Useful bash commands I always forget...

A mixed bunch of bash commands that I keep coming back to.

Warning: I’ve mostly used these on Mac OS X, not Linux.

One > overwrites, two >> appends

cat hello.txt >> world.txt

I almost always want >> but never remember which is which.

Find the total disk usage of a directory

du -hcs dirname

The option h is for human-readable, c is the total count and s gives a summary (as opposed to a breakdown). More…

Check a file’s MIME type

file --mime-type -b filename

The -b is for ‘brief’ and omits the filename from the output line.

Using find to execute a command on each matching file

find . -type f -name '*.txt' -exec sed -i '.bak' s/this/that/ {} +

Let’s break this one down. We want to find…

  • in the current directory . (or this could/be/any/path)
  • something that has a -type of f for file
  • whose -name mathches this regular expression '*.txt'
  • then -execute this following command for every file:
  • sed replace text in the file, and do this -in place
  • but before you do, make a backup with extension '.bak'
  • we want to replace s/this/that (the word ‘this’ for the word ‘that’)
  • for each find result that is passed into sed in place of the curly braces {}
  • and lastly, the + at the end means find will pass all matching file names to the exec command at once (this is a bit confusing but this Stack Overflow answer helped)

My most-used grep command

By force of habit, I still prefer grep to other text search tools 🤓

grep -rli --exclude-dir=libs "videoPlayer" app/js

Nothing crazy here. -r will recursively search directories, -i is case-insensitive and -l will not output matching lines (just the filename). Sometimes it’s useful to --exclude-directories (e.g. node_modules)

Grepping your command history

history | grep test.txt

history will list your most recent terminal commands. Piping | this to grep will filter those commands that match, in this case that contain test.txt.

Matching commands will be preceded by an ID number like 509 touch test.txt and you can run this command again by typing an exclamation mark followed by the ID, in this case !509.

This can be handy for those long, cryptic commands that you need to go back to.

Find any processes listening to a specific port (and kill them if needed)

sudo lsof -i :8080 | grep LISTEN
ps -ef 3447
kill -9 3447

lsof is short for ‘list open files’, where ‘files’ includes network files or sockets. In this case we filter by port :8080 and pipe the result to grep so that only the files that are LISTENing will be listed.

The process status ps gives us more info about the process with id 3447. The -e flag selects all processes and -f outputs full listing details.

The last command kills the process with that id. The -9 flag prevents the process from resisting so only use this if you’re sure you want to kill it.

Written on April 27, 2015