Find and Replace Inside a Text File from a Bash Command

Ash_11194 0
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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?

ironpython scripting bash replace
17 Answers

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)

user_610970

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.

Alnitak_67820

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.

user_75120

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".

Admin1

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

user_80718570

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

user_67928290

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.

user_101258920
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