9

I am trying to understand local/environment variables and export/set commands.

$ set FILEM="razrax"
$ echo $FILEM

$ FILEN="test"
$ echo $FILEN
test

Please explain why echo $FILEM returns empty string

21

You're confusing bash with csh.

In bash like in any Bourne-like shell, set is the command to set options (shell configuration settings like -f, -C, -o noclobber...) and positional parameters ($1, $2...).

set FILEM="razrax"

Sets $1 to FILEM=razrax.

$ set FILEM="razrax"
$ echo "$1"
FILEM=razrax

The syntax for variable assignment in Bourne-like shells is:

VAR=value

(no space allowed on either side of =).

ksh and some other Bourne-like shells (mksh, pdksh, zsh) can also assign array variables with set though:

set -A array value1 value2

zsh, bash, yash and newer versions of ksh use this syntax instead:

array=(value1 value2)

In contrast, in csh or tcsh, the syntax is:

set VAR = value
set array = (value1 value2)

(spaces around = optional).

In rc/es shells:

VAR = value
array = (value1 value2)

(spaces around = optional).

  • Thank you for nice answer. The only thing I din't understand is what the difference benweet options and local variables "set is the command to set options"? – iJava Apr 21 '15 at 11:16
  • @iJava, set -C sets the -C option (same as set -o noclobber). set foo assigns foo to $1 (and $# is 1, ($2, $3 are unset if previously set)). Check your shell's manual for details. – Stéphane Chazelas Apr 21 '15 at 11:28
  • 1
    I don't understand what ARE options. Are these options that are send to programs like main (String[] args)? Or what? Where are they used? – iJava Apr 21 '15 at 11:32
  • 1
    @iJava, they are settings that affect the shell's behaviour. Again, RTFM – Stéphane Chazelas Apr 21 '15 at 11:35

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