A variable
[root@T_FOOT-Home2-ZZZ01 ~]# a=hello
[root@T_FOOT-Home2-ZZZ01 ~]# echo $a
hello
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${a}_world
hello_world
In fact, $ a $ {A} and the same function, but in order to prevent splicing string, string variables can not distinguish between the computer and splicing, it is necessary to add {}
Two extraction output of the command
[root@T_FOOT-Home2-ZZZ01 ~]# pwd /root [root@T_FOOT-Home2-ZZZ01 ~]# echo $(pwd) /root
Assignment three conditions ($ {var: - / = / / + string?})
1 $ {var: -string}: means if var is empty, then the output value of the string, if var is not empty, then the output value of var
2 $ {var: = string}: refers to a value if var is empty, then the output string, and the string value assigned to var, var values if not empty, then the output of var
3 $ {var:? String}: means if var is empty, then the error message is output -bash: var: string, if the value of var is not empty, then the output of var
4 $ {var: + string}: and $ {var: -string} Conversely, if var is empty, then print the value of var, var if not empty, then print the value of the string
Four $ ((exp))
[root@T_FOOT-Home2-ZZZ01 ~]# echo $((3+2)) 5
Five pattern matching replacement
$ {Var% pattern}, $ {var %% pattern} from the right match
$ {Var # pattern}, $ {var ## pattern} from left to match
$ {Var% pattern}, $ {var # pattern} represents the shortest, the matching to stop
$ {Var %% pattern}, $ {var ## pattern} represents the longest match
Wildcards
*: Zero or more of any character
?: Zero or one character
[...]: matching brackets to indicate character
[...!]: That does not match the characters inside the brackets
[root@T_FOOT-Home2-ZZZ01 ~]# f=a.tar.gz
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f##*.}
gz
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f#*.}
tar.gz
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f%%.*}
a
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f%.*}
a.tar
Six to extract the bytes
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f:0:2}
a.
Get the subscript f is from 0 byte two bytes subsequent
[root@T_FOOT-Home2-ZZZ01 ~]# echo ${f:1}
.tar.gz
After extracting the subscript f is from 1 byte to all bytes
Seven string replacement
${file/dir/path}: Replace the first dir path
${file//dir/path}: Replace all dir path
${#var}：Calculate the value of the variable ${var}length
Eight output redirection
echo "hello world" >> tempfile hello world to copy tempfile to a file, then print it out
Nine input redirection
wc << flag
Its essence is input as a command to output the content cached
Ten Process Control
if-then statement
if xx1 then
xx1s
elif xx2 then
xx2s
else
xx3s
be
Eleven case
case ... esac
Twelve for
Thirteen while
Fourteen until
Fifteen break and continue
Sixteen test command
Referring connected https://blog.csdn.net/aimarrow/article/details/80870180