Unix tool tip

'The enjoyment of one's tools is an essential ingredient of successful work.' -- Donald E. Knuth

A sed command can have no address, one address, or a pair of addresses separated by a comma.

Randomly sample a file from the shell johndcook.com/blog/2019/05/2…

Hexadecimal dump of a file: od -x <file>

As an address in sed, $ is the line number of the last line in a file.

Current UTC time: date -u

Emacs and Vim in the Age of AI batsov.com/articles/2026/…

For daily tips on regular expressions, follow @RegexTip.

diff -e produces an ed program. ed is the ancestor of sed.

find, grep, sed, and awk wilsonericn.wordpress.com/2011/08/25/fin…

Programs with verbose start-up messages interrupt your workflow at the command line. How to fix that: johndcook.com/blog/2019/09/0…

Addresses in sed specify which lines to act on. They can be line numbers or regular expressions.

In awk, records are split into fields by a separator. By default fields are separated by white space.

View a CSV file in Emacs, aligning columns: M-x csv-align-fields

incredible that we built all this RAG and vector database stuff and it turns out that grep from 1973 works better than all that

How to use bc's six basic math functions to compute everything else johndcook.com/blog/2021/01/0…

How to undo almost anything with git github.com/blog/2019-how-…

In Emacs, list lines matching a regular expression: M-x occur

New post: ~- johndcook.com/blog/2026/03/0…

New post: Working with file extensions in bash scripts johndcook.com/blog/2026/02/2…

Sort a file based on the 3rd field in each line: sort -k 3. Fields separated by white space by default. Change the default with -t.