CentOS 7 Shell腳本編程第九講 條件測試和判斷

經常使用條件測試有 test 命令，[] [[]]等。

##-f 檢查是否爲文件
[root@promote ~]# ls
anaconda-ks.cfg test.txt 
[root@promote ~]# test -f test.txt && (echo 0 || echo 1)
0
[root@promote ~]# test -f test1.txt && (echo 0 || echo 1)
[root@promote ~]# test -f test.txt && echo 0 || echo 1
0
[root@promote ~]# test -f test.txt1 && echo 0 || echo 1
1
[root@promote ~]#

詳細信息請看。

文件表達式
-e:文件存在
-f:表示這個文件是個通常文件(regular file)(不是目錄或者設備文件) 
文件表達式
-e filename 若是 filename文件存在，則爲真
-d filename 若是 filename爲目錄，則爲真 
-f filename 若是 filename爲是般文件(regular file)(不是目錄或者設備文件)，則爲真
-L filename 若是 filename爲符號連接，則爲真
-r filename 若是 filename可讀，則爲真 
-w filename 若是 filename可寫，則爲真 
-x filename 若是 filename可執行，則爲真
-s filename 若是文件長度不爲0，則爲真
-h filename 若是文件是軟連接，則爲真
filename1 -nt filename2 若是 filename1比 filename2新，則爲真。
filename1 -ot filename2 若是 filename1比 filename2舊，則爲真。

整數變量表達式
比較符號          (( ))中[[ ]]使用符號    說明
-eq 等於              ==或=               equal
-ne 不等於             !=                  not equal
-gt 大於               >                   greater than
-ge 大於等於           >=                  greater equal
-lt 小於               <                   less than
-le 小於等於           <=                  less equal

條件判斷中test 和 [ ]等價。(( ))支持簡單運算，[ ] 與[[]]不支持，[[ ]]支持&&和||。比較運算符先後推薦添加空格。

詳細用法能夠查看幫助。

#沒有全面列舉
[root@promote ~]# man test
[root@promote ~]# man bash
[root@promote ~]# info bash
[root@promote ~]# man bash

#部分幫助文件以下
      -a FILE        True if file exists.
      -b FILE        True if file is block special.
      -c FILE        True if file is character special.
      -d FILE        True if file is a directory.
      -e FILE        True if file exists.
      -f FILE        True if file exists and is a regular file.
      -g FILE        True if file is set-group-id.
      -h FILE        True if file is a symbolic link.
      -L FILE        True if file is a symbolic link.
      -k FILE        True if file has its `sticky' bit set.
      -p FILE        True if file is a named pipe.
      -r FILE        True if file is readable by you.
      -s FILE        True if file exists and is not empty.
      -S FILE        True if file is a socket.
      -t FD          True if FD is opened on a terminal.
      -u FILE        True if the file is set-user-id.
      -w FILE        True if the file is writable by you.
      -x FILE        True if the file is executable by you.
      -O FILE        True if the file is effectively owned by you.
      -G FILE        True if the file is effectively owned by your group.
      -N FILE        True if the file has been modified since it was last read.

注意對比如下代碼輸出結果。

[root@promote ~]# [ -f /etc/passwd -a /etc/services ] && echo 0 || echo 1
0
[root@promote ~]# [[ -f /etc/passwd -a /etc/services ]] && echo 0 || echo 1 #錯誤使用-a
[root@promote ~]# [[ -f /etc/passwd && /etc/services ]] && echo 0 || echo 1
0
[root@promote ~]# [ -f /etc/passwd && /etc/services ] && echo 0 || echo 1 #錯誤使用&&

本節內容經過一段簡單代碼結束。

#只能輸入數字一、二、3
#save a .sh file
#!/bin/bash
testdir=/root/testdir
[! -d testdir ] && mkdir -p /root/testdir
cat << END
	1.[install lamp]
	2.[install lnmp]
	3.[exit]
	please input 1 or 2 or 3 :
END
read input
expr $input + 0 &>/dev/null #Not necessarily 0, /dev//null means not output to standard output interface
[ $? -ne 0 ] && {
	echo "please input {1|2|3}"
	exit 1
}
[ $? -ne 1 ] && {
	echo "Start install lamp ..."
	exit 1
}
[ $? -ne 2 ] && {
	echo "Start install lnmp ..."
	exit 1
}

[root@promote ~]# ls
anaconda-ks.cfg  get-docker.sh  install_mongodb.sh  test  testdir.sh  test.txt  users
[root@promote ~]# 

#簡單目錄是否存在判斷
#查看文件內容
[root@promote ~]# cat testmkdir.sh 
#!/bin/bash
if [ ! -d /root/var/testdir ] ;then
mkdir -p /root/var/testdir
fi 
#執行腳本
[root@promote ~]# bash testmkdir.sh 
[root@promote ~]# ls /root/var/testdir | grep t
testdir
[root@promote ~]#