My Way on Linux-[Shell Basics]-a common method of judging whether a file, directory exists, or whether it has a certain class of attributes (permissions) in the Bash shell

Conditional Logic on Files # Determine if the file exists and the file type

-Afileexists. #文件存在-BfileExists and is a block specialfile. #文件存在, and it's a block device.-Cfileexists and is a character specialfile. # #文件存在, and is a character device-Dfileexists and is a directory. #文件存在, and is the directory-EfileExists (just the same as-a). #文件存在-Ffileexists and is a regularfile. #文件存在, and is an ordinary file-Lfileexists and is a symbolic link. #文件存在, and Symbolic links-Pfileexists and is a firstinch, first Out (FIFO) Specialfileor named pipe. #文件存在, and is a piping or FIFO device-Sfileexists and is a socket. #文件存在, and is a socket (socket) file-Sfileexists and has a size greater than zero. #文件存在, and file non-0 (greater than 0)

# Determine if the file exists and has the properties of the relevant permission

# General Properties-Rfileexists and is readable by the current process. #文件存在, and this process is readable-W    fileexists and is writable by the current process. #文件存在, and this process can be written-Xfileexists and is executable by the current process. #文件存在, and this process can execute # Extended Properties-Ufileexists and have its setuid (2) bit set. #文件存在, and has the Setuid property-Gfileexists and have its setgid (2) bit set. #文件存在, and has the Setgid property-Kfileexists and have its sticky bit set. #文件存在, and has sticky bits-Gfileexists and have the same group ID as this process. #文件存在, and has the same GID as this process-Ofileexists and is owned by the user ID of this process. #文件存在, and has the same UID as this process

# character length judgment

-Z    string  length is zero.    #字符串长度为零返回true-N    string length is not zero.    #字符串长度非零返回true

# Other options ( this place is not very understanding, please enlighten me )

-T    file Descriptor number Fildes is open and associated with a terminal device.    # file descriptor?? is open and is related to the terminal device- o    Named option is set on.    # turn on the naming option??

# Two comparisons between files

-NT    #newer than, to determine whether file1 is newer than file2, by comparing the time stamp of the file to achieve -ot    #older than, to determine whether File1 is older than file2, by comparing the timestamp implementation of the file /c2>-ef    file, to determine whether File2 and File2 is the same file, by judging the two files pointing to the inode is the same to achieve, can be used in hard link decision

# Two integers in a comparison

-eq    #equal  equals -ne    #not equal  not equal -GT    #greater than  greater than - Lt    #  less than  smaller than -ge    #greater than or equal  greater than or equal to-le    #  less than or equal  smaller than or equal to

# Multiple conditional judgments

-a    #and logic and, when both conditions are true--o    #or logic or, if any of the two conditions istrue!     #not logical non, reverse state returns True

Shell Examples of common judgments

#!/bin/Bashmypath="/var/log/nginx/"myfile="/var/log/nginx/access.log"# -The x parameter determines whether the $mypath exists and has executable permissionsif [!-X"$myPath"];ThenMkdir"$myPath"Fi# -The D parameter determines whether the $mypath exists, and the attribute is a directoryif [!-D"$myPath"];ThenMkdir"$myPath"Fi# -The f parameter determines whether the $myfile exists, and the attribute is a normal fileif [!-F"$myFile" ];ThenTouch"$myFile"Fi# -The n parameter determines whether a variable has a valueif [!-N"$myVar" ];ThenEcho"$myVar is empty"exit 0fi# Two variables determine if equal if [ "$var 1"= "$var 2"]; thenecho '$var 1 eq $var 2'elseecho '$var 1 not EQ $var 2'fi  

My Way on Linux-[Shell Basics]-a common method of judging whether a file, directory exists, or whether it has a certain class of attributes (permissions) in the Bash shell