Linux shell if conditional expression summary __linux

Overview: In Linux shell programming, there are many conditional expressions for comparison/judgment, and this article makes a brief summary of them. 1. String comparison! Take the anti-n str string STR is NOT NULL
-Z str string str is NULL
STR1 = str2 str1 is the same as str2
STR1!= str2 str1 is different from str2 2. Numerical size comparisonInt1-eq Int2 equals
Int1-le Int2 less than or equal
Int1-ge Int2 is greater than or equal to
Int1-lt Int2 less than
INT1-GT Int2 is greater than
Int1-ne Int2 is not equal to
3. File attribute judgment-B Whether block file-C is a character file-D whether a directory-e file exists-F whether normal file-G sets the file's SGID bit-G file to the group all-H whether symbolic connection and- L the same-K file whether the paste bit is set-O is the user all-P file is a named pipe
-R file is readable
-S file is not a zero length
-S is the socket file-T FD fd whether the SUID bit of the file is set on a terminal
is the-W file writable
-X file is executable 4. Comparison of file relationshipsExpr1-a expr2 True if Expr1 and Expr2 are true
Expr1-o expr2 True if Expr1 or EXPR2 is true

File1-ef file2 file1 and file2 have the same inode number file1-nt file2 file1 than file2 new File1-ot file2 older than file1
Important: The expression Non-zero in C language is true, and the IF expression 0 in the shell is true. Normally, if we want to determine whether a script is to be executed from scratch to the tail or midway through a command such as exit 1, we usually add a sentence at the end of the script. /bin/true ", after adding this sentence, the script return value will become 0.