Please advice why this happens.

from a Linux bash shell:

20406 pts/0    00:00:01 bash
26896 pts/0    00:00:00 ps

I run the follwing

str="a b c d"
printf "%s\n"  ` echo $str `

but from bash script


str="a b c d"
printf "%s\n"  ` echo $str `

it prints:

a b c d  

while the expected results from script should be like this:


What is missing in my bash script? Maybe bash ENV, or something like that?

I run also shopt command from my bash script and these are the results:

  utocd  off
  cdable_vars  off
  cdspell  off
  checkhash  off
  checkjobs  off
  checkwinsize  off
  cmdhist  on
  compat31  off
  compat32  off
  compat40  off
  compat41  off
  direxpand  off
  dirspell  off
  dotglob  off
  execfail  off
  expand_aliases  off
  extdebug  off
  extglob  off
  extquote  on
  failglob  off
  force_fignore  on
  globstar  off
  gnu_errfmt  off
  histappend  off
  histreedit  off
  histverify  off
  hostcomplete  on
  huponexit  off
  interactive_comments  on
  lastpipe  off
  lithist  off
  login_shell  off
  mailwarn  off
  no_empty_cmd_completion  off
  nocaseglob  off
  nocasematch  off
  nullglob  off
  progcomp  on
  promptvars  on
  restricted_shell  off
  shift_verbose  off
  sourcepath  on
  xpg_echo  off
  • 2
    Cannot reproduce this. It seems, that the echo part is additionally double-quoted. Please add bash version and the output of shopt to the question. – jimmij Jan 8 '18 at 17:55
  • @jimmij see please my update – yael Jan 8 '18 at 18:00
  • This might be related to this question posted here. Try echo -e $str instead and see if that works? – imbuedHope Jan 8 '18 at 18:03
  • this not help ( echo -e ) – yael Jan 8 '18 at 18:06
  • 1
    Did you mess with IFS variable, hmm? – jimmij Jan 8 '18 at 18:08

I can reproduce this behavior only in two cases:

  1. double-quoted command substitution:

    str="a b c d"
    printf "%s\n"  "`echo $str`"
  2. or changed Internal Field Separator (IFS variable), e.g.:

    str="a b c d"
    printf "%s\n" `echo $str`

In both cases output is

$ ./test.sh
a b c d

To repair first case just remove the quotes, and to restore IFS just set it to the default value somewhere above command substitution.

IFS=$' \t\n'

A little bit of explanation why the output is different when IFS changed and what does it have in common with double-quotes?

Lets start from the end:

printf "%s\n" a b c d

is obviously different than

printf "%s\n" 'a b c d'

In the first case we have four separate words, and printf output them one by one adding new line to them. In the second case the whole a b c d is treated as a single word and printf just output it as such to the terminal. And now should be obvious that the output of `echo $str` is treated as a single word when additionally double-quoted.

Now is where IFS starts to play a role. Namely, tt is used to split words after expansions, so with default IFS=$' \t\n' the expression echo a b c d outputs a b c d, but with IFS=, it becomes 'a b c d' - a single world, although quotes were not used explicitly. One can check that more clearly without variable:

$ IFS=,
$ printf "%s\n"  `echo a b c d`
a b c d

$ IFS=$' \t\n'
$ printf "%s\n"  `echo a b c d`

As a final note: it is better to use a $() form of command substitution, not backticks, but that's different topic.

  • well done its works – yael Jan 8 '18 at 18:48

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