15.1 \u6761\u4ef6\u5224\u65ad\uff1a<\/p>\n\n\n\n
\u5982\u679c\u7528\u6237\u4e0d\u5b58\u5728<\/p>\n\n\n\n
\u6dfb\u52a0\u7528\u6237\uff0c\u7ed9\u5bc6\u7801\u5e76\u663e\u793a\u6dfb\u52a0\u6210\u529f\uff1b<\/p>\n\n\n\n
\u5426\u5219<\/p>\n\n\n\n
\u663e\u793a\u5982\u679c\u5df2\u7ecf\u6ca1\u5728\uff0c\u6ca1\u6709\u6dfb\u52a0\uff1b<\/p>\n\n\n\n
\u6761\u4ef6\u5224\u65ad\uff0c\u63a7\u5236\u7ed3\u6784\uff1a<\/p>\n\n\n\n
1\u3001\u5355\u5206\u652fif\u8bed\u53e5<\/p>\n\n\n\n
if \u5224\u65ad\u6761\u4ef6; then<\/p>\n\n\n\n
statement1<\/p>\n\n\n\n
statement2<\/p>\n\n\n\n
…<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
\u53cc\u5206\u652f\u7684if\u8bed\u53e5\uff1a<\/p>\n\n\n\n
if \u5224\u65ad\u6761\u4ef6; then<\/p>\n\n\n\n
statement1<\/p>\n\n\n\n
statement2<\/p>\n\n\n\n
…<\/p>\n\n\n\n
else<\/p>\n\n\n\n
statement3<\/p>\n\n\n\n
statement4<\/p>\n\n\n\n
…<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
2\u3001\u591a\u5206\u652f\u7684if\u8bed\u53e5\uff1a<\/p>\n\n\n\n
if \u5224\u65ad\u6761\u4ef61; then<\/p>\n\n\n\n
statement1<\/p>\n\n\n\n
…<\/p>\n\n\n\n
elif \u5224\u65ad\u6761\u4ef62; then<\/p>\n\n\n\n
statement2<\/p>\n\n\n\n
…<\/p>\n\n\n\n
elif \u5224\u65ad\u6761\u4ef63; then<\/p>\n\n\n\n
statement3<\/p>\n\n\n\n
…<\/p>\n\n\n\n
else<\/p>\n\n\n\n
statement4<\/p>\n\n\n\n
…<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
15.2 bash\u4e2d\u5982\u4f55\u5b9e\u73b0\u6761\u4ef6\u5224\u65ad\uff1f<\/p>\n\n\n\n
1\u3001\u5b9e\u73b0\u65b9\u6cd5\uff1a<\/p>\n\n\n\n
1\u3001\u67e5\u770b\u72b6\u6001\u8fd4\u56de\u503c<\/p>\n\n\n\n
2\u3001\u6761\u4ef6\u6d4b\u8bd5\u7c7b\u578b\uff1a<\/p>\n\n\n\n
1\u3001\u6574\u6570\u6d4b\u8bd5\uff1a\u5224\u65ad\u6574\u6570\u662f\u5426\u6b63\u786e<\/p>\n\n\n\n
2\u3001\u5b57\u7b26\u6d4b\u8bd5<\/p>\n\n\n\n
3\u3001\u6587\u4ef6\u6d4b\u8bd5<\/p>\n\n\n\n
3\u3001\u6761\u4ef6\u6d4b\u8bd5\u7684\u8868\u8fbe\u5f0f\uff1a<\/p>\n\n\n\n
1\u3001[ expression ]<\/p>\n\n\n\n
2\u3001[[ expression ]]<\/p>\n\n\n\n
3\u3001test expression<\/p>\n\n\n\n
4\u3001\u6574\u6570\u6bd4\u8f83:<\/p>\n\n\n\n
-eq: \u6d4b\u8bd5\u4e24\u4e2a\u6574\u6570\u662f\u5426\u76f8\u7b49\uff1b\u6bd4\u5982 $A -eq $B<\/p>\n\n\n\n
-ne: \u6d4b\u8bd5\u4e24\u4e2a\u6574\u6570\u662f\u5426\u4e0d\u7b49\uff1b\u4e0d\u7b49\uff0c\u4e3a\u771f\uff1b\u76f8\u7b49\uff0c\u4e3a\u5047\uff1b<\/p>\n\n\n\n
