windows – 使用批处理文件插入字符串

field1      field2           field3
AAAAA       BBBBB            CCCCC
DDDDD                        EEEEE
FFFFF                        
GGGGG       HHHHH

field1      field2           field3
AAAAA       BBBBB            CCCCC
DDDDD       NULL             EEEEE
FFFFF       NULL             NULL    
GGGGG       HHHHH            NULL

@echo off

set line= 
for /F in (input.txt)do
if "!line:~12" equ " " 
write "NULL"   >> (i am not sure whether this work)

if "!line:~29" equ " "
write "NULL"  

echo .>> output.txt

正如所承诺的,这是Python的解决方案.使用Python 3.x或Python 2.7,该程序可以正常工作.如果您对编程非常陌生,我建议使用Python 3.x,因为我觉得它更容易学习.你可以从这里免费获得Python： http://python.org/download/

最新版本的Python是版本3.2.3;我建议你明白.

将Python代码保存在名为add_null.py的文件中,并使用以下命令运行它：

python add_null.py input_file.txt output_file.txt

代码,有很多评论：

# import brings in "modules" which contain extra code we can use.
# The "sys" module has useful system stuff,including the way we can get
# command-line arguments.
import sys

# sys.argv is an array of command-line arguments.  We expect 3 arguments:
# the name of this program (which we don't care about),the input file
# name,and the output file name.
if len(sys.argv) != 3:
    # If we didn't get the right number of arguments,print a message and exit.
    print("Usage: python add_null.py <input_file> <output_file>")
    sys.exit(1)

# Unpack the arguments into variables.  Use '_' for any argument we don't
# care about.
_,input_file,output_file = sys.argv


# Define a function we will use later.  It takes two arguments,a string
# and a width.
def s_padded(s,width):
    if len(s) >= width:
        # if it is already wide enough,return it unchanged
        return s
    # Not wide enough!  Figure out how many spaces we need to pad it.
    len_padding = width - len(s)
    # Return string with spaces appended.  Use the Python "string repetition"
    # feature to repeat a single space,len_padding times.
    return s + ' ' * len_padding


# These are the column numbers we will use for splitting,plus a width.
# Numbers put together like this,in parentheses and separated by commas,# are called "tuples" in Python.  These tuples are: (low,high,width)
# The low and high numbers will be used for ranges,where we do use the
# low number but we stop just before the high number.  So the first pair
# will get column 0 through column 11,but will not actually get column 12.
# We use 999 to mean "the end of the line"; if the line is too short,it will
# not be an error.  In Python "slicing",if the full slice can't be done,you
# just get however much can be done.
#
# If you want to cut off the end of lines that are too long,change 999 to
# the maximum length you want the line ever to have.  Longer than
# that will be chopped short by the "slicing".
#
# So,this tells the program where the start and end of each column is,and
# the expected width of the column.  For the last column,the width is 0,# so if the last column is a bit short no padding will be added.  If you want
# to make sure that the lines are all exactly the same length,change the
# 0 to the width you want for the last column.
columns = [ (0,12,12),(12,29,17),(29,999,0) ]
num_columns = len(columns)

# Open input and output files in text mode.
# Use a "with" statement,which will close the files when we are done.
with open(input_file,"rt") as in_f,open(output_file,"wt") as out_f:
    # read the first line that has the field headings
    line = in_f.readline()
    # write that line to the output,unchanged
    out_f.write(line)

    # now handle each input line from input file,one at a time
    for line in in_f:
        # strip off only the line ending
        line = line.rstrip('n')

        # start with an empty output line string,and append to it
        output_line = ''
        # handle each column in turn
        for i in range(num_columns):
            # unpack the tuple into convenient variables
            low,width = columns[i]
            # use "slicing" to get the columns we want
            field = line[low:high]
            # Strip removes spaces and tabs; check to see if anything is left.
            if not field.strip():
                # Nothing was left after spaces removed,so put "NULL".
                field = "NULL"

            # Append field to output_line.  field is either the original
            # field,unchanged,or else it is a "NULL".  Either way,# append it.  Make sure it is the right width.
            output_line += s_padded(field,width)

        # Add a line ending to the output line.
        output_line += "n"
        # Write the output line to the output file.
        out_f.write(output_line)

运行此程序的输出：

field1      field2           field3
AAAAA       BBBBB            CCCCC
DDDDD       NULL             EEEEE
FFFFF       NULL             NULL
GGGGG       HHHHH            NULL