Shell and regular expressions

Shell expression

Whether the-D file exists and is a directory

The-f file is present and is a normal file

Whether the-W file file exists and is writable

-s file exists and is not empty

-N string string length not 0

String1=string2 string Equality

-eq equals

-GT Greater than

-lt less than

Whether the-e file exists

-R file exists and is readable

The-x file file exists and is executable

Whether the-h file is a linked file

-Z String string length is 0

String1!=string2 String Range

-ge greater than or equal to

-le less than or equal to

-ne Not equal to

Single quotation marks

Echo ' $HOME '

$HOME

echo "$HOME"

/root

echo "\ $HOME"

Escape

echo "ABC ' Date +%d '"

ABC 12/07/16

echo "ABC $ (date +%d)"

ABC 12/07/16

Regular expressions

. Match any single character

* Match previous character appears 0 or more times

. * Match any number of arbitrary strings

[] matches any single character in the collection

[x-y] matches a contiguous range of strings

^ Match string start

$ Match String End

[^] Match negation, reverse the set in parentheses

\ matches the escaped string

\{n,m\} matches the previous character repeats N to M times

\{n,\} matches the previous character at least n times

\{n\} matches the previous string repeated n times

\ (\) stores the contents between \ (and \) in "Reserved Space" with a maximum of 9 storage

\ NAND \1 to \9 to call the contents of the reserved space

{n,m} is equivalent to \{n,m\}

+ matches one or more occurrences of the previous character

? Matches the previous character one or 0 times

| Logical OR, match before or after string

() match a regular set

eg
Grep:.. 0:passwd

grep 00* passwd

grep o[oa]t passwd

grep [0-9] passwd

grep ^root passwd

grep bash$ passwd

grep Sbin/[^t] passwd

grep ' 0\{1,2\} ' passwd

grep "\ (root\) \ (: \). *\2\1" passwd

grep ^$ passwd

Grep-v ^$ passwd

This article is from the Linux Learning Notes blog, so be sure to keep this source http://rockycai.blog.51cto.com/8871643/1881674

Shell and regular expressions