-gt: \u6d4b\u8bd5\u4e00\u4e2a\u6570\u662f\u5426\u5927\u4e8e\u53e6\u4e00\u4e2a\u6570\uff1b\u5927\u4e8e\uff0c\u4e3a\u771f\uff1b\u5426\u5219\uff0c\u4e3a\u5047\uff1b<\/p>\n\n\n\n
-lt: \u6d4b\u8bd5\u4e00\u4e2a\u6570\u662f\u5426\u5c0f\u4e8e\u53e6\u4e00\u4e2a\u6570\uff1b\u5c0f\u4e8e\uff0c\u4e3a\u771f\uff1b\u5426\u5219\uff0c\u4e3a\u5047\uff1b<\/p>\n\n\n\n
-ge: \u5927\u4e8e\u6216\u7b49\u4e8e<\/p>\n\n\n\n
-le\uff1a\u5c0f\u4e8e\u6216\u7b49\u4e8e<\/p>\n\n\n\n
[root@Daniel-R480 ~]# A=3<\/p>\n\n\n\n
[root@Daniel-R480 ~]# B=6<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [$A -eq $B]<\/p>\n\n\n\n
-bash: [3: command not found<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -eq $B]<\/p>\n\n\n\n
-bash: [: missing `]’<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -eq $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
1<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -ne $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
0<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -gt $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
1<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -lt $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
0<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -ge $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
1<\/p>\n\n\n\n
[root@Daniel-R480 ~]# [ $A -le $B ]<\/p>\n\n\n\n
[root@Daniel-R480 ~]# echo $?<\/p>\n\n\n\n
0<\/p>\n\n\n\n
[root@Daniel-R480 ~]#<\/p>\n\n\n\n
5\u3001\u547d\u4ee4\u7684\u95f4\u903b\u8f91\u5173\u7cfb\uff1a<\/p>\n\n\n\n
\uff081\uff09\u903b\u8f91\u4e0e\uff1a &&<\/p>\n\n\n\n
\u7b2c\u4e00\u4e2a\u6761\u4ef6\u4e3a\u5047\u65f6\uff0c\u7b2c\u4e8c\u6761\u4ef6\u4e0d\u7528\u518d\u5224\u65ad\uff0c\u6700\u7ec8\u7ed3\u679c\u5df2\u7ecf\u6709\uff1b<\/p>\n\n\n\n
\u7b2c\u4e00\u4e2a\u6761\u4ef6\u4e3a\u771f\u65f6\uff0c\u7b2c\u4e8c\u6761\u4ef6\u5fc5\u987b\u5f97\u5224\u65ad\uff1b<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user1 &>\/dev\/null && echo “hello student”<\/p>\n\n\n\n
hello student<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user3 &>\/dev\/null && echo “hello student”<\/p>\n\n\n\n
[root@Daniel-R480 ~]# useradd user3<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user3 &>\/dev\/null && echo “hello student”<\/p>\n\n\n\n
hello student<\/p>\n\n\n\n
[root@Daniel-R480 ~]#<\/p>\n\n\n\n
\uff082\uff09\u903b\u8f91\u6216\uff1a ||<\/p>\n\n\n\n
