shell条件表达式
以下是从man bash出来的文档，并对相关文字进行翻译(持续更新)
- -a file 为真条件：文件存在。
- -b file True if file exists and is a block special file.
- -c file True if file exists and is a character special file.
- -d file 为真条件：文件存在并且文件是个目录(文件夹)。
- -e file 为真条件：文件存在。
- -f file True if file exists and is a regular file.
- -g file True if file exists and is set-group-id.
- -h file True if file exists and is a symbolic link.
- -k file True if file exists and its ``sticky’’ bit is set.
- -p file True if file exists and is a named pipe (FIFO).
- -r file 为真条件：文件存在并且文件可读。
- -s file True if file exists and has a size greater than zero.
- -t fd True if file descriptor fd is open and refers to a terminal.
- -u file True if file exists and its set-user-id bit is set.
- -w file 为真条件：文件存在并且文件可写。
- -x file 为真条件：文件存在并且文件可执行。
- -O file True if file exists and is owned by the effective user id.
- -G file True if file exists and is owned by the effective group id.
- -L file True if file exists and is a symbolic link.
- -S file True if file exists and is a socket.
- -N file True if file exists and has been modified since it was last read.
- file1 -nt file2 为真条件：文件1比文件2新(根据修改日期)，或者文件1存在文件2不存在。
- file1 -ot file2 为真条件：文件1比文件2旧，或者文件1不存在文件2存在。
- file1 -ef file2 为真条件：文件1和2指向相同设备 (device)和索引节点(inode numbers).
- -o optname True if shell option optname is enabled. See the list of options under the description of the -o option to the set builtin below.
- -z string 为真条件：字符串长度为零。
- -n string 为真条件：字符串长度不为零。
- string1 == string2 为真条件：字符串相等。 = may be used in place of == for strict POSIX compliance.
- string1 != string2 为真条件：字符不串相等。
- string1 < string2 True if string1 sorts before string2 lexicographically in the current locale.
-
string1 > string2 True if string1 sorts after string2 lexicographically in the current locale.
- arg1 OP arg2 arg1和arg2为整数，OP包括
- -eq 等于
- -ne 不等于
- -lt 小于
- -le 小于等于
- -gt 大于
- -ge 大于等于
