Text and search

A regular expression is a pattern that many strings match; grep searches by it, sed replaces by it, awk selects lines.

The cat command prints a file's contents to the terminal and joins several files into one stream.

The less pager shows a long file or command output screen by screen — scroll, search by word, follow the end.

The head command prints the beginning of a file or of command output — 10 lines by default, -n sets how many.

The tail command prints the end of a file, and with -f it keeps showing new lines as they are appended to a log.

Splits a stream: writes to a file AND shows it on screen; sudo tee to write into protected files.

The grep command finds lines matching a pattern in files and command output: regex, recursion, context.

The wc command counts lines (-l), words (-w), bytes (-c) and characters (-m) in a file or in command output.

The sort command orders lines of a file or command output: as text, as numbers (-n), by field (-k), reversed (-r).

The uniq command collapses adjacent identical lines and counts them with -c; sort almost always comes before it.

The cut command takes fields out of every line by a delimiter (-d and -f) or characters by position (-c).

sed edits and deletes lines by pattern, awk splits lines into fields and computes over them, line by line.

Small pipeline utilities; uniq only removes adjacent duplicates, so it almost always needs sort before it.

Comparing files and applying patches: diff two configs, see what changed, apply a patch.

Parsing and filtering JSON on the command line — fields, arrays, filters, formatting.

A Bash builtin for inspecting and clearing remembered paths to external commands.