Hi!
I've got some questions to the use of conditional expressions. I took a look
at the bash manual page, but nevertheless would like some more explanation.
First, there is the "/etc/profile.d/readline.sh" file:
When is the following expression true?
if [ -z "$INPUTRC" -a ! -f "$HOME/.inputrc" ] ; then
INPUTRC=/etc/inputrc
fi
bash manual says:
----------------------------
-z string
True if the length of string is zero.
-a file
True if file exists.
-f file
True if file exists and is a regular file.
SHELL BUILTIN COMMANDS
test and [ evaluate conditional expressions using a set of rules based on the
number of arguments.
0 arguments
The expression is false.
1 argument
The expression is true if and only if the argument is not null.
2 arguments
If the first argument is !, the expression is true if and only if the second
argument is null. If the first argument is one of the unary conditional
operators listed above under CONDITIONALEXPRESSIONS, the expression is true
if the unary test is true. If the first argument is not a valid unary
conditional operator, the expression is false.
3 arguments
If the second argument is one of the binary conditional operators listed
above under CONDITIONALEXPRESSIONS, the result of the expression is the
result of the binary test using the first and third arguments as operands. If
the first argument is !, the value is the negation of the two-argument test
using the second and third arguments. If the first argument is exactly ( and
the third argument is exactly ), the result is the one-argument test of the
second argument. Otherwise, the expression is false. The -a and -o operators
are considered binary operators in this case.
4 arguments
If the first argument is !, the result is the negation of the three-argument
expression composed of the remaining arguments. Otherwise, the expression is
parsed and evaluated according to precedence using the rules listed above.
5 or more arguments
The expression is parsed and evaluated according to precedence using the
rules listed above.
Next there is the "/etc/profile.d/umask.sh" file:
When is the following expression true?
if [ "$(id -gn)" = "$(id -un)" -a $EUID -gt 99 ] ; then
umask 002
else
umask 022
fi
id manual says:
-----------------------
-g, --group
print only the effective group ID
-n, --name
print a name instead of a number, for -ugG
-u, --user
print only the effective user ID
bash manual says:
----------------------------
PARAMETERS
Shell Variables
EUID
Expands to the effective user ID of the current user, initialized at shell
startup. This variable is readonly.
What I have some problems to understand is, how the parts of each conditional
expressions are connected in order to get one result.
Kind regards,
Leonhard.
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