sed replace literal TAB

Question

I want to replace TABs in stdout with semicolons, by running sed from the ZSH shell.

I understand one can normally (in other shells?) use:

somecommand | sed 's/\t/;/g'

However, this doesn't work for me in ZSH-shell under FreeBSD. The \t doesn't match the tabulators. Why is this? I've also tried multiple backslashes (up to 5).

---

This does work:

somecommand | sed 's/[TAB]/;/g'

, where [TAB] is an actual TAB-character, inserted by entering Ctrl-V followed by the TAB button on my keyboard.

Answer 1

Use of zsh has nothing to do with it. The \t is a GNU extension to the regular expressions used in sed. On a BSD sed, you don't have the extensions, so have to use the literal tab.

Answer 2

One option is to prepare your sed script ahead of time with printf.

scr="`printf 's/\t/;/g'`"
somecommand | sed "$scr"

But Michael++... There may be other sed variants that also support printf-style escapes, but it's certainly not "standard".

Answer 3

If you know the output of the command is normal text (only tabs & printable text), you could use:

somecommand | sed -E 's/[[:cntrl:]]/;/g'

-E turns on "extended" regular expressions, which can contain character class names.