Find and Replace Inside a Text File from a Bash Command

Question

What's the simplest way to do a find and replace for a given input string, say abc, and replace with another string, say XYZ in file /tmp/file.txt?

I am writting an app and using IronPython to execute commands through SSH — but I don't know Unix that well and don't know what to look for.

I have heard that Bash, apart from being a command line interface, can be a very powerful scripting language. So, if this is true, I assume you can perform actions like these.

Can I do it with bash, and what's the simplest (one line) script to achieve my goal?

Answer 1

The easiest way is to use sed (or perl):

sed -i -e 's/abc/XYZ/g' /tmp/file.txt

Which will invoke sed to do an in-place edit due to the -i option. This can be called from bash.

If you really really want to use just bash, then the following can work:

while IFS='' read -r a; do
    echo "${a//abc/XYZ}"
done < /tmp/file.txt > /tmp/file.txt.t
mv /tmp/file.txt{.t,}

This loops over each line, doing a substitution, and writing to a temporary file (don't want to clobber the input). The move at the end just moves temporary to the original name. (For robustness and security, the temporary file name should not be static or predictable, but let's not go there.)

For Mac users:

sed -i '' 's/abc/XYZ/g' /tmp/file.txt

(See the comment below why)

Answer 2

File manipulation isn't normally done by Bash, but by programs invoked by Bash, e.g.:

perl -pi -e 's/abc/XYZ/g' /tmp/file.txt

The -i flag tells it to do an in-place replacement.

See man perlrun for more details, including how to take a backup of the original file.

Answer 3

I was surprised when I stumbled over this...

There is a replace command which ships with the "mysql-server" package, so if you have installed it try it out:

# replace string abc to XYZ in files
replace "abc" "XYZ" -- file.txt file2.txt file3.txt

# or pipe an echo to replace
echo "abcdef" |replace "abc" "XYZ"

See man replace for more on this.

Answer 4

This is an old post but for anyone wanting to use variables as @centurian said the single quotes mean nothing will be expanded.

A simple way to get variables in is to do string concatenation since this is done by juxtaposition in bash the following should work:

sed -i -e "s/$var1/$var2/g" /tmp/file.txt

Answer 5

Bash, like other shells, is just a tool for coordinating other commands. Typically you would try to use standard UNIX commands, but you can of course use Bash to invoke anything, including your own compiled programs, other shell scripts, Python and Perl scripts etc.

In this case, there are a couple of ways to do it.

If you want to read a file, and write it to another file, doing search/replace as you go, use sed:

    sed 's/abc/XYZ/g' <infile >outfile

If you want to edit the file in place (as if opening the file in an editor, editing it, then saving it) supply instructions to the line editor 'ex'

    echo "%s/abc/XYZ/g
    w
    q
    " | ex file

Example is like vi without the fullscreen mode. You can give it the same commands you would at vi's : prompt.

Answer 6

I found this thread among others and I agree it contains the most complete answers so I'm adding mine too:

1. sed and ed are so useful...by hand. Look at this code from @Johnny:

   sed -i -e 's/abc/XYZ/g' /tmp/file.txt
   

2. When my restriction is to use it in a shell script, no variable can be used inside in place of "abc" or "XYZ". The BashFAQ seems to agree with what I understand at least. So, I can't use:

   x='abc'
   y='XYZ'
   sed -i -e 's/$x/$y/g' /tmp/file.txt
   #or,
   sed -i -e "s/$x/$y/g" /tmp/file.txt
   

   but, what can we do? As, @Johnny said use a while read... but, unfortunately that's not the end of the story. The following worked well with me:

   #edit user's virtual domain
   result=
   #if nullglob is set then, unset it temporarily
   is_nullglob=$( shopt -s | egrep -i '*nullglob' )
   if [[ is_nullglob ]]; then
      shopt -u nullglob
   fi
   while IFS= read -r line; do
      line="${line//'<servername>'/$server}"
      line="${line//'<serveralias>'/$alias}"
      line="${line//'<user>'/$user}"
      line="${line//'<group>'/$group}"
      result="$result""$line"'\n'
   done < $tmp
   echo -e $result > $tmp
   #if nullglob was set then, re-enable it
   if [[ is_nullglob ]]; then
      shopt -s nullglob
   fi
   #move user's virtual domain to Apache 2 domain directory
   ......
   

