shell中if用法.docx

第一部分 If的用法第一种 iflistthen dosomethinghere fi 当list表述返回值为True(0)时，将会执行dosomethinghere。#!/bin/sh myPath=/var/log/httpd/ myFile=/var /log/httpd/access.log 1. 是否存在并且是否具有可执行权限 #这里的-x 参数判断$myPathif ! -x $myPath; then mkdir $myPath fi 2. 目录是否存在 #这里的-d 参数判断$myPath是否存在 if ! -d $myPath; then mkdir $myPath fi 3. 文件是否存在 #这里的-f参数判断$myFile是否存在 if ! -f $myFile ; then touch $myFile fi 4. 变量是否有值#其他参数还有-n,-n是判断一个变量是否是否有值 if ! -n $myVar ; then echo $myVar is empty exit 0 fi 5. 两个变量判断是否相等 if $var1 = $var2 ; then echo $var1 eq $var2 else echo $var1 not eq $var2 fi6. 比较数字的大小if $df -gt 50 then $df diskalertelseexitfi7. 字符串和数字比较大小if (d = 0) if $D -eq 0 ; then if (d != 0) if $D -ne 0 ; then if (d 0) if $D -gt 0 ; then if (d 0) if $D -lt 0 ; then if (d = 0) if $D -ge 0 ; then 字符串比较 if (strcmp(str,”abc”)=0) if $STR != abc ; then8. If其他用法shell脚本中判断环境变量是否存在2007-09-12 20:25if ! -d $JAVA_HOME then echo JAVA_HOME not set!else echo JAVA_HOME: $JAVA_HOMEfi更紧凑的写法 -n $JAVA_HOME &echo exist|echo No exist注意-d和-n是不同的，前者判断目录是否存在，后者判断String是否不为空-a file True if file exists. -b file True if file exists and is a block special file. -c file True if file exists and is a character special file. -d file True if file exists and 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 exists and is set-group-id. -h file True if file exists and is a symbolic link. -k file True if file exists and its sticky bit is set. -p file True if file exists and is a named pipe (FIFO). -r file True if file exists and is readable. -s file True if file exists and has a size greater than zero. -t fd True if file descriptor fd is open and refers to a terminal. -u file True if file exists and its set-user-id bit is set. -w file True if file exists and is writable. -x file True if file exists and is executable. -O file True if file exists and is owned by the effective user id. -G file True if file exists and is owned by the effective group id. -L file True if file exists and is a symbolic link. -S file True if file exists and is a socket. -N file True if file exists and has been modified since it was last read. file1 -nt file2 True if file1 is newer (according to modification date) than file2. file1 -ot file2 True if file1 is older than file2. file1 -ef file2 True if file1 and file2 have the same device and inode numbers. -o optname True if shell option optname is enabled. See the list of options under the description of the -o option to the set builtin below. -z string True if the length of string is zero. -n string string True if the length of string is non-zero. string1 = string2 True if the strings are equal. = may be used in place of =. string1 != string2 True if the strings are not equal. string1 string2 True if string1 sorts after string2 lexicographi? cally in the current locale. arg1 OP arg2 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers.第二部分 shell脚本1. 删除相同内容的文件for file in * #遍历文件do if ! -f $file #如果文件存在的话,因为有的文件可能被剔除了. then echo $file not exist else for i in * do if $file != $i #如果文件名不同 then if cmp -s $file $i then mv $i ./same/ fi fi done mv $file ./unique/ fidone我一共处理4000多个文件,运行的挺慢的,用了1天零2夜才处理完,我汗,竟剔出了近2000,我再汗.为了提高效率,后来考虑只对文件大小相同的文件才进行比较.脚本如下:for file in * #遍历文件do if ! -f $file #如果文件存在的话,因为有的文件可能被剔除了. then echo $file not exist else leno=ls -l $file | awk print #使用ls和awk提出文件大小 for i in * do leni=ls -l $i | awk print if $file != $i -a $leno = $leni #如果文件名不同,并且文件大小相同 then if cmp -s $file $i then mv $i ./same/ fi fi do