Shell

变量之间用空格分隔

terminal 怎么知道这些程序的？有一个东西叫做环境变量 (environment variable)，是给一个编程语言的用的变量。是每当 shell 启动时就有的变量，而不是你在 shell 中设的变量 废话

没错，shell 也是一个编程语言，它可以用控制语句，shell scripting。

Basic command

echo $PATH  # print all PATH the shell will look for
which date  # print where the program is
pwd         # print working directory
cd ./Jinix  # change directory to Jinix in current directory
ls /        # list the file in current directory, 0 or more path para
mv 1.c 11.c # move f & d, require two paths; *or can rename*
cp 1.c 11.c # copy only file
cp -r dir1 dir2 # but can provide '-r', for recursion cp to copy a dir
rm 1.c      # remove only file, but similarly:
rm -r dir1
rmdir dir1  # remove dir only if the dir is empty
mkdir My Photos # make two dirs named 'My' & 'Photos' respectively
man rmdir   # show manual of program 'rmdir'

Special word

cd ~/Desktop # tilde for the home directory
cd -         # dash for the previous dir, a handy way to toggle between two dirs
ls --help    # --help will show the usage 

About "Path"

诶哟，原来 . 代表当前目录，.. 代表父目录，不用加 /。因此 cd .. 代表去往 the parent directory of current. 确实，本来目录最后一个都不用加斜杠的

而且目录的话，当前文件夹下的东西是可以不用加 ./ 的。(注意，“目录的话”，也就是得让 shell 知道这是个目录)

easyDecode  # a environment variable? a program? The former
# a program in the relevent directory
Self-madeTools/easyDecode
# echo a "world" word
../../bin/echo world
cd Self-madeTools/

但是也许需要它是目录的时候，给他一个 / 指明会更好？

Permission of files and directory

如果你有一个文件的w，但是没有这个文件所在目录的w，那么你可以 empty it, but cannot delete it

dx determine whether you can cd in the directory，同时需要他的父目录都要x

Stream