Context Lines

Context lines help you understand why a match occurred — the code or log data before and after.

The Three Flags

Flag	Meaning
-A N	N lines after the match
-B N	N lines before the match
-C N	N lines both sides

Practical Examples

# See a function signature and its first 15 lines of body
ag -A 15 "def process_payment" src/

# See 5 lines before a crash line (state leading up to it)
ag -B 5 "Segmentation fault" syslog

# Full context for debugging an auth error
ag -C 4 "authentication failed" /var/log/auth.log

Stack Trace Capture

Capture a full Java stack trace (exception + 30 following lines):

ag -A 30 "java.lang.NullPointerException" application.log

Then count unique exception types:

ag -o "java\.lang\.\w+Exception" application.log | sort | uniq -c | sort -nr

Context Separator

Between non-adjacent match groups, ag inserts -- as a visual separator:

app.log
42-  connecting to db
43:  ERROR: timeout           ← match
44-  retrying...
--
102:  ERROR: auth failed      ← match
103-  account locked

Suppress the separator for scripting:

ag --no-group-separator -C 2 "ERROR" app.log | process.sh