3. As one can see if nullglob is set then, it behaves strangely when there is a string containing a * as in:

   <VirtualHost *:80>
    ServerName www.example.com
   

   which becomes

   <VirtualHost ServerName www.example.com
   

   there is no ending angle bracket and Apache2 can't even load.

4. This kind of parsing should be slower than one-hit search and replace but, as you already saw, there are four variables for four different search patterns working out of one parse cycle.

The most suitable solution I can think of with the given assumptions of the problem.

Answer 7

You can use sed:

sed -i 's/abc/XYZ/gi' /tmp/file.txt

You can use find and sed if you don't know your filename:

find ./ -type f -exec sed -i 's/abc/XYZ/gi' {} \;

Find and replace in all Python files:

find ./ -iname "*.py" -type f -exec sed -i 's/abc/XYZ/gi' {} \;

Answer 8

Be careful if you replace URLs with "/" character.

An example of how to do it:

sed -i "s%http://domain.com%http://www.domain.com/folder/%g" "test.txt"

Extracted from: http://www.sysadmit.com/2015/07/linux-reemplazar-texto-en-archivos-con-sed.html

Answer 9

If the file you are working on is not so big, and temporarily storing it in a variable is no problem, then you can use Bash string substitution on the whole file at once - there's no need to go over it line by line:

file_contents=$(</tmp/file.txt)
echo "${file_contents//abc/XYZ}" > /tmp/file.txt

The whole file contents will be treated as one long string, including linebreaks.

XYZ can be a variable eg $replacement, and one advantage of not using sed here is that you need not be concerned that the search or replace string might contain the sed pattern delimiter character (usually, but not necessarily, /). A disadvantage is not being able to use regular expressions or any of sed's more sophisticated operations.

Answer 10

You may also use the ed command to do in-file search and replace:

# delete all lines matching foobar 
ed -s test.txt <<< $'g/foobar/d\nw' 

See more in "Editing files via scripts with ed".

Answer 11

To edit text in the file non-interactively, you need in-place text editor such as vim.

Here is simple example how to use it from the command line:

vim -esnc '%s/foo/bar/g|:wq' file.txt

This is equivalent to @slim answer of ex editor which is basically the same thing.

Here are few ex practical examples.

Replacing text foo with bar in the file:

ex -s +%s/foo/bar/ge -cwq file.txt

Removing trailing whitespaces for multiple files:

ex +'bufdo!%s/\s\+$//e' -cxa *.txt

Troubleshooting (when terminal is stuck):

• Add -V1 param to show verbose messages.
• Force quit by: -cwq!.

See also:

• How to edit files non-interactively (e.g. in pipeline)? at Vi SE

Answer 12

Try the following shell command:

find ./  -type f -name "file*.txt" | xargs sed -i -e 's/abc/xyz/g'

Answer 13

You can use python within the bash script too. I didn't have much success with some of the top answers here, and found this to work without the need for loops:

#!/bin/bash
python
filetosearch = '/home/ubuntu/ip_table.txt'
texttoreplace = 'tcp443'
texttoinsert = 'udp1194'

s = open(filetosearch).read()
s = s.replace(texttoreplace, texttoinsert)
f = open(filetosearch, 'w')
f.write(s)
f.close()
quit()

Answer 14

Simplest way to replace multiple text in a file using sed command

Command -

sed -i 's#a/b/c#D/E#g;s#/x/y/z#D:/X#g;' filename

In the above command s#a/b/c#D/E#g where I am replacing a/b/c with D/E and then after the ; we again doing the same thing

Answer 15

You can use rpl command. For example you want to change domain name in whole php project.

rpl -ivRpd -x'.php' 'old.domain.name' 'new.domain.name' ./path_to_your_project_folder/  

This is not clear bash of cause, but it's a very quick and usefull. :)

Answer 16

For MAC users in case you don't read the comments :)

As mentioned by @Austin, if you get the Invalid command code error

For the in-place replacements BSD sed requires a file extension after the -i flag to save to a backup file with given extension.

sed -i '.bak' 's/find/replace' /file.txt

You can use '' empty string if you want to skip backup.

sed -i '' 's/find/replace' /file.txt

All merit to @Austin

Answer 17

In case of doing changes in multiple files together we can do in a single line as:-

user_name='whoami'
for file in file1.txt file2.txt file3.txt; do sed -i -e 's/default_user/${user_name}/g' $file; done

Added if in case could be useful.