How to Prepend a String to the Beginning of Each Line in a File

How can I prepend a string to the beginning of each line in a file?

a one-line awk command should do the trick also:

awk '{print "prefix" $0}' file

Add a prefix string to beginning of each line

# If you want to edit the file in-place
sed -i -e 's/^/prefix/' file

# If you want to create a new file
sed -e 's/^/prefix/' file > file.new

If prefix contains /, you can use any other character not in prefix, or
escape the /, so the sed command becomes

's#^#/opt/workdir#'
# or
's/^/\/opt\/workdir/'

How to append a string in beginning of each line in file

str.join inserts a constant string between all elements of the sequence given as argument:

>>> '-'.join(['a', 'b', 'c'])
'a-b-c'

If you want to have it before the first element as well, you can simply use concatenation:

>>> '-' + '-'.join(['a', 'b', 'c'])
'-a-b-c'

... or use a little trick – insert an empty string in the beginning of the sequence:

>>> '-'.join(['', 'a', 'b', 'c'])
'-a-b-c'

In your example, you can use list unpacking to stick with the dense one-liner style:

         file2 = (processed_dateTimeStr.join(["", *z.read(filename).decode("utf-8").splitlines(True)])).encode("utf-8")

How to add a string at the beginning of each line in a file

$ awk '{print "03/06/2012|" $0;}' input.txt > output.txt

Takes about 0.8 seconds for a file with 1.3M lines on some average 2010 hardware.

Append String to each line of .txt file in python?

You can read the lines and put them in a list. Then you open the same file with write mode and write each line with the string you want to append.

filepath = "hole.txt"
with open(filepath) as fp:
    lines = fp.read().splitlines()
with open(filepath, "w") as fp:
    for line in lines:
        print(line + "#", file=fp)

In Bash, how do I add a string after each line in a file?

If your sed allows in place editing via the -i parameter:

sed -e 's/$/string after each line/' -i filename

If not, you have to make a temporary file:

typeset TMP_FILE=$( mktemp )

touch "${TMP_FILE}"
cp -p filename "${TMP_FILE}"
sed -e 's/$/string after each line/' "${TMP_FILE}" > filename

How do I read a file line by line in VB Script?

When in doubt, read the documentation:

filename = "C:\Temp\vblist.txt"

Set fso = CreateObject("Scripting.FileSystemObject")
Set f = fso.OpenTextFile(filename)

Do Until f.AtEndOfStream
  WScript.Echo f.ReadLine
Loop

f.Close

Insert string at the beginning of each line

Python comes with batteries included:

import fileinput
import sys

for line in fileinput.input(['./ampo.txt'], inplace=True):
    sys.stdout.write('EDF {l}'.format(l=line))

Unlike the solutions already posted, this also preserves file permissions.

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