Shell comparison and judgment

Comparison and judgment are the elements of program flow control. This article summarizes shell comparison and judgment statements for ease of searching and using.

1. Important comparison Operators

Greater than:-GT

Less than:-lt

Greater than or equal to:-Ge

Less than or equal to:-le

Equal to:-EQ

Not equal to:-ne

Example:

If [$ var-EQ 0] # If $ VaR is equal to 0

If [$ var-Ne 0-A $ var-GT 2] # logic and-

If [$ var-Ne 0-o $ var-GT 2] # logic or-o

2. File-related judgment test

[-F $ file_var]: returns true if $ file_var is an existing file path or file name;

[-X $ var]: returns true if $ VaR has the file executable permission;

[-D $ var]: returns true if $ VaR is a directory;

[-E $ var]: returns true if $ VaR is an existing file;

[-C $ var]: returns true if $ VaR is an existing character device file;

Attached English:

-A file exists. 
-B file exists and is a block special file. 
-C file exists and is a character special file. 
-D file exists and is a directory. 
-E file exists (just the same as-). 
-F file exists and is a regular file. 
-G file exists and has its setgid (2) bit set. 
-G file exists and has the same group ID as this process. 
-K file exists and has its sticky bit set. 
-L file exists and is a symbolic link. 
-N string length is not zero. 
-O named option is set on. 
-O file exists and is owned by the user ID of this process. 
-P file exists and is a first in, first out (FIFO) special file or  Named Pipe. 
-R file exists and is readable by the current process. 
-S file exists and has a size greater than zero. 
-S file exists and is a socket. 
-T file descriptor number Fildes is open and associated with  Terminal device. 
-U file exists and has its setuid (2) bit set. 
-W file exists and is writable by the current process. 
-X file exists and is executable by the current process. 
-Z string length is zero. 

Example:

Fpath = "etc/passwd"

If [-e $ fpath]; then

Echo "file exists ";

Else

Echo "not exist ";

Fi

3. String comparison

[[$ Str1 = $ str2]: returns true if str1 is equal to str2;

[[$ Str1 = $ str2]: This is another way to judge whether a string is equal;

[[$ Str1! = $ Str2]: returns true if str1 is not equal to str2;

[[$ Str1> $ str2]: returns true if str1 is greater than str2;

[[$ Str1 <$ str2]: returns true if str1 is smaller than str2;

[[-Z $ str1]: returns true if str1 contains a null string;

[[-N $ str1]: returns true if str1 contains a non-null string;

Shell comparison and judgment