Pinned: stuffs that I keep googling again and again and again...

because my memory won't last longer than 7 seconds.


FOLDED, click entry to expand

linux general

unix - file permissions
NUMBER   PERM
--------------
1       x
2       w
4       r

7       rwx
6       rw-
5       r-x
4       r--
bash - check number of command line parameters
if [ ! $# -eq 1 ]; then
	echo "usage: $0 -h blah blah" >&2
	exit 1
fi
tools - creating / extracting archives
extension   create                  extract                 notes
-------------------------------------------------------------------------------
.tar.gz     tar -czvf a.tar.gz a/   tar -xzvf a.tar.gz      z:gz j:gz2
-------------------------------------------------------------------------------
.tar        tar -cvf  a.tar a/      tar -xvf a.tar
-------------------------------------------------------------------------------
.gz         gzip -c file > a.gz     gzip -dk a.gz           use -r for dir/
-------------------------------------------------------------------------------
.zip        zip file1 file2 ...     unzip a.zip             use -r for dir/
-------------------------------------------------------------------------------
tools - grep and find
# grep string pattern from directory

$ grep -ril <pattern> <dir>
    -r recursive
    -i ignore casing
    -l show the matched line (otherwise only filename)

# find by name
$ find <path> -name <pattern>

# find by type
$ find <path> -type f       # find file
              -type d       # find directory
              -executable   # find executable
              -perm +/-xyz  # w/o permission code xyz

git / version control

git - Checking out a git(hub) PR locally
git fetch origin pull/ID/head:BRANCH_NAME
git - Delete the last commit but keep the changes
git reset HEAD^
git - Checkout (reset) a file to a specific commit
git checkout <HASH> -- file1/to/restore file2/to/restore
git - send-email
git send-email --to="rec@email" [REF]

[REF]
    e.g. HEAD~ , HEAD^2, <commit id>

[EMAIL OPTS]
    -v<n> patch version (in the subject)
    --subject-prefix=<str> e.g. "PATCH v4"
    -l<n> log e.g. -l4 (changes since v1 etc..)
    --cc/--bcc=<addr>
    --from=<addr>
    --reply-to=<addr>
    --compose: invoke editor
    --reply-to=<addr>
    --in-reply-to=<id>
    --subject=<str>
    --to option, among others can be specified multiple times

Sourcehut’s tutorial is a great starting point

git am
git am [mbox]

# For sr.ht lists:
curl -s https://lists.sr.ht/~shrik3/test_list/patches/47533/mbox | git am -3

# For mutt: directly pipe mail content to git am

`| git am`

Sourcehut’s tutorial is a great starting point

keybase

gpg - select subkey to use
gpg -u SUBKEYID! --sign ....

# the ! after keyid is important!

--local-user name
-u     Use name as the key to sign with. Note that this option overrides --default-key.

When using gpg an exclamation mark (!) may be appended to force using the specified primary or secondary key and not to try and calculate which primary or secondary key to use.

Also refer to man gpg HOW TO SPECIFY A USER ID

Sourcehut’s tutorial is a great starting point

programming

Makefile - magic variables
out.o: src.c src.h
  $@   # "out.o" (target)
  $<   # "src.c" (first prerequisite)
  $^   # "src.c src.h" (all prerequisites)

%.o: %.c
  $*   # the 'stem' with which an implicit rule matches ("foo" in "foo.c")

also:
  $+   # prerequisites (all, with duplication)
  $?   # prerequisites (new ones)
  $|   # prerequisites (order-only?)

  $(@D) # target directory
Makefile - commands and functions
c_source  := $(wildcard src/*.c)  
all_files := $(shell find images -name "*")

# substitutions
  file     = $(SOURCE: .c=.o)    # .cpp => .o
  list     = $(patsubst %.c, %.o, $(wildcard *.c))

  -   # ignore errors
  @   # dont print command
  +   # run even in 'don't execute' mode

archlinux

pacman - frequently used commands
-Sc         : clear cache
-Qqe        : list explicitly installed packages
-Ql         : show file list of a package
-F <file>   : show which package a file belongs to
-Si         : extensive information
-Qi         : ^ for locally installed packages
-Qii        : ^ also with list of backup files 

# clean orphans
$ pacman -Qtdq | sudo pacman -Rns -

# install package from PKGBUILD
$ makepkg -si
packaging - PKGBUILD
# guidelines : https://wiki.archlinux.org/title/Category:Arch_package_guidelines
# Prototypes : /usr/share/pacman/

# Very basic example:

pkgname=myprog
pkgver=1.2.3
pkgrel=1
pkgdesc='this is a program'
arch=('x86_64' 'arm')
url="https://git.vnil.de/repo.git/"
license=('GPL3')
depends=('libretls' 'ncurses')
source=("https://git.vnil.de/${pkgname}.git/whatever_path/${pkgname}-${pkgver}.tar.gz")
md5sums=('hash of the source')

build() {
	cd "${pkgname}-${pkgver}"
	./configure --prefix=/usr --mandir=/usr/share/man
	make all
}

package() {
	cd "${pkgname}-${pkgver}"
	make DESTDIR="$pkgdir/" install
}

system admin

https://drewdevault.com/new-server

web design

CSS - center a div (not a joke!)
.xyz {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
}
CSS - order : top,right,bottom,left
div {
    padding: 25px 50px 75px 100px;
    /* top: 25px ; right: 50px; bottom: 75px; left: 100px */
}

MISC

numbers and bases
2^n                   Hex       Unit        Note
-------------------------------------------------------------------------------
2^10                0x400         Ki
-------------------------------------------------------------------------------
2^12               0x1000        4Ki        4k page table
-------------------------------------------------------------------------------
2^20            0x10_0000         Mi
-------------------------------------------------------------------------------
2^30          0x4000_0000         Gi
-------------------------------------------------------------------------------
2^40       0x10_0000_0000         Ti
-------------------------------------------------------------------------------
2^48                    -      256Ti        48 bit virtual address space
-------------------------------------------------------------------------------
2^50                    -         Pi
-------------------------------------------------------------------------------
2^52                    -        4Pi        52 bit physical address space
-------------------------------------------------------------------------------
2^64                    -    16484Pi        64 bit address space
endianess
32bit integer 0x01020304

              1000  1001  1002  1003    <= byte address in RAM
--------------------------------------
Big           0x01  0x02  0x03  0x04     - LSB in higher addr
--------------------------------------
Mixed         0x02  0x01  0x04  0x03     - every two bytes in a LE group
--------------------------------------
Little        0x04  0x03  0x02  0x01     - LSB in lower addr
--------------------------------------

^
|
Endianess

suggestions?

contact me
You can find my contacts on the about page of this website
https://shrik3.com/about/

Critia:
    - prefer one-liners
    - prefer simplicity
    - prefer ascii and textwidth=80
    - those you REALLY keep googling and forgetting
    - not a cliché