Linux man test

Linux man test         先來看看Linux下對test的解釋（使用man test或者info test） [plain] TEST(1)                               FSF                              TEST(1)    NAME         test - check file types and compare values    SYNOPSIS         test EXPRESSION         [ EXPRESSION ]         test 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           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 evaluates to  the  length         of STRING.    AUTHOR         Written by FIXME: ksb and mjb.    REPORTING BUGS         Report bugs to <bug-coreutils@gnu.org>.    COPYRIGHT         Copyright (C) 2002 Free Software Foundation, Inc.         This is free software; see the source for copying conditions.  There is         NO warranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR         PURPOSE.    SEE ALSO         The  full documentation for test is maintained as a Texinfo manual.  If         the info and test programs are properly installed  at  your  site,  the         command                  info test           should give you access to the complete manual.    GNU coreutils 4.5.3              February 2003                         TEST(1)            再看兩個簡單的例子： [plain] #樣本一  #!/bin/bash    #iftest2    echo -n "Enter your name:"    read NAME    #did the user just hit return    if [ "$NAME" == "" ];    then            echo "You did not enter any infomation"    else            echo "Your name is ${NAME}"      #樣本二  #!/bin/bash    #ifelif    echo -n "Enter your name:"    read NAME    if [ -z $NAME ] || [ "$NAME" = "" ];    then            echo "You did not enter a name."    elif [ "$NAME" = "root" ];    then            echo "Hello root"    elif [ "$NAME" = "chinaitlab" ];    then            echo "Hello chinaitlab"    else            echo "You are not root or wgb,but hi,$NAME"    fi             小技巧：        1.Linux對Shell的要求很嚴格，不要把代碼潔癖（比如定義變數的空格、if、while等等中為了美觀留下的空格）帶到Linux Shell編程中，稍不注意就會報錯；         2.多用man或者info，會收到意想不到的收穫。