Interpret as fixed string/literal and not regex using sed

Option 1) Escape regexp characters. E.g. sed 's/\$0\.0/0/g' will replace all occurrences of $0.0 with 0.

Option 2) Use perl -p -e in conjunction with quotemeta. E.g. perl -p -e 's/\\./,/gi' will replace all occurrences of . with ,.

You can use option 2 in scripts like this:

SEARCH="C++"
REPLACE="C#"
cat $FILELIST | perl -p -e "s/\\Q$SEARCH\\E/$REPLACE/g" > $NEWLIST

Do you have to use sed? If you're writing a bash script, you can do

#!/bin/bash

pattern='abc'
replace='def'
file=/path/to/file
tmpfile="${TMPDIR:-/tmp}/$( basename "$file" ).$$"

while read -r line
do
  echo "${line//$pattern/$replace}"
done < "$file" > "$tmpfile" && mv "$tmpfile" "$file"

With an older Bourne shell (such as ksh88 or POSIX sh), you may not have that cool ${var/pattern/replace} structure, but you do have ${var#pattern} and ${var%pattern}, which can be used to split the string up and then reassemble it. If you need to do that, you're in for a lot more code - but it's really not too bad.

If you're not in a shell script already, you could pretty easily make the pattern, replace, and filename parameters and just call this. :)

PS: The ${TMPDIR:-/tmp} structure uses $TMPDIR if that's set in your environment, or uses /tmp if the variable isn't set. I like to stick the PID of the current process on the end of the filename in the hopes that it'll be slightly more unique. You should probably use mktemp or similar in the "real world", but this is ok for a quick example, and the mktemp binary isn't always available.

If you don't want to escape your string, you can reach your goal in 2 steps:

1. fgrep the line (getting the line number) you want to replace, and
2. afterwards use sed for replacing this line.

E.g.

#/bin/sh
PATTERN='foo*[)*abc'    # we need it literal
LINENUMBER="$( fgrep -n "$PATTERN" "$FILE" | cut -d':' -f1 )"

NEWSTRING='my new string'
sed -i "${LINENUMBER}s/.*/$NEWSTRING/" "$FILE"

If you're not opposed to Ruby or long lines, you could use this:

alias replace='ruby -e "File.write(ARGV[0], File.read(ARGV[0]).gsub(ARGV[1]) { ARGV[2] })"'

replace test3.txt abc def

This loads the whole file into memory, performs the replacements and saves it back to disk. Should probably not be used for massive files.