\u5982\u679c\u7528\u6237user6\u4e0d\u5b58\u5728\uff0c\u5c31\u6dfb\u52a0\u7528\u6237user6<\/p>\n\n\n\n
! id user6 && useradd user6<\/p>\n\n\n\n
id user6 || useradd user6<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user6 || useradd user6<\/p>\n\n\n\n
id: user6: no such user<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user6 || useradd user6<\/p>\n\n\n\n
uid=10019(user6) gid=10019(user6) groups=10019(user6)<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user6 || useradd user6<\/p>\n\n\n\n
uid=10019(user6) gid=10019(user6) groups=10019(user6)<\/p>\n\n\n\n
[root@Daniel-R480 ~]# id user6 &>\/dev\/null || useradd user6<\/p>\n\n\n\n
[root@DanielR480 ~]# (id user6 &>\/dev\/null || useradd user6)&& echo ‘hello user6’<\/p>\n\n\n\n
hello user6<\/p>\n\n\n\n
[root@Daniel-R480 ~]#<\/p>\n\n\n\n
\u5982\u679c\/etc\/inittab\u6587\u4ef6\u7684\u884c\u6570\u5927\u4e8e100\uff0c\u5c31\u663e\u793a\u597d\u5927\u7684\u6587\u4ef6\uff1b<\/p>\n\n\n\n
[ `wc -l \/etc\/inittab | cut -d’ ‘ -f1` -gt 100 ] && echo “Large file.”<\/p>\n\n\n\n
6\u3001\u53d8\u91cf\u540d\u79f0\u5b9a\u4e49\u89c4\u8303\uff1a<\/p>\n\n\n\n
1\u3001\u53ea\u80fd\u5305\u542b\u5b57\u6bcd\u3001\u6570\u5b57\u548c\u4e0b\u5212\u7ebf\uff0c\u5e76\u4e14\u4e0d\u80fd\u6570\u5b57\u5f00\u5934\uff1b<\/p>\n\n\n\n
2\u3001\u4e0d\u5e94\u8be5\u8ddf\u7cfb\u7edf\u4e2d\u5df2\u6709\u7684\u73af\u5883\u53d8\u91cf\u91cd\u540d\uff1b<\/p>\n\n\n\n
3\u3001\u6700\u597d\u505a\u5230\u89c1\u540d\u77e5\u4e49\uff1b<\/p>\n\n\n\n
\u5982\u679c\u7528\u6237\u5b58\u5728\uff0c\u5c31\u663e\u793a\u7528\u6237\u5df2\u5b58\u5728\uff1b\u5426\u5219\uff0c\u5c31\u6dfb\u52a0\u6b64\u7528\u6237\uff1b<\/p>\n\n\n\n
id user1 && echo “user1 exists.” || useradd user1<\/p>\n\n\n\n
\u5982\u679c\u7528\u6237\u4e0d\u5b58\u5728\uff0c\u5c31\u6dfb\u52a0\uff1b\u5426\u5219\uff0c\u663e\u793a\u5176\u5df2\u7ecf\u5b58\u5728\uff1b<\/p>\n\n\n\n
! id user1 && useradd user1 || echo “user1 exists.”<\/p>\n\n\n\n
\u5982\u679c\u7528\u6237\u4e0d\u5b58\u5728\uff0c\u6dfb\u52a0\u5e76\u4e14\u7ed9\u5bc6\u7801\uff1b\u5426\u5219\uff0c\u663e\u793a\u5176\u5df2\u7ecf\u5b58\u5728\uff1b<\/p>\n\n\n\n
! id user1 && useradd user1 && echo “user1” | passwd –stdin user1 || echo “user1 exists.”<\/p>\n\n\n\n
\u7ec3\u4e60\uff0c\u5199\u4e00\u4e2a\u811a\u672c\uff0c\u5b8c\u6210\u4ee5\u4e0b\u8981\u6c42\uff1a<\/p>\n\n\n\n
