Shell Step by Step (3)--stdin & IF

4. Input and output

#! /bin/bash# Read users input and then get his nameread"Please input your first name: " firstNameread"Please input your last name: " lastNameecho-e"Your full name is:   $firstName  $lastName"

Read usage:

read[-ers][-a 数组][-d 分隔符][-i 缓冲区文字]      [-n 读取字符数][-N 读取字符数][-p 提示符]      [-t 超时][-u 文件描述符][名称 ...]

5. Conditional discriminant Formula

- eIs there a-nt (newer than) file1 is better than file2 new-ot (older than) file1 than file2 old-neIndicates not equal to-eqEquals, as:if["$a" -eq "$b"]-neNot equal to, as:if["$a" -ne "$b"]-GTGreater than, as:if["$a" -GT "$b"]-ge is greater than or equal to, such as:if["$a"-ge"$b"]-ltLess than, such as:if["$a" -lt "$b"]-le less than equals, such as:if["$a"-le"$b"]< is less than (requires double brackets), such as: (("$a"<"$b") <= is less than or equal (requires double brackets), such as: (("$a"<="$b") > Greater than (requires double brackets), such as: (("$a">"$b") >= is greater than or equal to (requires double brackets), such as: (("$a">="$b")-Z (zero)

[-AFILE] IfFILEThe existence is true. [-BFILE] IfFILEExists and is a block special file is true. [-CFILE] IfFILEexists and is a word special file is true. [-DFILE] IfFILEexists and is a directory is true. [-EFILE] IfFILEThe existence is true. [-FFILE] IfFILEexists and is an ordinary file is true. [-GFILE] IfFILEexists and the Sgid is set to true. [-HFILE] IfFILEIs true if it exists and is a symbolic connection. [-KFILE] IfFILEexists and the sticky bit has been set is true. [-PFILE] IfFILEexists and is a name pipe (f if O) is true. [-RFILE] IfFILEIs true if it exists and is readable. [-SFILE] IfFILEexists and is not of the size0Is true.  [-T FD] true if the file descriptor FD is open and points to a terminal. [-UFILE] IfFILESuid is present and set (SetUser ID) is true. [-WFILE] IfFILEIfFILEIs true if it exists and is writable. [-XFILE] IfFILEIs true if it exists and is executable. [-OFILE] IfFILEexists and is valid user ID is true. [-GFILE] IfFILEexists and is valid user group is true. [-LFILE] IfFILEIs true if it exists and is a symbolic connection. [-NFILE] IfFILEExist andhas beenMoDIf the IED since it is lastReadIs true. [-SFILE] IfFILEexists and is a socket is true.

[File1-nt FILE2] If FILE1 have been changed more recently than FILE2,orIf FILE1 exists andFILE2does  notIs true.  [File1-ot FILE2] If FILE1 is older than FILE2, or FILE2 exists and FILE1 does not exist, it is true.  [File1-ef FILE2] True if FILE1 and FILE2 point to the same device and node number.  [-O Optionname] true if the shell option "Optionname" is turned on.       [-Z STRING]  "STRING" is true if the length is zero. [-N STRING]or[STRING]  The length of "STRING" is not 0 Non-zero is true. [STRING1 = = STRING2] If2The same string. "=" may be usedinstead of"= =" forStrict POSIX compliance is true. [STRING1! = STRING2] True if the strings are not equal. [STRING1 < STRING2] if "STRING1" sortsbefore"STRING2" lexicographicallyinch  theThe current locale is true. [STRING1 > STRING2] If "STRING1" sorts After"STRING2" lexicographicallyinch  theThe current locale is true.    [ARG1 OP ARG2] "OP" isOne of-eq,-ne,-lt,-le,-GTor-ge. These arithmetic binary operatorsreturn true if"ARG1" is                     Equal  to, not Equal  to,Less than, less thanor Equal  to,Greater than,or                     Greater than or Equal  to"ARG2", respectively. "ARG1" and"ARG2" is integers.

e.g:

if"$UID"-ne"$ROOT_UID" ]  then ……

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Shell Step by Step (3)--stdin & if