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 writing 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. 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?

Masse

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. The /g flag for sed's s command says to replace globally, i.e. do not substitute only the first occurrence on each input line. This can be called from Bash.

(The -i option is not standard. On BSD-based platforms, including MacOS, you need an explicit option argument -i ''.)

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 mv at the end just moves the temporary file to the original name. (For robustness and security, the temporary file name should not be static or predictable, but let's not go there.)

This uses a Bash-only parameter expansion to perform a replacement on the variable's value.

Pledgee

Except that invoking mv is pretty much as 'non Bash' as using sed. I nearly said the same of echo, but it's a shell builtin. – Haugh

The -i argument for sed doesn't exist for Solaris (and I would think some other implementations) however, so keep that in mind. Just spent several minutes figuring that out... – Midvictorian

Note to self: about regular expression of sed: s/..../..../ - Substitute and /g - Global – Standoff

Ps: For me, this variant is 1/3 faster: for a in `cat hosts.txt` ; do echo ${a//abc/XYZ} ; done > hosts.txt.t) – Roane

Note for Mac users who get an invalid command code C error... For in-place replacements, BSD sed requires a file extension after the -i flag because it saves a backup file with the given extension. For example: sed -i '.bak' 's/find/replace/' /file.txt You can skip the backup by using an empty string like so: sed -i '' 's/find/replace/' /file.txt – Tormentil

Tip: If you want case insensitive repalce use s/abc/XYZ/gi – Electrocautery

Anyway to disable the RegEx functionality and use them as only strings (Replace only the whole word)? – Crosse

@Crosse I'm not sure if I understood your question, as regex can replace whole words only. Simply type a word between / / slash characters. You must escape some characters with backslash, such as $, *, ", ', \. – Envenom

@Crosse Some sed dialects ellow you to put word anchors s/\bfoo\b/bar/ to only replace foo if it is surrounded by word boundaries. However, the Perlism \b is not standard. Some older regex englines support s/\<foo\>/bar/ – Plangent

@BorisD.Teoharov The i flag is nonstandard; but if your sed has it, cool. Perl should have this flag in every version but is itself nonstandard. – Plangent

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.

Brannon

The purist in me says you can't be sure Perl will be available on the system. But that's very seldom the case nowadays. Perhaps I'm showing my age. – Haugh

Can you show a more complex example. Something like replacing "chdir /blah" with "chdir /blah2". I tried perl -pi -e 's/chdir (?:\\/[\\w\\.\\-]+)+/chdir blah/g' text, but I keep getting an error with Having no space between pattern and following word is deprecated at -e line 1. Unmatched ( in regex; marked by <-- HERE in m/(chdir)( )( <-- HERE ?:\\/ at -e line 1. – Rift

@Rift Check this answer: https://mcmap.net/q/55135/-how-to-replace-a-path-with-another-path-in-sed-duplicate – Impermanent

Why use Perl in this case when it's only function is to wrap a language around sed? – Malayopolynesian

@EdwinBuck some sed implementations don't support in-place editing. – Brannon

perl command options explained – Newly

Answer 3

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

Donkey

I use this in a file:sed "s/\"$li\"/- [x]\"\${li:5}\"/" $dat ang get sed unterminated `s' command – Garlaand

Problem solved, well, ... $li comes from a file line, so there is e.g. \n and the error is there. So either awk or another language like python comes. – Garlaand

Answer 4

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.

Tirzah

Two things are possible here: a) replace is a useful independent tool and the MySQL folks should release it separately and depend on it b) replace requires some bit of MySQL o_O Either way, installing mysql-server to get replace would be the wrong thing to do :) – Primal

only works for mac? in my ubuntu I centos that command does not exist – Antitoxin

That's because you don't have mysql-server package installed. As pointed by @rayro, replace is part of it. – Hereinbefore

"Warning: replace is deprecated and will be removed in a future version." – Threedimensional

As of 2018, it is included in the MariaDB package for Ubuntu. – Xenolith

Not as powerful, but I have a simple "script" here that does the same in case downloading a MySQL or MariaDB is overkill: gist.github.com/neuro-sys/3bf00b6cf28a93e07e44 – Davon

Be careful not to run the REPLACE command on Windows! On Windows the REPLACE command is for a fast replication of files. Not relevant to this discussion. – Jaggery

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.

Haugh

@awattar Just do them one at a time in a for loop. – Haugh

Is there an option to use it together with globbing as a one liner? – Jar

Not as far as I know. for f in report*.txt; do echo "%s/abc/XYZ/g \n w \n q \n" | ex file; done is clean and simple. Why put functionality into ex that the shell already has? – Haugh

(Or, if your problem outgrows the shell, use Python/Perl/whatever) – Haugh

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.

Unsaddle

In your (2) -- you can do sed -e "s/$x/$y/", and it will work. Not the double quotes. It can get seriously confusing if the strings in the variables themselves contain characters with special meaning. For example if x="/" or x="\". When you hit these issues, it probably means you should stop trying to use the shell for this job. – Haugh

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' {} \;

Everick

-i isn't "ignore case", it's -i[SUFFIX], --in-place[=SUFFIX] (edit files in place (makes backup if SUFFIX supplied)) – Benthamism

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

Defy

Answer 9

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".

Ain

This solution is independent from GNU/FreeBSD (Mac OSX) incompatibilities (unlike sed -i <pattern> <filename>). Very nice! – Krystinakrystle

Answer 10

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.

Plumule

Any tips for using this with tab characters? For some reason my script doesn't find anything with tabs after changing from sed with lots of escaping to this method. – Dissimilitude

If you want to put a tab in the string you're replacing, you can do so with Bash's "dollared single quotes" syntax, so a tab is represented by $'\t', and you can do $ echo 'tab'$'\t''separated' > testfile; $ file_contents=$(<testfile); $ echo "${file_contents//$'\t'/TAB}"; tabTABseparated ` – Plumule

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

Deborahdeborath

Wanted to do the replacements interactively. Hence tried "vim -esnc '%s/foo/bar/gc|:wq' file.txt". But the terminal is stuck now. How shall we make the replacements interactively without the bash shell behaving weirdly. – Gunning

To debug, add -V1, to force quit, use wq!. – Deborahdeborath

Answer 12

Try the following shell command:

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

Bullhorn

This is an excellent answer to "how do I accidentally all the files in all subdirectories, too" but that does not seem to be what is asked here. – Plangent

This syntax won't work for BSD version of sed, use sed -i'' instead. – Deborahdeborath

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()

Vermiculate

Answer 14

You can use the rpl command; this is an optional third-party tool (source at https://github.com/rrthomas/rpl/). For example, if you want to change a domain name in a whole PHP project:

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

This is not pure Bash of cause, but it's a very quick and useful.

Thou

This is easily done with standard tools as well. The sed solutions on this page show how to do it in one directory (though you need sed -i which is also nonstandard for most of them); just plug in into find . -type f -name '*.php' -exec ... \; to replace recursively in all *.php files in a directory tree. – Plangent

Answer 15

Simplest way to replace multiple text in a file using the sed 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 I am replacing a/b/c with D/E and then after the ; we are again doing the same thing with x/y/z and D:/X

Brawner

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

Encomium

Answer 17

Open file using vim editor. In command mode

:%s/abc/xyz/g 

This is the simplest

Increment

Dubious. The user then separately has to learn how to quit Vim. – Plangent

Answer 18

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.

Kathernkatheryn

The loop does nothing useful; sed natively knows how to process multiple files. Also, you have a bug: When to wrap quotes around a shell variable? – Plangent