How to substitute text from latex file preambles with sed?

Question

I wrote the following sed code that I haven't found the way to make it work...

sed -is 's/documentclass\{standalone\}/documentclass\[class\=memoir\]\{standalone\}/gp' *.tex

Am I using escape sequences the wrong way? The following is the error returned:

sed: -e expression #1, char 76: Invalid content of \{\}

Answer 1

In BRE (basic regular expression) mode (i.e. without the -E or -r command line option) braces are not special, while escaped braces are used for quantifiers like \{1,3\}. The error message is because standalone can't be parsed as a numeric quantifier. So you want {standalone}:

$ printf '%s\n' 'documentclass{standalone}' | sed 's/documentclass{standalone}/documentclass[class=memoir]{standalone}/gp'
documentclass[class=memoir]{standalone}
documentclass[class=memoir]{standalone}

Alternatively keep the escaped braces, but use ERE (extended regular expression) mode:

$ printf '%s\n' 'documentclass{standalone}' | sed -r 's/documentclass\{standalone\}/documentclass[class=memoir]{standalone}/gp'
documentclass[class=memoir]{standalone}
documentclass[class=memoir]{standalone}

Note that in either case, nothing in your RHS needs escaping.

See also:

• What characters do I need to escape when using sed in a sh script?

• Why do I need to escape regex characters in sed to be interpreted as regex characters?

Note also that at least in GNU sed, -is will edit the file in-place, creating a backup file with suffix s. If you want to pass the -i and -s options you must do so separately or in the other order -si. However iirc -i implies -s so the latter is likely superfluous.