linux的条件判断

想知道怎么判断一个文件是否存在？是否可执行？是否只读？字符串是否匹配？不记得语法了？
其实只要man test就行啦。很容易明白。

$ man test
[(1)                                                      User Commands                                                      [(1)

NAME
       test - check file types and compare values

SYNOPSIS
       test EXPRESSION
       [ EXPRESSION ]
       [ OPTION

DESCRIPTION
       Exit with the status determined by EXPRESSION.

       --help display this help and exit

       --version
              output version information and exit

       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

       -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

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

       -G FILE
              FILE exists and is owned by the effective group ID

       -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 is readable

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t [FD]
              file descriptor FD (stdout by default) is opened on a terminal

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

       -w FILE
              FILE exists and is writable

       -x FILE
              FILE exists and is executable

       Beware that parentheses need to be escaped (e.g., by backslashes) for shells.  INTEGER may also be -l STRING, which evalu-
       ates to the length of STRING.

AUTHOR
       Written by Kevin Braunsdorf and Matthew Bradburn.

REPORTING BUGS
       Report bugs to <[e-mail]>.

COPYRIGHT
       Copyright <81>0<84>8 2004 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or  FIT-
       NESS FOR A PARTICULAR PURPOSE.

SEE ALSO
       The full documentation for [ is maintained as a Texinfo manual.  If the info and [ programs are properly installed at your
       site, the command

              info coreutils test

       should give you access to the complete manual.

[ 5.2.1                                                    October 2004                                                      [(1)