shell script 語法簡易範例

while迴圈

#!/bin/sh
read -r filename
while [ ! -f $filename ]; do
  echo "--> $filename does not exist"
  read -r filename
done
echo "$filename name OK"

until 迴圈

#!/bin/sh
until who | grep dino > /dev/null; do
  sleep 10
done
echo "dino has logged in"

for 迴圈

#!/bin/sh
for foo in *; do
  if [ -f $foo ]; then
     echo "$foo is a file"
  elif [ -d $foo ]; then
     echo "$foo is a directory"
  else
     echo "$foo is not a file, nor directory"
  fi
done

Array[] 

#!/bin/bash
admins=(aaa@example.com bbb@example.com ccc@example.com) 

For Each
for name in ${admins[@]}; do
  mail -s "Log file" $name < $mylog
done

IF判斷式

#!/bin/sh
if grep $1 /etc/passwd > /dev/null
then
  echo "found $1"
else
  echo "didn't find $1"
fi

巢狀IF

#!/bin/sh
if grep $1 /etc/passwd > /dev/null
then
  echo "found $1 in /etc/passwd"
elif grep $1 /etc/greoup > /dev/null
then
  echo "found $1 in /etc/group"
else
  echo "didn't find $1"
fi 

Testing 判斷式
Testing 判斷式通常與if-then-else一起互用, 以便發揮其效果.
先從一個最簡單的例子看起 :

#!/bin/sh
if [ -f /etc/passwd ]; then
   echo "/etc/passwd is a file"
else
   echo "PANIC : /etc/passwd is not a file!!"
fi 

注意: 中括號 []  內每個單元必須以空白分隔 變數與括號也要分開

test     true if ....
[ 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