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I've been wondering what's the difference between the two:

  • CAROOT='certificates'; echo $CAROOT - prints the value, uses ; as separator between two commands
  • CAROOT='certificates' echo $CAROOT - prints empty value.

I wonder why the former command works but the latter didn't?

The.Wolfgang.Grimmer
  • 141

1 Answers1

4

The following command line and its output can help explain how it works.

$ LANG=C bash -c 'echo LANG=$LANG'; echo LANG=$LANG
LANG=C
LANG=sv_SE.UTF-8

LANG=C with only a space works only on the following command, after that the old LANG setting is used again.

But why does it print an empty value in your second case? I would explain it like this: The variable will be expanded by the shell directly. This is different from the case with bash -c 'echo LANG=$LANG', where the variable is protected [by the quotes] at first, and will be expanded later, when the previous variable set command has already been processed.

The method with only a space, no semicolon is often used, when you want to change language temporarily, as in the following example where the heading is changed to the standard language (English).

$ df -h
Filsystem      Storlek Använt Ledigt Anv% Monterat på
udev               16G      0    16G   0% /dev
tmpfs             3,2G   1,6M   3,2G   1% /run
/dev/sda5          88G    32G    52G  39% /
tmpfs              16G      0    16G   0% /dev/shm
tmpfs             5,0M   4,0K   5,0M   1% /run/lock
tmpfs              16G      0    16G   0% /sys/fs/cgroup
/dev/sdb7         3,5T   998G   2,4T  30% /media/multimed-2
tmpfs             3,2G    20K   3,2G   1% /run/user/1000


$ LANG=C df -h
Filesystem      Size  Used Avail Use% Mounted on
udev             16G     0   16G   0% /dev
tmpfs           3,2G  1,6M  3,2G   1% /run
/dev/sda5        88G   32G   52G  39% /
tmpfs            16G     0   16G   0% /dev/shm
tmpfs           5,0M  4,0K  5,0M   1% /run/lock
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/sdb7       3,5T  998G  2,4T  30% /media/multimed-2
tmpfs           3,2G   20K  3,2G   1% /run/user/1000
sudodus
  • 47,864
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    Setting a variable with only space before a command sets that variable to be only available in that command's scope/environment check var='123' printenv var … however with the var='123' echo “$var”, $var gets expanded by the running shell before the echo command is run and even before var itself is set … hence the empty string … i.e. expansion happens first … the ; nests procedures in the order they will be executed and sets var in the environment of the running shell before the next procedure after ; including the expansion of $var happens … hence its value is printed. – Raffa Aug 01 '22 at 18:58
  • Yes, @Raffa, your explanation is good :-) – sudodus Aug 01 '22 at 19:03
  • +1 and :-) … Couldn’t include these in the first comment due to darn character limit. – Raffa Aug 01 '22 at 19:05