05 Searching and Finding

Learning objectives

• Find files by name, type, and time.
• Search for keywords in file content.
• Locate the path of a command program.

Command overview

Command	Purpose	Meaning	Basic usage	Example
find	Find files and directories	Recursively finds paths under a specified directory	find path conditions	find . -name "*.log"
grep	Search text content	Matches text in a file or input stream	grep [options] pattern file	grep "error" app.log
command -v	Inspect command resolution	POSIX Shell query for how a command name resolves	command -v name	command -v python3
type -a	Inspect a Bash command source	Shows aliases, functions, builtins, and multiple file locations	type -a name	type -a python3
which	Legacy path-query tool	Implementations vary and can omit aliases/functions/builtins	which name	which python3
whereis	Find command-related files	Finds binary, source, and manual locations	whereis command	whereis bash
locate	Find files quickly	Finds paths using a system index	locate keyword	locate nginx.conf

Common scenarios

Find files by name:

find . -name "*.log"
find ./logs -type f -name "*.log"

Find recently changed files:

find . -type f -mtime -7

Search file content:

grep "error" app.log
grep -r "deprecated_flag" ./src
grep -n "failed" app.log

Locate a command:

command -v -- python3
type -a -- python3
whereis bash

Notes for beginners

• find . starts at the current directory.
• find / scans the entire system. It can be slow, cross mount points, and collect irrelevant paths; practice only in a lab directory.
• grep -r recursively searches a directory and is useful for finding a keyword in a project.
• grep -n shows line numbers for easier location.
• locate depends on an index, so it may not find a newly created file; find is more reliable in that situation.
• find -mtime -7 uses rounded 24-hour periods, not the preceding seven calendar days.
• Use grep -F for literal text and grep -E or default BRE for regular expressions. In a regular expression, . matches any single character.

Safe filenames and restricted scope

When passing find results to another command, prefer -exec ... {} +:

find ./logs -type f -name '*.log' -exec wc -l -- {} +

It does not split legal file names on newlines. GNU/Linux also supports -print0 | xargs -0; see Text processing.

Exercise

In a lab directory, create three .log files and one log whose name contains a space. Complete four kinds of query: name, modification time, fixed string, and regular expression. For acceptance, record the starting path, hit count, and exit status; do not scan / or a real /var/log.

References

• GNU Findutils
• GNU grep
• POSIX command