指令裡面的dash - 代表標準輸入

在指令裡面，dash (-, 通常是按鍵0右邊那個)代表的是標準輸入(standard input)：

1. cat ERR194147.fastq.gz | pv | time seqtk fqchk -q 30 - 
2. zcat ERR194147.fastq.gz | pv | time seqtk fqchk -q 30 -
3. unpigz -p 4 -c ERR194147.fastq.gz | pv | time seqtk fqchk -q 30 -

上述三個指令都是等價的，seqtk後面原本是應該要加入一個檔案的。這時用 -，代表seqtk要讀取的檔案是從標準輸入來，然後這個標準輸入又會是前一個pipe的輸出

相關資料

• 14 Useful “cat” Command Examples in Linux
• Pipes, Forks, & Dups: Understanding Command Execution and Input/Output Data Flow：用很漂亮的圖解釋pipe, fork

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