Ubuntu – sed command replace text with ‘ character

sed

I have an very big sql file that I cant open in a gui editor. I need to replace the string
'user1'@'localhost' (note the ` character) by 'user2'@'localhost' but i am having troubles finding the right syntax for sed command.

I can get the strings to replace correcly using the following grep command:

grep -w 'user1`@`localhost'

Any help please?
Thank you.

Best Answer

I thought of a more general solution than as your question asks for.

Let's imagine you need to find a string based on your regular expression search criteria. You'd like to replace only a part of it, and leave the other matching parts unchanged.

To demonstrate with an example:

echo "'some-name'@'some-host'" | sed -r "s/(')([^']+)('@'[^']*')/\1user2\3/g"

will display:

'user2'@'some-host'

The sed command performs the replacement by using the s/search-regexp/replacement/g syntax. In our case:

(') matches the first single quote. This is trivial, but could be more complex. It represents the part of the string before the replacement. sed assigns the value of this sub-expression to the special variable \1.
([^']+) matches the user name. Basically any character starting from the previous position that is not a quote. sed assigns the value of this sub-expression to the special variable \2.
('@'[^']*') matches the '@'host-name' part. Similarly to the previous sub-expression, a quote, a @, a quote again and any character that is not a quote and then a quote at the end. sed assigns the value of this sub-expression to the special variable \3.

The replacement part will replace anything that matched the search-regexp. By using the variables shown above, we can replace the user name and leave the other regions intact. \1 + your new user name + \3 will produce the desired result. Thus:

\1user2\3

Results in:

Whatever contents the first sub-expression has, (it is a single quote)
followed by the string "user2", (note \2 is intentionally not used, because we replace the user name)
and finally the contents of the 3rd sub-expression (which is a '@ and the host name in quotes).

If you cat your script file and pipe it to the sed command, you should get the desired result.

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Ubuntu – sed replace text containing new line

How about

search for #ServerRoot "/etc/apache2"
if found, read and append the next line into sed's pattern space
search the appended pattern space for an empty line after the newline, and substitute ServerName localhost for that

Putting that together,

sed -i '\|#ServerRoot "/etc/apache2"| {N;s|\n$|\nServerName localhost|}' /etc/apache2/apache2.conf

In case the 'empty' line actually contains whitespace, you could modify that to

sed -i '\|#ServerRoot "/etc/apache2"| {N;s|\n\s*$|\nServerName localhost|}' /etc/apache2/apache2.conf

Ubuntu – multiple file text replace with sed

You can loop through the file using while ... do loop:

$ while read i; do printf "Current line: %s\n" "$i"; done < target_files_list.txt

In your case you should replace printf ... with sed command you want.

$ while read i; do sed -i -- 's/SOME_TEXT/SOME_TEXT_TO_REPLACE/g' "$i"; done < target_files_list.txt

However, notice that you can achieve what you want using only find:

$ find /path/to/files/ -name "target_text_file" -exec sed -i -- 's/SOME_TEXT/SOME_TEXT_TO_REPLACE/g' {} \;

You can read more about -exec option by running man find | less '+/-exec ':

   -exec command ;

          Execute command; true if 0 status is returned.  All
          following arguments to find are taken to be arguments to
          the command until an argument consisting of `;' is
          encountered.  The string `{}' is replaced by the current
          file name being processed everywhere it occurs in the
          arguments to the command, not just in arguments where it
          is alone, as in some versions of find.  Both of these
          constructions might need to be escaped (with a `\') or
          quoted to protect them from expansion by the shell.  See
          the EXAMPLES section for examples of the use of the
          -exec option.  The specified command is run once for
          each matched file.  The command is executed in the
          starting directory.  There are unavoidable security
          problems surrounding use of the -exec action; you should
          use the -execdir option instead.

EDIT:

As correctly noted by users terdon and dessert in the comments it's necessary to use -r with read because it will correctly handle backslashes. It's also reported by shellcheck:

$ cat << EOF >> do.sh
#!/usr/bin/env sh
while read i; do printf "$i\n"; done < target_files_list.txt
EOF
$ ~/.cabal/bin/shellcheck do.sh

In do.sh line 2:
while read i; do printf "\n"; done < target_files_list.txt
      ^-- SC2162: read without -r will mangle backslashes.

So it should be:

$ while read -r i; do sed -i -- 's/SOME_TEXT/SOME_TEXT_TO_REPLACE/g' "$i"; done < target_files_list.txt

Best Answer

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Ubuntu – sed replace text containing new line

Ubuntu – multiple file text replace with sed

EDIT:

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