Detailed explanation of command-test
The test command is a practical tool for testing conditional expressions in the shell environment.
test(选项)
-b:如果文件为一个块特殊文件,则为真; -c:如果文件为一个字符特殊文件,则为真; -d:如果文件为一个目录,则为真; -e:如果文件存在,则为真; -f:如果文件为一个普通文件,则为真; -g:如果设置了文件的SGID位,则为真; -G:如果文件存在且归该组所有,则为真; -k:如果设置了文件的粘着位,则为真; -O:如果文件存在并且归该用户所有,则为真; -p:如果文件为一个命名管道,则为真; -r:如果文件可读,则为真; -s:如果文件的长度不为零,则为真; -S:如果文件为一个套接字特殊文件,则为真; -u:如果设置了文件的SUID位,则为真; -w:如果文件可写,则为真; -x:如果文件可执行,则为真。
Common usage of test in shell programming in Linux:
Judgement expression
if test #表达式为真 if test ! #表达式为假 test 表达式1 –a 表达式2 #两个表达式都为真 test 表达式1 –o 表达式2 #两个表达式有一个为真 test 表达式1 ! 表达式2 #条件求反
Judge string
test –n 字符串 #字符串的长度非零 test –z 字符串 #字符串的长度是否为零 test 字符串1=字符串2 #字符串是否相等,若相等返回true test 字符串1!=字符串2 #字符串是否不等,若不等反悔false
Judge integers
test 整数1 -eq 整数2 #整数相等 test 整数1 -ge 整数2 #整数1大于等于整数2 test 整数1 -gt 整数2 #整数1大于整数2 test 整数1 -le 整数2 #整数1小于等于整数2 test 整数1 -lt 整数2 #整数1小于整数2 test 整数1 -ne 整数2 #整数1不等于整数2
Judgement file
test File1 –ef File2 两个文件是否为同一个文件,可用于硬连接。主要判断两个文件是否指向同一个inode。 test File1 –nt File2 判断文件1是否比文件2新 test File1 –ot File2 判断文件1比是否文件2旧 test –b file #文件是否块设备文件 test –c File #文件并且是字符设备文件 test –d File #文件并且是目录 test –e File #文件是否存在 (常用) test –f File #文件是否为正规文件 (常用) test –g File #文件是否是设置了组id test –G File #文件属于的有效组ID test –h File #文件是否是一个符号链接(同-L) test –k File #文件是否设置了Sticky bit位 test –b File #文件存在并且是块设备文件 test –L File #文件是否是一个符号链接(同-h) test –o File #文件的属于有效用户ID test –p File #文件是一个命名管道 test –r File #文件是否可读 test –s File #文件是否是非空白文件 test –t FD #文件描述符是在一个终端打开的 test –u File #文件存在并且设置了它的set-user-id位 test –w File #文件是否存在并可写 test –x File #文件属否存在并可执行
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