Redirection in a command changes the output format

spark_sara

I needed the command wc -l [file] to display only the number of lines. On a forum somewhere on the Internet, a very helpful user answered exactly this same question. Unfortunately, he didn’t explain why it worked. I’ll use one of my files from the /home/user/ directory as an example: ~$ wc -l f2; echo $(0< f2 wc -l); echo $(< f2 wc -l) 559 f2 559 559 I just don't understand why redirecting the contents of the f2 file to standard input can change...

Originally asked by mazda on Stack Exchange (superuser) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

In the second and third commands, wc -l reads content from the standard input and counts the number of lines it received. It has no knowledge that the standard input had the content of f2 written to it. Since there's no file here, you just get the number of lines, without the file name.

Full answer by Mureinik: https://superuser.stackexchange.com/a/1940750 (CC BY-SA 4.0).

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