shell 学习笔记

#!/bin/bash

# shell 学习笔记

#Create a temporary file or directory, safely, and print its name.
# -d, --directory     create a directory, not a file
export TMP_DIR='mktemp -d'

# $? is used for checking return result

readlink :

readlink - print value of a symbolic link or canonical file name

       -f, --canonicalize
              canonicalize  by  following every symlink in every component of the given name recursively; all but the
              last component must exist

一般使用 readlink -f .

-f 使用和不使用的区别是 -f 会 递归找最终的链接，不加 -f 就直接一级。

$ mkdir -p ~/wrwork/bash

$ cd ~/wrwork/bash

$ ln -s ~/Downloads test

$ ln -s test test1

$ readlink -f test1

/home/chenqiang/Downloads

$ readlink test1

test

       which - locate a command

SYNOPSIS
       which [-a] filename ...

DESCRIPTION
       which  returns  the  pathnames of the files (or links) which would be executed in the current environment, had
       its arguments been given as commands in a strictly POSIX-conformant shell.  It does this by searching the PATH
       for executable files matching the names of the arguments. It does not follow symbolic links.

chenqiang@qiang:~/wrwork/bash$ which git >/dev/null
chenqiang@qiang:~/wrwork/bash$ echo $?