linux · medium

Text Processing — grep, awk, sed, pipes & xargs

Command-line text processing: grep (-r/-I/-n/-o/-c), pipes and the 2>&1 ordering trap, awk for column aggregation, sed -i for substitution, and the universal sort | uniq -c | sort -rn count-and-rank pipeline.

🔑 Key line

grep -rIn / -o / -c to search. Streams: > truncate, >> append, 2>&1 (after >) merges stderr. awk for columns ({sum+=$N} END), sed -i for substitution. Universal idiom: sort | uniq -c | sort -rn = count & rank.

The code

grep -rIn 'error' /var/log/   # recursive, line nums, skip binaries
grep -oE 'feed:[0-9]+' f      # print only the match

cmd > out 2>&1                # stdout + stderr to a file

awk '{sum+=$10} END{print sum}' f   # sum a column
sed -i 's/old/new/g' f              # in-place substitute

# The universal count-and-rank pipeline
awk '{print $1}' f | sort | uniq -c | sort -rn | head

What this lesson walks through

01grep: find lines fast
02Pipes & the 2>&1 order trap
03The count-and-rank pipeline

grep -rIn searches recursively with line numbers; -o extracts just the match, -c counts, -v inverts.

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