A small gift for beginners of bash-Linux general technology-Linux programming and kernel information. The following is a detailed description. Some common mistakes in bash programming come from abs-guide
Note !!!! All the examples here are incorrect !!!
===== Variable usage ====
1. Define the bash reserved string as a variable name/variable name containing reserved characters
Case = 123 # case is a reserved string
Ca (= 123 # (Reserved characters)
Var-1 = 123 #-is reserved characters, var_1 is good
2. The variable starts with a number.
12var = 123.
3. Duplicate variables and function definitions
Do_something ()
{
Echo "This function does something with \" $1 \"."
}
Do_something = do_something
Do_something
4. Variable assignment = space on both sides
Var1 = 123 # var1 = 123
===== Compare [] ====
5. Space is missing in []
[$ Var-eq 5]
[$ Var = AB]
6. <> do not add \
[$ Var <AB] # in this case, <> is interpreted as output redirection, and [$ var \ <AB] is
7. =\> \ <与 -eq -gt -lt不分
[$ Var-eq 45.6] #=\> \ <用来比较字串，而eq gt lt只能用来比较整数，注意是整数，不是数值
8. The sha-bang script cannot contain invalid characters. The content written in dos/win is wrapped in \ r \ n. The actual number of lines in the script is #! /Bin/bash \ r \ n, but only #! /Bin/bash \ n is valid
9. the operation on the variable in the sub-shell cannot be passed to its parent shell.
Var = 123.
($ Var = 456)
Echo $ var # The result is 123 instead of 456.
Echo 456 | read var
Echo $ var # The result is still 123. The pipeline will issue a sub-shell.
