On 09/06/2018 04:40 AM, Joshua Phillips wrote:
Escape sequences don't work in single quotes: $ echo 'hello\world' hello\world $ echo 'hello\'
Warning. Use of 'echo' and backslashes is non-portable. There are two classical behaviors: 1. backslashes are not special to echo unless you pass -e, so you also have to have -n to elide a trailing newline (this is the behavior of bash by default) 2. backslashes ARE special by default, so you don't need -e; and \c exists to elide a trailing newline, so you don't need -n (this is the behavior of dash by default, and the behavior required by POSIX; bash can also be configured to run in this mode via 'set -o posix; shopt -s xpg_echo')
Which makes it surprising that double backslashes get converted to single backslashes: $ echo 'hello\\world' hello\world Is this intended behaviour?
Yes. dash is obeying the POSIX-mandated behavior, and interpreting \ sequences by default. Since \w is not a known sequence, dash cheats and outputs \ as-is instead of giving you an error (although an error would be friendlier at reminding you that \ is active-by-default in dash). But since \\ is a known sequence, it gets interpreted by echo.
Bash behaves as I would have expected.
Rather, bash in its default mode does what you are used to, but violated POSIX. Bash in the mode that I mentioned above (set -o posix; shopt -s xpg_echo) behaves like dash.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
