Chapter Three the wildcards expressions of Linux special character expressions

first, the contents of this chapter

1, special characters

2, the filename wildcard character

3, logical operators and parentheses in multiple commands

4, the command is an expression

Note: This Linux system is RHEL5.3

two, Linux system special characters

1, double quotes

1],$ name= "Mary"

2],echo "Now time: ' Date '" # using inverted quotes to refer to the command output

3],# echo $NAME | grep jhon Alix Error Error

# echo $NAME | grep "Jhon Alix"

2, single quotes

1],$ name= "Mary"

2],echo "Now time: ' Date '" # using inverted quotes to refer to the command output

3],# echo $NAME | grep jhon Alix Error Error

# echo $NAME | grep ' Jhon Alix '

3, the command-quote counter quote

# ls-l ' Cat/etc/shells '

4, variable reference and command converter dollar sign

$ refers to a variable, just precede the variable name with "$"

# Ls-l $ (cat/etc/shells) # referencing command output using a command converter

5, anti-slash screen character

\ Mask The meaning of the special character itself.

# echo "Please pay \$15.50." #使用反斜线屏蔽输出字符串中的 $

three, the filename wildcard character

1,? represents any one character in the matching file name

# Ls-l A?

# Ls-l a??

2,* represents any string in the matching filename, which can be 0 to one character, or a string of long characters.

# ls-l *c

# ls-l Ee*c

# ls-l *c?

3,[] Character range matching, used to match a range of characters, which can be expressed as "-" the range of letters and numbers, or a combination of several characters

# ls-l [klsyz]* #以klsyz中任意字母开头的所有文件

# ls-l A*[CDE]?

4,[!] Exclude range matching, character combinations or alphanumeric ranges that appear in mismatched symbols

# ls-l [0-9][!0-9] #有两个字符, the first is a number, and the second is not a digital

four, logical operators and parentheses in multiple commands

1, logic or "| |"

Command1 | | Command2

Execute Command 1 First, if successful, skip command 2, if failed, execute command 2

# Mail-f/root/mbox | | echo "Permission Denied"

2, logic and "&&"

Command1 && Command2

Execute Command 1 First, if successful, execute command 2, and if it fails, skip command 2

# MV ~/rm.txt/&& echo "successfully moving Files"

3, brackets () and {}

(Command1; command2; Command3 ...)

{command1; command2; Command3 ...}

Execute the commands in parentheses sequentially until all the commands inside the brackets finish, and then return to execute the other commands.

Five, the command is an expression

1, "." A single character match, placed in the "//"

"/.i....../"

"/27210103../"

2, "*" single character or string repetition match, used to match one or more occurrences of individual characters or sequences of characters.

"/bo * *" can be matched, Bo, Boo, booooo ...

3, "^" line start match, used to indicate the line header position string or pattern in the match

"/^l/"

"/^2721010325/"

Regular expressions do not have a matching filename feature. Therefore, you cannot use the above mode directly on the Ls-l command, and you can leave the above mode to some filtering commands, such as the grep command: ls-l | Gerp/^l/

4, "$" line-end match, used to match string patterns at the end of each line of text, followed by matching strings

"/^ ... $l/" Match all lines with only 5 characters

"/love$/" matches the line at the end of love.

5, "\" backslash shield, such as shielding #,;, ', ',:, *, ^, $,?, [], etc

# expr 256 \* 256

"/\^\^\.txt/" Matching ^^.txt

6, "[]" matching character

"/[ll]ove/" matches love, Love

"/[^a-z]/" indicates that all letters are not matched

7, "\<", "\> Word first match, final match character

"/\<love/" matches all text with love as its first word

"/love\>/" matches all text ending with love

8, "x\{\}" repeat times match

"/M\{5\}/" matches text with 5 occurrences of M

Text with a "/M\{5,\}/" Match m occurrence of at least 5 times

"/M\{5,10\}/" matches text with 5 to 10 occurrences of M

9, using regular expressions in combination

"/^$/" matches a blank line

"/^.*$/" is used to match an entire line: fills the entire row with one character.

"/^[tt]he/" matches all rows beginning with the "or"

"/^[^tt]he/" excludes all rows with the beginning of the "or"

"/[0-9]\{1,3}\. [0-9]\{1,3}\. [0-9]\{1,3}\. [0-9]\{1,3}\/] matches an IP address

"/\<love\>/" Exact match love