Finding Files and Folders

Objectives

By the end of this chapter, you should be able to:

Compare and contrast find and grep
Use find to search for files and folders, including wildcards
Use grep flags to search text more precisely
Explain what a regular expression is, at a basic level

💡 Why this matters: find and grep are two of the most-used commands in any developer’s day — being fluent with them means never opening Spotlight, Alfred, or a GUI search box again.

Finding Files with `find`

find locates files and folders without any GUI search tool. The simplest form is find plus a name, searching from your current location:

bash

find Downloads

Run from your home directory, that lists everything inside Downloads. (Point find at a folder rather than a file, and you get everything inside it too.)

For more control, find takes a path and an expression:

bash

find . -name "first.txt"

That searches the current directory (.) for anything named exactly first.txt.

Wildcards with `find`

Three wildcard characters make find far more flexible:

* — any number of characters
? — exactly one character
[] — any one of the characters listed inside the brackets

A few examples, assuming you’re searching the current folder:

Anything ending in .html: find . -name "*.html"
Anything with a three-letter extension, like .txt or .css: find . -name "*.???"
Anything starting with f, t, or s: find . -name "[fts]*"
Anything with main anywhere in the name: find . -name "*main*"

Searching Text with `grep`

Where find locates files and folders, grep searches inside text — you already used it piped after cat in the last module. Given a file names.txt containing:

text

Lisa
Mark
Erin
Beth
Tim
Elizabeth
Tom
Matt
Liza
Janey
Jane
Shana

a handful of flags make grep much more precise:

Flag	Does	Example
`-i`	Case-insensitive match	`grep -i "erin" names.txt` → `Erin`
`-w`	Match whole words only	`grep -iw "beth" names.txt` matches only `Beth`, not `Elizabeth`
`-A N`	Show `N` lines after a match	`grep -A 3 "Beth" names.txt`
`-B N`	Show `N` lines before a match	`grep -B 3 "Beth" names.txt`
`-C N`	Show `N` lines around a match	`grep -C 3 "Beth" names.txt`
`-v`	Invert — show non-matching lines	`grep -v "Jane" names.txt`
`-c`	Count matches	`grep -c "Jane" names.txt` → `2`
`-n`	Show line numbers	`grep -ni "Jane" names.txt` → `10:Janey`, `11:Jane`

There are more flags than this — man grep has the full list.

Regular Expressions

Wildcards work with find, but searching text for a pattern instead of an exact word uses regular expressions — a syntax for describing patterns in a string, powerful enough to validate an email address or phone number format. A full treatment is its own topic, but a few building blocks go a long way:

. matches any single character. How many names are exactly four characters long? grep -wc "...." names.txt → 7
* matches zero or more of whatever precedes it. How many names start with a capital T? grep -wc "T.*" names.txt → 2
[] matches any one listed character. How many names start with L, M, or E? grep -wc "[LME].*" names.txt → 6
[^] negates — matches anything not listed. How many names don’t start with T? grep -wc "[^T].*" names.txt → 10

Try It

Both commands search your real filesystem and real files, so try these yourself:

Pick a folder with a few files in it and use find with a wildcard to locate everything of one file extension.
Recreate the names.txt file above and confirm the grep -wc counts for yourself.
Use -A, -B, or -C to print a few lines of context around a match in any text file you have handy.

Recap

find locates files and folders, optionally using *, ?, and [] wildcards.
grep searches inside text, and flags like -i, -w, -c, and -n narrow that search down.
Regular expressions (., *, [], [^]) describe patterns rather than exact text, and work with grep far beyond what wildcards alone can do.

Next up: a set of exercises pulling together environment variables, processes, find, and grep.