add backslash before specific character

Question

we have file with many "%" characters in the file

we want to add before every "%" the backslash

as

\%

example

before

%TY %Tb %Td %TH:%TM %P

after

\%TY \%Tb \%Td \%TH:\%TM \%P

how to do it with sed ?

If it's a [cron file](https://unix.stackexchange.com/q/465556/117549), I would be cautious, in case the creator of the file ever *really* wanted to use % for sending stdin to the job. Consider [simpler wrapper scripts](https://unix.stackexchange.com/a/465575/117549) instead of gambling on precise syntax. — Jeff Schaller, Aug 29 '18 at 19:13

score 6 · Accepted Answer · answered Aug 29 '18 at 18:15

Pretty straightforward

$ echo '%TY %Tb %Td %TH:%TM %P' | sed 's/%/\\%/g'
\%TY \%Tb \%Td \%TH:\%TM \%P

but you can accomplish the same with bash parameter substitution

$ str='%TY %Tb %Td %TH:%TM %P'; backslashed=${str//%/\\%}; echo "$backslashed"
\%TY \%Tb \%Td \%TH:\%TM \%P

1 Answers1