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First steps / Stage 12 of 15

Pipelines: an answer from several commands

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Step 7 of 7 · summary · 2 min

Summary

  • | passes stream 1 of the command on the left to the standard input of the command on the right; a filter given no file name reads that input.
  • Repeats in a column are counted with cut … | sort | uniq -c: uniq glues together only neighbouring lines, so sort goes before it.
  • sort -rn | head -n 3 keeps the three most frequent lines. A long pipeline is built one link at a time, checking the output through head.
  • The colleague's command at the start of the lesson has five links: the addresses, sorting, counting, ordering from high to low and the top three lines.

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Reference for this lesson

Articles

  • Output redirection and pipelines — A shell instruction that connects a command's stream to a file or another descriptor: > overwrites a file, >> appends, < reads from a file, and 2>&1 sends stderr wherever stdout goes.
  • head — the first lines of a file — The head command prints the beginning of a file or of command output — 10 lines by default, -n sets how many.
  • grep — searching text — The grep command finds lines matching a pattern in files and command output: regex, recursion, context.
  • wc — count lines, words and bytes — The wc command counts lines (-l), words (-w), bytes (-c) and characters (-m) in a file or in command output.
  • sort — sort lines — The sort command orders lines of a file or command output: as text, as numbers (-n), by field (-k), reversed (-r).
  • uniq — remove or count repeated lines — The uniq command collapses adjacent identical lines and counts them with -c; sort almost always comes before it.
  • cut — cut fields out of lines — The cut command takes fields out of every line by a delimiter (-d and -f) or characters by position (-c).
Ubuntu 24.04
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