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Searching

You can create and view files. Now let's learn how to find them, search inside them, and filter output.

Finding vs Searching

Before diving in, understand the difference between the two main tools:

Tool What it looks for Best used for
find File metadata (Names, dates, sizes) Locating a lost file or directory
grep Text content inside files Finding a specific line, variable, or log error

find - Search for files and directories

The find command searches the filesystem based on names, size, permissions, and even time.

find . -name "notes.txt"   # find "notes.txt" in current directory and subfolders

Useful options

Option What it does Example
-name Search by filename (case-sensitive) find . -name "app.log"
-iname Search by filename (case-insensitive) find . -iname "readme.md"
-type f Search for files only find . -type f
-type d Search for directories only find . -type d -name "src"
-maxdepth Limit how deep subfolders are searched find . -maxdepth 1 -name "*.sh"

Pros: Extremely powerful filtering. Cons: Syntax can be tricky for complex searches.

Searching by Time (Advanced)

You can locate files based on when they were last modified or accessed.

  • -mmin N: Content was modified N minutes ago.
  • -mtime N: Content was modified N days ago.
find . -mmin -60          # Modified in the last hour (less than 60 mins)
find . -mtime -7          # Modified in the last 7 days
find . -mtime +3 -mtime -7 # Modified between 3 and 7 days ago

Permissions and Ownership

sudo find /srv -user ryan    # Files owned by user "ryan"
find . -perm 777             # Files with unsafe world-writable permissions

grep - Search for text inside files

Instead of digging through countless lines manually, grep scans the content of files to match text patterns.

grep "error" log.txt   # prints lines containing "error"

Common Grep Flags

Option What it does Example
-i Ignore case (case-insensitive) grep -i "critical" app.log
-r Search recursively in subfolders grep -r "TODO" ./projects
-n Show line numbers of the match grep -n "main" script.py
-v Invert match (hide lines matching text) grep -v "info" debug.log
-c Count the number of matching lines grep -c "fox" sample.txt
-e Protect patterns starting with a hyphen - grep -e "-v" file.conf

Tip

Use grep -e "pattern" or grep -- "pattern" when your search text starts with -. This prevents grep from treating the search string as an option.

| (Pipe) - Combine commands to filter output

Just like in Redirection, the pipe | takes the stdout of the left command and passes it as stdin to grep. This lets you search live terminal outputs.

history | grep "sudo"  # search your command history for "sudo"

ls -la | grep "Dec"    # show only files modified in December
ps aux | grep "python" # search active system processes for "python"

Advanced Filtering with Regex

Using $ anchors your search to the end of a line:

ls /var/log | grep '.log$'  # list only files ending exactly with .log

Danger

Avoid parsing ls output in scripts. This is only a reliable technique for interactive filtering.

You can chain multiple pipes together: history | grep "git" | grep -v "commit"

Command Options What it does
find -name -iname Search by filename (case-sensitive / case-insensitive)
find -type f / -type d Filter results by files or directories
find -maxdepth N Limit how deep subfolders are searched
find -mmin -N / -mtime -N Find files modified in the last N minutes/days
find -perm [mode] Search for files with specific permissions
grep -i -r Ignore case / search recursively in subfolders
grep -n -v Show matching line numbers / Hide matching lines
grep -c -e Count matches / Protect patterns starting with -
| - Send command output into grep for filtering

Note: Use grep -- pattern or grep -e pattern when the search text starts with -.

Check Your Understanding

Test yourself with these real terminal scenarios.

1. Save a directory listing

You edited a configuration file 5 minutes ago but forgot which one it was in a sea of folders.

What command shows files modified in the last 10 minutes?

Reveal Answer 
find . -mmin -10

You need to find where a specific environment variable named STRIPE_SECRET is defined inside a large multi-folder project. You need to know the exact file and line number.

What command do you type?

Reveal Answer 
grep -rn "STRIPE_SECRET" .

3. Hyphen Pattern Traps

You want to search a configuration file named settings.json for the exact string --debug.

What command ensures the pattern isn't confused with a flag?

Reveal Answer 
grep -e "--debug" settings.json

4. Live Server Stats

Instead of seeing hundreds of log lines containing the word "404", you just want a quick count of how many times a "404" error occurred in access.log.

What command do you run?

Reveal Answer 
grep -c "404" access.log

5. Advanced Pipe Filtering

You are listing a directory using ls /var/log, but you only want to see filenames that end precisely with .log.

How do you filter the output using a pipe and regex?

Reveal Answer 
ls /var/log | grep '.log$'