if判断文件、目录属性

[-f file]判断是否是普通文件，且存在

[-r file]判断文件是否可读

[-w file]判断文件是否可写

[-x file]判断文件是否可执行

[root@localhost ~]# cd shell/[root@localhost shell]# vi 1.sh添加      1 #!/bin/bash      2 f="/tmp/user"      3 if [ -f $f ]      4 then      5     echo $f exist      6 else      7     touch $f      8 fi[root@localhost shell]# sh -x 1.sh + f=/tmp/user+ '[' -f /tmp/user ']'+ touch /tmp/user[root@localhost shell]# ls /tmp/ks-script-WBlSuE  mysql.sock  pear  php-fcgi.sock  user  yum.log[root@localhost shell]# [root@localhost shell]# [root@localhost shell]# [root@localhost shell]# [root@localhost shell]# sh -x 1.sh + f=/tmp/user+ '[' -f /tmp/user ']'+ echo /tmp/user exist/tmp/user exist[root@localhost shell]# ls /tmp/ks-script-WBlSuE  mysql.sock  pear  php-fcgi.sock  user  yum.log

[root@localhost shell]# vi 1.sh 添加      1 #!/bin/bash      2 f="/tmp/user"      3 if [ -d $f ]      4 then      5     echo $f exist      6 else      7     mkdir $f      8 fi

[root@localhost shell]# vi 1.sh 添加      1 #!/bin/bash      2 f="/tmp/user/"      3 if [ -e $f ]      4 then      5     echo $f exist      6 else      7     mkdir $f      8 fi

if判断的一些特殊用法

if [ -z "$a" ]这个表示当变量a的值为空时会怎么样

if [ -n "$a" ]表示当前变量a的值不为空

if grep -q ‘123’ 1.txt;then表示如果1.txt种含有'123'的行时会怎么样

if [ ! -e file ];then表示文件不存在时会怎么样

if (( $a < 1 ));then...等同于if [ $a -lt 1 ];then ...

[]中不能使用<,>,==,!....等符号

[root@localhost ~]# cd shell/[root@localhost shell]# ls1.sh[root@localhost shell]# if [ -n 1.sh ]; then echo ok; fiok[root@localhost shell]# echo $b[root@localhost shell]# if [ -n "$b" ]; then echo $b; else echo "b is null"; fib is null

[root@localhost shell]# vi 1.sh 添加      1 #!/bin/bash      2 n=`wc -l /tmp/1.txt`      3 if [ -z "$n" ]      4 then      5     echo error      6     exit      7 else      8     if [ $n -gt 100 ]      9     then     10         echo ok     11     fi     12 fi

可以改为

[root@localhost shell]# vi 1.sh 添加      1 #!/bin/bash      2 n=`wc -l /tmp/1.txt`      3 if [ -z "$n" ]      4 then      5     echo error      6     exit      7 elif [ $n -gt 100 ]      8 then      9     echo ok     10 fi[root@localhost shell]# sh -x 1.sh ++ wc -l /tmp/1.txtwc: /tmp/1.txt: No such file or directory+ n=+ '[' -z '' ']'+ echo errorerror+ exit[root@localhost shell]# ls /tmp/ks-script-WBlSuE  mysql.sock  pear  php-fcgi.sock  user  yum.log

1 #!/bin/bash      2 if [ ! -f /tmp/1.txt ]      3 then      4     echo "/tmp/1.txt nnot exist."      5     exit      6 fi      7 n=`wc -l /tmp/1.txt`      8 if [ -z "$n" ]      9 then     10     echo error     11     exit     12 elif [ $n -gt 100 ]     13 then     14     echo ok     15 fi[root@localhost shell]# sh -x 1.sh + '[' '!' -f /tmp/1.txt ']'+ echo '/tmp/1.txt nnot exist.'/tmp/1.txt nnot exist.+ exit

使用变量时建议用双引号标注

[root@localhost shell]# if grep -w 'user1' /etc/passwd; then echo "user1 exist"; fi[root@localhost shell]# if ! grep -w 'user1' /etc/passwd; then echo "user1 exist"; fiuser1 exist

修改于 180207

转载于:https://my.oschina.net/hellopasswd/blog/1619940

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