echo, cat: add stdin example

[Managor]

Checklist

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR contains at most 5 new pages.
• The PR is authored by me, or has been human-reviewed if it was created with AI or machine translation software.
• The PR title conforms to the recommended templates.
• Version of the command being documented (if known):

Reference issue: #

[dmmqz]

I think using "command" instead of "program" would be more consistent with other pages.

[Managor]

$ grep -r "{{command}}" | wc -l
528
$ grep -r "{{program}}" | wc -l
39

However I sort of agree that in this case program makes more sense. You're essentially passing the data to the program while the command is just the syntax for the program. Does anyone have any differing opinions?

[kbdharun]

$ grep -r "{{command}}" | wc -l
528
$ grep -r "{{program}}" | wc -l
39

However I sort of agree that in this case program makes more sense. You're essentially passing the data to the program while the command is just the syntax for the program. Does anyone have any differing opinions?

I think both would work fine here in English, but translating command is easier/more direct than program in most languages, since "program" might mean a computer program or an event. But in case of command it just has a singular meaning.

[tldr-bot]

The build for this PR failed with the following error(s) at commit
bdc1311e90d6a50bcbd06972594aded05c833e6c:

pages/linux/cat.md:32:36 MD047/single-trailing-newline Files should end with a single newline character
pages/linux/cat.md:1: TLDR009 Page should contain a newline at end of file

Please fix the error(s) and push again.