Match with fixed string in sed - linux

Question

I have to use sed to match with a fixed string.
I have a pseudo database in a file like:
key\x0value
keyyy\x0value
If I whish to get the first line only if i use as argument "key" and not "ey" for example.
* Match with key : "key"
* Do not match : "k", "ke.", "ey", ... : No regex, no partial search, only "key"
I cannot use awk and the string MUST contain a \x0 at the end of the key.
It seems that I cannot use grep neither because it doesn't handle the \x0 or \0
The problem is that I cannot both ask to match /^key\x0/ and do not interpret key with a regex.
Finaly, my sript will take only ONE argument : the EXACT KEY TO MATCH.

Answer 1

sed does not have facilities for matching fixed strings. One can achieve the same effect, though, by first escaping all the special characters in the string to be matched. If a key is supplied as the first argument to this script, it will print only the lines in file that contain that key:
#!/bin/bash
printf -v script '/^%s\\x00/p' "$(sed 's:[]\[^$.*/]:\\&:g' <<<"$1")"
sed -n "$script" file
For more details on this code, see this answer.

Answer 2

I hit this problem as well, and the answer above is insufficient, and actually is specific to the answer that John1024 linked to for more details. It includes the null byte, which isn't applicable here.
To match on a fixed string, you can use this:
#!/bin/bash
# These can be anything
OUTER_STRING='hello $( string | is [ a ${ crazy } mess ] like wow; end'
INNER_STRING=' $( string | is [ a ${ crazy } mess ] like wow; en'
# This is the meat and potatoes
CLEAN_SED_STRING="$(echo "$INNER_STRING" | sed 's:[]\[^$.*/]:\\&:g')"
echo "$OUTER_STRING" | sed "s/$CLEAN_SED_STRING/ worl/"
To be cleaner, I made a bash function, that obscures the complexity. Tested on OSX, CentOS, RHEL6 and Ubuntu. Only two characters it can't deal with are the null (\x00) and the newline (\x0a)
function substitute {
if [[ "$#" == "2" ]] || [[ "$#" == "3" ]]; then
# Input from stdin
HAYSTACK="$(/bin/cat -)"
NEEDLE="$1"
NEEDLESUB="$2"
REGEX_FLAGS="$3"
else
echo "Usage: echo <HAYSTACK> | substitute <NEEDLE> <NEEDLESUB> [FLAGS]"
echo "Example: echo 'hello w' | substitute 'w' 'world'"
echo "Example: echo 'hello w' | substitute 'O' 'xxxxx' 'gi'"
fi
CLEAN_SED_STRING="$(echo "$NEEDLE" | sed 's:[]\[^$.*/&]:\\&:g')"
CLEAN_SED_SUBSTRING="$(echo "$NEEDLESUB" | sed 's:[]\[^$.*/&]:\\&:g')"
echo "$HAYSTACK" | sed "s/$CLEAN_SED_STRING/$CLEAN_SED_SUBSTRING/$REGEX_FLAGS"
}
# Simple usage
echo 'Hello Arthur' | substitute 'Arthur' 'World'
# Complex usage
echo '/slashes$dollars[square{curly' | substitute '$dollars[' '[]{}()$$'
# Standard piping
echo '
The ghost said "ooooooOOOOOooooooOOO"
The dog said "bork"
' | substitute 'oo' 'ee'
# With global flag and chaining
echo '
The ghost said "ooooooOOOOOooooooOOO"
The dog said "bork"
' | substitute 'oo' 'ee' 'g' | substitute 'ghost' 'siren'