Interpret as fixed string/literal and not regex using sed

Question

For grep there's a fixed string option, -F (fgrep) to turn off regex interpretation of the search string. Is there a similar facility for sed? I couldn't find anything in the man. A recommendation of another gnu/linux tool would also be fine.

I'm using sed for the find and replace functionality: sed -i "s/abc/def/g"

Answer 1

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.

Answer 2

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

Answer 3

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.

Answer 4

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"

Answer 5

You can do this in two lines of bash code if you're OK with reading the whole file into memory. This is quite flexible -- the pattern and replacement can contain newlines to match across lines if needed. It also preserves any trailing newline or lack thereof, which a simple loop with read does not.

mapfile -d '' < file
printf '%s' "${MAPFILE//"$pat"/"$rep"}" > file

For completeness, if the file can contain null bytes (\0), we need to extend the above, and it becomes

mapfile -d '' < <(cat file; printf '\0')
last=${MAPFILE[-1]}; unset "MAPFILE[-1]"
printf '%s\0' "${MAPFILE[@]//"$pat"/"$rep"}" > file
printf '%s' "${last//"$pat"/"$rep"}" >> file

Answer 6

perl -i.orig -pse  'while (($i = index($_,$s)) >= 0) { substr($_,$i,length($s), $r)}'--\ 
     -s='$_REQUEST['\'old\'']' -r='$_REQUEST['\'new\'']' sample.txt

• -i.orig in-place modification with backup.
• -p print lines from the input file by default
• -s enable rudimentary parsing of command line arguments
• -e run this script
• index($_,$s) search for the $s string
• substr($_,$i,length($s), $r) replace the string
• while (($i = index($_,$s)) >= 0) repeat until
• -- end of perl parameters
• -s='$_REQUEST['\'old\'']', -r='$_REQUEST['\'new\'']' - set $s,$r

You still need to "escape" ' chars but the rest should be straight forward.

Note: this started as an answer to How to pass special character string to sed hence the $_REQUEST['old'] strings, however this question is a bit more appropriately formulated.

Answer 7

You should be using replace instead of sed.

From the man page:

   The replace utility program changes strings in place in files or on the
   standard input.

   Invoke replace in one of the following ways:

       shell> replace from to [from to] ... -- file_name [file_name] ...
       shell> replace from to [from to] ... < file_name

   from represents a string to look for and to represents its replacement.
   There can be one or more pairs of strings.