on ubuntu terminal, how to remove all the spaces from all the file names in a directory?

$ rename 's/ /_/g' *

How to delete all the lines which contain a pattern in vim?

https://vim.fandom.com/wiki/Delete_all_lines_containing_a_pattern

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The ex command g is very useful for acting on lines that match a pattern. You can use it with the d command, to delete all lines that contain a particular pattern, or all lines that do not contain a pattern.

For example, to delete all lines containing "profile" (remove the /d to show the lines that the command will delete):

:g/profile/d

More complex patterns can be used, such as deleting all lines that are empty or that contain only whitespace:

:g/^\s*$/d

To delete all lines that do not contain a pattern, use g!, like this command to delete all lines that are not comment lines in a Vim script:

:g!/^\s*"/d

Note that g! is equivalent to v, so you could also do the above with:

:v/^\s*"/d

The next example shows use of \| ("or") to delete all lines except those that contain "error" or "warn" or "fail" (:help pattern):

:v/error\|warn\|fail/d

How to create an alias command in git to display a log in graph?

How to create an alias command in git to display a log in graph?

$alias graph="git log --all --oneline --graph  --decorate"

(I find that it outputs the same as without '--decorate'.)

Note:

'--oneline' is a shorthand for both '--pretty=oneline' and  '--abbrev-commit' used together.

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I find the 2 following commands are very helpful,

1.

$git log --all --oneline --graph

2.

$git show-branch --all --more=1000

(you can replace 1000 with any number, according to your requirements.)