Exercise

Line Anchors Exercise

Task

In this hands-on exercise, anchor patterns to the start or end of a line, then use those positions to filter a directory listing.

Target host: servera
Privileges: sudo access to install the words package

Install the dictionary and search without anchors

The file /usr/share/dict/words comes from the words package, which is not installed by default.
```
ssh student@servera
sudo dnf install -y words
ls -l /usr/share/dict/words
```
Search the dictionary for a short word and note how many unrelated results appear, such as bobcat and duplicate.
```
grep 'cat' /usr/share/dict/words
```
Compare start, end, and exact-line anchors

Add ^ to require that the match start at the beginning of the line.
```
grep '^cat' /usr/share/dict/words
```
Add $ instead, to require that the match run to the end of the line.
```
grep 'cat$' /usr/share/dict/words
```
With both anchors the line must contain exactly this word and nothing else.
```
grep '^cat$' /usr/share/dict/words
```
A useful consequence The pattern ^$ matches a line whose beginning is immediately followed by its end — a blank line. Combine it with -v to strip blank lines out of a configuration file.
Use a start anchor to identify directories

The first character of each line of ls -l output is the file type. Without an anchor, searching for d matches almost every line.
```
ls -l /etc | grep 'd'
```
Anchored to the beginning of the line, it returns only directories.
```
ls -l /etc | grep '^d'
```
Use an end anchor to identify configuration files

A dot is a wildcard to grep, so escape it with a backslash to match a literal period.
```
ls -l /etc | grep '\.conf$'
```
Two layers of interpretation The single quotes stop Bash from acting on the backslash, so grep receives \. intact and treats it as a literal dot.

Task

Install the dictionary and search without anchors

Compare start, end, and exact-line anchors

Use a start anchor to identify directories

Use an end anchor to identify configuration files