Command Line Tricks

A collection of useful command line tricks

Create File with Content

To create a file including content (overwriting the file if it exists), use echo with the -e flag (to allow for escape sequences like the \n newline) and redirect to a file with >:

echo -e 'abc\ndef' > 1.txt

Now 1.txt will include the following content:

abc
def

To make multi-line content more readable, use cat with a heredoc tag like EOF:

cat << EOF > main.ts
import { add } from './add.js';

console.log(add(2,3));
EOF

FFmpeg: Combine two video files

Combine two video files using FFmpeg

ls video1.mp4 video2.mp4 | while read line; do echo file \'$line\'; done | ffmpeg -protocol_whitelist file,pipe -f concat -i - -c copy output.mp4

Source: How to concatenate two MP4 files using FFmpeg? (Answer) | Stack Overflow

Find and Replace in Git Remote

Sometimes you may want to search and replace within your Git remote - for example, if you change your username on GitHub. This is a command to do it (replaces OldUsername with NewUsername):

git remote set-url origin $(current_origin=$(git remote get-url origin --push) && echo ${current_origin/OldUsername/NewUsername})

gzip web assets

Loop over CSS, JS, EOT, SVG and TTF files and gzip them into a folder named gzipped.

gzip-web-assets.sh

#!/usr/bin/env bash

# Usage:
# $ ./gzip-web-assets.sh

mkdir gzipped
for file in $(find . -type f -depth 1 | egrep "\.(css|js|eot|svg|ttf)$") ; do
  gzip -c --best $file > gzipped/$file
done

Set zsh custom tab title

To set a custom terminal tab title with zsh, configure the zsh precmd and preexec hook functions in .zshrc:

~/.zshrc

# Disable auto-setting terminal title.
DISABLE_AUTO_TITLE="true"
function precmd () {
  echo -ne "\033]0;Custom title: $(print -rD $PWD)\007"
}
precmd

function preexec () {
  print -Pn "\e]0;🚀 $(print -rD $PWD) $1 🚀\a"
}

This will change the tab title as such:

1. Show the Custom title: prefix before the present working directory
2. When a foreground program is running, rocket emojis will appear at the beginning and end of the prompt to show a visual indicator that something is running

Screen.Recording.2025-02-15.at.17.36.47.mov

To use this with Ghostty, disable Ghostty's built-in shell integration using shell-integration-features = no-title:

~/Library/Application Support/com.mitchellh.ghostty/config

# Disable Ghostty built-in tab title shell integration
# https://ghostty.org/docs/config/reference#shell-integration-features
shell-integration-features = no-title

Wrap command and exit based on stdout

To wrap a command and exit based on stdout from the command, loop over each line of the stdout to look for the message. If the message is found, set a variable to true and exit with code 1:

pnpm install | { has_ignored_build_scripts=false; while IFS= read -r line; do echo "$line"; [[ "$line" == *"Ignored build scripts:"* ]] && has_ignored_build_scripts=true; done; [[ "$has_ignored_build_scripts" = false ]]; }

Source: Fail pnpm install on pnpm v10 ignored build scripts