Sed simple use (iii) Replace

SED usage record. Text substitution

0. test file content

1. Remove leading whitespace characters

2. Delete trailing whitespace characters

I don't see the effect.

3. Remove leading and trailing whitespace characters

Trailing delete or not see the effect

4. Insert 5 spaces at each line of the switch

5. Align text to the right by 79 character widths

It doesn't appear to be right-aligned because there are spaces or tabs behind it.

6. Center the contents of the file, with a width of 79 characters

7. Find the character and replace the found string with the specified string

A. Replace only the first matching string in each row

B. Replace only the second matched string in each row

C. Replacing all matching strings in each row

D. Replacing the second-to-last match

E. Replacing the last occurrence

8. Processing only in rows where a particular string appears

A. Replacing a string

B. Not appearing when a specific string is replaced

9. Multiple matching replacements

Replace ":/", ":", "/" with "="

Sed simple use (iii) Replace