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在shell script 中if 條件式的基本語法如下
if [ CONDITION ] then ...... else ...... fi if test CONDITION the ..... else ..... fi
另外在if 條件式中可以利用下面的判斷
[ string1 = string2 ] | string1 and string2 are equal |
[ string1 != string2 ] | string1 and string2 are not equal |
[ string1 \< string2 ] | string1 is lexically less than string2 (e.g. 'a' is less than 'b') |
[ string1 \> string2 ] | string1 is lexically greater than string2 (e.g. 'b' is greater than 'a') |
[ -z string ] | string is zero (e.g. a empty string) |
[ -n string ] | string is nonzero (e.g. a VAR string) |
[ -e file ] | file exists |
[ -f file ] | file is a file |
[ -d file ] | file is a directory |
[ -c file ] | file is a character device |
[ -b file ] | file is a block device |
[ -p file ] | file is a named pipe |
[ -s file ] | file is not empty |
[ -k file ] | file's sticky bit is set |
[ -S file ] | file is a socket |
[ -L file ] | file is a symbolic link |
[ -r file ] | file is readable by user |
[ -w file ] | file is writeable by user |
[ -x file ] | file is executeable by user |
[ -O file ] | file is owner by user |
[ -G file ] | file is group owned by a greoup |
[ -u file ] | file has its set user ID bit set |
[ -g file ] | file has its group user ID bit set |
[ file1 -nt file2 ] | file1 is newer than file2 |
[ file1 -ot file2 ] | file1 is older than file2 |
[ file -ef file2 ] | file1 is another name for file2 |
[ n1 -eq n2 ] | true if integer n1 = integer n2 |
[ n1 -ne n2 ] | true if integer n1 <> n2 |
[ n1 -gt n2 ] | true if n1 > n2 |
[ n1 -ge n2 ] | true if n1 >= n2 |
[ n1 -lt n2 ] | true if n1 < n2 |
[ n1 -le n2 ] | true if n1 <= n2 |
常用的系統符號變數
$# | 參數的數目 |
$* | 代表所有參數 |
$? | Exit status of previous command |
$$ | PID of this shell's process |
$! | PID of the most recently started backgroup job |
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