1\u3001\u6dfb\u52a03\u4e2a\u7528\u6237user1, user2, user3\uff1b\u4f46\u8981\u5148\u5224\u65ad\u7528\u6237\u662f\u5426\u5b58\u5728\uff0c\u4e0d\u5b58\u5728\u800c\u540e\u518d\u6dfb\u52a0\uff1b<\/p>\n\n\n\n
2\u3001\u6dfb\u52a0\u5b8c\u6210\u540e\uff0c\u663e\u793a\u4e00\u5171\u6dfb\u52a0\u4e86\u51e0\u4e2a\u7528\u6237\uff1b\u5f53\u7136\uff0c\u4e0d\u80fd\u5305\u62ec\u56e0\u4e3a\u4e8b\u5148\u5b58\u5728\u800c\u6ca1\u6709\u6dfb\u52a0\u7684\uff1b<\/p>\n\n\n\n
3\u3001\u6700\u540e\u663e\u793a\u5f53\u524d\u7cfb\u7edf\u4e0a\u5171\u6709\u591a\u5c11\u4e2a\u7528\u6237\uff1b<\/p>\n\n\n\n
\u7ec3\u4e60\uff0c\u5199\u4e00\u4e2a\u811a\u672c\uff0c\u5b8c\u6210\u4ee5\u4e0b\u8981\u6c42\uff1a<\/p>\n\n\n\n
\u7ed9\u5b9a\u4e00\u4e2a\u7528\u6237\uff1a<\/p>\n\n\n\n
1\u3001\u5982\u679c\u5176UID\u4e3a0\uff0c\u5c31\u663e\u793a\u6b64\u4e3a\u7ba1\u7406\u5458\uff1b<\/p>\n\n\n\n
2\u3001\u5426\u5219\uff0c\u5c31\u663e\u793a\u5176\u4e3a\u666e\u901a\u7528\u6237\uff1b<\/p>\n\n\n\n
\u5982\u679c\u5176UID\u4e3a0 <\/p>\n\n\n\n
\u663e\u793a\u4e3a\u7ba1\u7406\u5458<\/p>\n\n\n\n
\u5426\u5219<\/p>\n\n\n\n
\u663e\u793a\u4e3a\u666e\u901a\u7528\u6237<\/p>\n\n\n\n
NAME=user16<\/p>\n\n\n\n
USERID=`id -u $NAME`<\/p>\n\n\n\n
if [ $USERID -eq 0 ]; then<\/p>\n\n\n\n
echo “Admin”<\/p>\n\n\n\n
else<\/p>\n\n\n\n
echo “common user.”<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
NAME=user16<\/p>\n\n\n\n
if [ `id -u $NAME` -eq 0 ]; then<\/p>\n\n\n\n
echo “Admin”<\/p>\n\n\n\n
else<\/p>\n\n\n\n
echo “common user.”<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
if id $NAME; then<\/p>\n\n\n\n
\u7ec3\u4e60\uff1a\u5199\u4e00\u4e2a\u811a\u672c<\/p>\n\n\n\n
\u5224\u65ad\u5f53\u524d\u7cfb\u7edf\u4e0a\u662f\u5426\u6709\u7528\u6237\u7684\u9ed8\u8ba4shell\u4e3abash\uff1b<\/p>\n\n\n\n
\u5982\u679c\u6709\uff0c\u5c31\u663e\u793a\u6709\u591a\u5c11\u4e2a\u8fd9\u7c7b\u7528\u6237\uff1b\u5426\u5219\uff0c\u5c31\u663e\u793a\u6ca1\u6709\u8fd9\u7c7b\u7528\u6237\uff1b<\/p>\n\n\n\n
#!\/bin\/bash<\/p>\n\n\n\n
#grep “bash$” \/etc\/passwd &> \/dev\/null<\/p>\n\n\n\n
grep “xsh$” \/etc\/passwd &> \/dev\/null<\/p>\n\n\n\n
RETVAL=$?<\/p>\n\n\n\n
if [ $RETVAL -eq 0 ];then<\/p>\n\n\n\n
#COUNT=`grep “bash$” \/etc\/passwd | wc -l`<\/p>\n\n\n\n
#echo $COUNT<\/p>\n\n\n\n
echo `grep “bash$” \/etc\/passwd | wc -l`<\/p>\n\n\n\n
else<\/p>\n\n\n\n
echo “There is no such users.”<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
