unzip $foo -d (basename $foo .zip)
end

14.3 Set operations

comm.

15 Meta command lines

Command lines to command your command lines.

I suppose if I were a good person I’d check if any of the above commands are novel and submit them to tldr or version my .cheats folder in a dotfile repo, or mention them in commandlinefu but I’m now exhausted and just want to go home.

15.1 Fig

Fig is a command line autocompleter and syncer and secret manager which focuses on enabling teams with sahred shortcuts and utilities.

15.2 Explainshell

Explainshell dissects a shell command and shows you the documentation for each part of it. Good for instilling this knowledge in your brain.

15.3 tldr

tldr:

New to the command-line world? Or just a little rusty? Or perhaps you can’t always remember the arguments to lsof, or tar?

…And the manual for your typical command is utterly incomprehensible, so remembering is obviously preferable to trying to decipher it.

First

## install
npm install -g tldr
# or
brew install tldr
# invoke
tldr tar

Alternative implementation:

## install
brew install tealdeer
# invoke is still
tldr tar

15.4 cheat

cheat

…allows you to create and view interactive cheatsheets on the command-line. It was designed to help remind *nix system administrators of options for commands that they use frequently, but not frequently enough to remember.

## install
pip install cheat
# or
brew install cheat
# invoke
cheat tar

15.5 how do i

howdoi:

Are you a hack programmer? Do you find yourself constantly Googling for how to do basic programming tasks?

Suppose you want to know how to format a date in bash. Why open your browser and read through blogs (risking major distraction) when you can simply stay in the console and ask howdoi

pip install howdoi
howdoi tar

Seems to search the internet for you, and not be command-line specific, which is broader in scope than some of the other entrants here, but also noisier.

15.6 commandlinefu

commandlinefu has an awful command-line interface, but the website is so good that it makes the grade.

15.7 bash hackers wiki

bash hackers wiki: avoid its the paradigmatically awful bash manual

16 Parallel execution