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/'

awk '$0="prefix"$0' file > new_file

In awk the default action is '{print $0}' (i.e. print the whole line), so the above is equivalent to:

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

With Perl (in place replacement):

perl -pi 's/^/prefix/' file

Here is a hightly readable oneliner solution using the ts command from moreutils

$ cat file | ts prefix | tr -d ' '

And how it's derived step by step:

# Step 0. create the file

$ cat file
line1
line2
line3

# Step 1. add prefix to the beginning of each line

$ cat file | ts prefix
prefix line1
prefix line2
prefix line3

# Step 2. remove spaces in the middle

$ cat file | ts prefix | tr -d ' '
prefixline1
prefixline2
prefixline3

Using & (the whole part of the input that was matched by the pattern”):

cat in.txt | sed -e "s/.*/prefix&/" > out.txt

OR using back references:

cat in.txt | sed -e "s/\(.*\)/prefix\1/" > out.txt

Using the shell:

#!/bin/bash
prefix="something"
file="file"
while read -r line
do
 echo "${prefix}$line"
done <$file > newfile
mv newfile $file

Using ed:

ed infile <<'EOE'
,s/^/prefix/
wq
EOE

This substitutes, for each line (,), the beginning of the line (^) with prefix. wq saves and exits.

If the replacement string contains a slash, we can use a different delimiter for s instead:

ed infile <<'EOE'
,s#^#/opt/workdir/#
wq
EOE

I've quoted the here-doc delimiter EOE ("end of ed") to prevent parameter expansion. In this example, it would work unquoted as well, but it's good practice to prevent surprises if you ever have a $ in your ed script.

1. You can also achieve this using the backreference technique

   sed -i.bak 's/\(.*\)/prefix\1/' foo.txt
   

2. You can also use with awk like this

   awk '{print "prefix"$0}' foo.txt > tmp && mv tmp foo.txt
   

Using Pythonize (pz):

pz '"preix"+s' <filename

Simple solution using a for loop on the command line with bash:

for i in $(cat yourfile.txt); do echo "prefix$i"; done

Save the output to a file:

for i in $(cat yourfile.txt); do echo "prefix$i"; done > yourfilewithprefixes.txt

You can do it using AWK

echo example| awk '{print "prefix"$0}'

or

awk '{print "prefix"$0}' file.txt > output.txt

For suffix: awk '{print $0"suffix"}'

For prefix and suffix: awk '{print "prefix"$0"suffix"}'

For people on BSD/OSX systems there's utility called lam, short for laminate. lam -s prefix file will do what you want. I use it in pipelines, eg:

find -type f -exec lam -s "{}: " "{}" \; | fzf

...which will find all files, exec lam on each of them, giving each file a prefix of its own filename. (And pump the output to fzf for searching.)

If you need to prepend a text at the beginning of each line that has a certain string, try following. In the following example, I am adding # at the beginning of each line that has the word "rock" in it.

sed -i -e 's/^.*rock.*/#&/' file_name

SETLOCAL ENABLEDELAYEDEXPANSION

YourPrefix=blabla

YourPath=C:\path

for /f "tokens=*" %%a in (!YourPath!\longfile.csv)     do (echo !YourPrefix!%%a) >> !YourPath!\Archive\output.csv