\u4e0d\u80fd\u5982\u6b64\u6267\u884c\uff1aif grep “bash$” \/etc\/passwd &> \/dev\/null; then<\/p>\n\n\n\n
\u63d0\u793a\uff1a\u201c\u5f15\u7528\u201d\u4e00\u4e2a\u547d\u4ee4\u7684\u6267\u884c\u7ed3\u679c\uff0c\u8981\u4f7f\u7528\u547d\u4ee4\u5f15\u7528\uff1b\u6bd4\u5982: RESAULTS=`wc -l \/etc\/passwd | cut -d: -f1`\uff1b<\/p>\n\n\n\n
\u4f7f\u7528\u4e00\u4e2a\u547d\u4ee4\u7684\u6267\u884c\u72b6\u6001\u7ed3\u679c\uff0c\u8981\u76f4\u63a5\u6267\u884c\u6b64\u547d\u4ee4\uff0c\u4e00\u5b9a\u4e0d\u80fd\u5f15\u7528\uff1b\u6bd4\u5982: if id user1\u4e00\u53e5\u4e2d\u7684id\u547d\u4ee4\u5c31\u4e00\u5b9a\u4e0d\u80fd\u52a0\u5f15\u53f7\uff1b<\/p>\n\n\n\n
\u5982\u679c\u60f3\u628a\u4e00\u4e2a\u547d\u4ee4\u7684\u6267\u884c\u7ed3\u679c\u8d4b\u503c\u7ed9\u67d0\u53d8\u91cf\uff0c\u8981\u4f7f\u7528\u547d\u4ee4\u5f15\u7528\uff0c\u6bd4\u5982USERID=`id -u user1`;<\/p>\n\n\n\n
\u5982\u679c\u60f3\u628a\u4e00\u4e2a\u547d\u4ee4\u7684\u6267\u884c\u72b6\u6001\u7ed3\u679c\u4fdd\u5b58\u4e0b\u6765\uff0c\u5e76\u4f5c\u4e3a\u547d\u4ee4\u6267\u884c\u6210\u529f\u4e0e\u5426\u7684\u5224\u65ad\u6761\u4ef6\uff0c\u5219\u9700\u8981\u5148\u6267\u884c\u6b64\u547d\u4ee4\uff0c\u800c\u540e\u5f15\u7528\u5176\u72b6\u6001\u7ed3\u679c\uff0c\u5982<\/p>\n\n\n\n
id -u user1<\/p>\n\n\n\n
RETVAL=$?<\/p>\n\n\n\n
\u6b64\u53e5\u7edd\u5bf9\u4e0d\u53ef\u4ee5\u5199\u4e3aRETVAL=`id -u user1`\uff1b<\/p>\n\n\n\n
\u7ec3\u4e60\uff1a\u5199\u4e00\u4e2a\u811a\u672c<\/p>\n\n\n\n
\u5224\u65ad\u5f53\u524d\u7cfb\u7edf\u4e0a\u662f\u5426\u6709\u7528\u6237\u7684\u9ed8\u8ba4shell\u4e3abash\uff1b<\/p>\n\n\n\n
\u5982\u679c\u6709\uff0c\u5c31\u663e\u793a\u5176\u4e2d\u4e00\u4e2a\u7684\u7528\u6237\u540d\uff1b\u5426\u5219\uff0c\u5c31\u663e\u793a\u6ca1\u6709\u8fd9\u7c7b\u7528\u6237\uff1b<\/p>\n\n\n\n
#!\/bin\/bash<\/p>\n\n\n\n
grep “bash$” \/etc\/passwd &> \/dev\/null<\/p>\n\n\n\n
#grep “xsh$” \/etc\/passwd &> \/dev\/null<\/p>\n\n\n\n
RETVAL=$?<\/p>\n\n\n\n
if [ $RETVAL -eq 0 ];then<\/p>\n\n\n\n
#COUNT=`grep “bash$” \/etc\/passwd | wc -l`<\/p>\n\n\n\n
#echo $COUNT<\/p>\n\n\n\n
#echo `grep “bash$” \/etc\/passwd | wc -l`<\/p>\n\n\n\n
echo `grep “bash$” \/etc\/passwd | head -1 | cut -d’:’ -f1`<\/p>\n\n\n\n
else<\/p>\n\n\n\n
echo “There is no such users.”<\/p>\n\n\n\n
fi<\/p>\n\n\n\n
fi<\/p>\n","protected":false},"excerpt":{"rendered":"
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