将dos控制字符^M替换掉;

  # IN unix ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format)
     sed 's/^M$//'              # in bash/tcsh, press Ctrl-V then Ctrl-M
     sed 's/.$//'               # assumes that all lines end with CR/LF 
     sed 's/\x0D$//'            # gsed 3.02.80, but top script is easier 
  
  # IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format 
     sed "s/$/`echo -e \\\r`/"  # command line under ksh 
     sed 's/$'"/`echo \\\r`/"   # command line under bash 
     sed "s/$/`echo \\\r`/"     # command line under zsh 
     sed 's/$/\r/'              # gsed 3.02.80

  # IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format 
     sed "s/$//"                # method 1 
     sed -n p                   # method 2

  # IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format 
  # Cannot be done with DOS versions of sed. Use "tr" instead. 
     tr -d \r outfile  # GNU tr version 1.22 or higher

Example:删除文件中的所有空行和由空格组成的行;
$cat ifile|sed '/^$/d'|sed '/^[[:space:]]*$/d'    # method 1
$cat ifile|sed -e '/^$/d' -e '/^[[:space:]]*$/d'  # method 2