shell脚本if语句的多种条件参数-白红宇

shell脚本if语句的多种条件参数

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发布时间：2019-06-21

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if语句有多种写法

[root sh]# [ -f file ] && echo "yes" || echo "no"

yes

修改如下：

if [ -f file ]

then

echo "yes"

else

echo "no"

简写：

[ -f file ] && echo "yes"

表示if条件成立时返回yes

[ -f file ] || echo "no"

表示if条件不成立时，返回no

可以用if判断如下条件：

实际上if的条件就是test命令的参数

[omcr@lnltedmr3 ~]$ man test

TEST(1) User Commands TEST(1)

NAME

test - check file types and compare values

SYNOPSIS

test EXPRESSION

test

[ EXPRESSION ]

[ ]

[ OPTION

DESCRIPTION

Exit with the status determined by EXPRESSION.

--help display this help and exit

--version

output version information and exit

An omitted EXPRESSION defaults to false. Otherwise, EXPRESSION is true or false and sets exit status. It is one of:

( EXPRESSION )

EXPRESSION is true

! EXPRESSION

EXPRESSION is false

EXPRESSION1 -a EXPRESSION2

both EXPRESSION1 and EXPRESSION2 are true

EXPRESSION1 -o EXPRESSION2

either EXPRESSION1 or EXPRESSION2 is true

-n STRING

the length of STRING is nonzero

STRING equivalent to -n STRING

-z STRING

the length of STRING is zero

STRING1 = STRING2

the strings are equal

STRING1 != STRING2

the strings are not equal

INTEGER1 -eq INTEGER2

INTEGER1 is equal to INTEGER2

INTEGER1 -ge INTEGER2

INTEGER1 is greater than or equal to INTEGER2

INTEGER1 -gt INTEGER2

INTEGER1 is greater than INTEGER2

INTEGER1 -le INTEGER2

INTEGER1 is less than or equal to INTEGER2

INTEGER1 -lt INTEGER2

INTEGER1 is less than INTEGER2

INTEGER1 -ne INTEGER2

INTEGER1 is not equal to INTEGER2

FILE1 -ef FILE2

FILE1 and FILE2 have the same device and inode numbers

FILE1 -nt FILE2

FILE1 is newer (modification date) than FILE2

FILE1 -ot FILE2

FILE1 is older than FILE2

-b FILE

FILE exists and is block special

-c FILE

FILE exists and is character special

-d FILE

FILE exists and is a directory

-e FILE

FILE exists

-f FILE

FILE exists and is a regular file

-g FILE

FILE exists and is set-group-ID

-G FILE

FILE exists and is owned by the effective group ID

-h FILE

FILE exists and is a symbolic link (same as -L)

-k FILE

FILE exists and has its sticky bit set

-L FILE

FILE exists and is a symbolic link (same as -h)

-O FILE

FILE exists and is owned by the effective user ID

-p FILE

FILE exists and is a named pipe

-r FILE

FILE exists and read permission is granted

-s FILE

FILE exists and has a size greater than zero

-S FILE

FILE exists and is a socket

-t FD file descriptor FD is opened on a terminal

-u FILE

FILE exists and its set-user-ID bit is set

-w FILE

FILE exists and write permission is granted

-x FILE

FILE exists and execute (or search) permission is granted

Except for -h and -L, all FILE-related tests dereference symbolic links. Beware that parentheses need to be escaped

(e.g., by backslashes) for shells. INTEGER may also be -l STRING, which evaluates to the length of STRING.

NOTE: [ honors the --help and --version options, but test does not. test treats each of those as it treats any other

nonempty STRING.

NOTE: your shell may have its own version of test and/or [, which usually supersedes the version described here. Please

refer to your shell's documentation for details about the options it supports.

GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report test translation bugs to <http://translation‐

project.org/team/>

AUTHOR

Written by Kevin Braunsdorf and Matthew Bradburn.

<http://gnu.org/licenses/gpl.html>.

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.