mirror of
https://https.git.savannah.gnu.org/git/bash.git
synced 2026-06-27 07:43:07 +02:00
Chet Ramey
137 lines
3.7 KiB
Plaintext
137 lines
3.7 KiB
Plaintext
|
|
This is a description of the changes made to bash for increased ksh
|
|
compatibility.
|
|
|
|
1. $SECONDS
|
|
|
|
"Each time this parameter is referenced, the number of seconds
|
|
since shell invocation is returned. If this parameter is assigned
|
|
a value, then the value returned will be the value that was
|
|
assigned plus the number of seconds since the assignment."
|
|
|
|
Files changed: variables.c
|
|
variables.h
|
|
subst.c
|
|
general.c
|
|
shell.c
|
|
general.h
|
|
|
|
2. $TMOUT
|
|
|
|
"If set to a value greater than 0, the shell will terminate if a
|
|
command is not entered within the prescribed number of seconds
|
|
after issuing the PS1 prompt."
|
|
|
|
Files changed: shell.c (the implementation is not perfect)
|
|
|
|
3. $RANDOM
|
|
|
|
"Each time this parameter is referenced, a random integer is
|
|
generated. The sequence of random numbers can be initialized
|
|
by assigning a numeric value to RANDOM."
|
|
|
|
Files changed: subst.c
|
|
variables.c
|
|
|
|
4. $REPLY
|
|
|
|
"This parameter is set by the `read' special command when no
|
|
arguments are supplied."
|
|
|
|
Files changed: builtins.c
|
|
|
|
5. integer variables
|
|
|
|
`declare -i' (also export) makes a variable an integer (turns on
|
|
the integer attribute). When assignment is made to a variable with
|
|
the -i attribute, arithmetic expression evaluation is done on the
|
|
value before it is assigned to the variable.
|
|
|
|
Files changed: variables.h
|
|
variables.c
|
|
builtins.c
|
|
|
|
6. Arithmetic expression evaluation.
|
|
|
|
Here is the comment at the beginning of the new file `expr.c':
|
|
|
|
|
|
ksh-style expression evaluation.
|
|
|
|
All arithmetic is done as long integers with no checking for overflow
|
|
(though division by 0 is caught and flagged as an error).
|
|
|
|
The following operators are handled, grouped into a set of levels in
|
|
order of decreasing precedence.
|
|
|
|
"-" [level 0 (unary negation)]
|
|
"!" [level 1]
|
|
"*", "/", "%" [level 2]
|
|
"+", "-" [level 3]
|
|
"<=", ">=", "<", ">" [level 4]
|
|
"==", "!=" [level 5]
|
|
"=" [level 6 (assignment)]
|
|
|
|
(Note that most of these operators have special meaning to bash, and an
|
|
entire expression should be quoted, e.g. "a=$a+1" or "a=a+1" to ensure
|
|
that it is passed intact to the evaluator).
|
|
|
|
Sub-expressions within parentheses have a precedence level greater than
|
|
all of the above levels and are evaluated first. Within a single prece-
|
|
dence group, evaluation is left-to-right, except for the arithmetic
|
|
assignment operator (`='), which is evaluated right-to-left (as in C).
|
|
|
|
The expression evaluator returns the value of the expression (assignment
|
|
statements have as a value what is returned by the RHS). The `let'
|
|
builtin, on the other hand, returns 0 if the last expression evaluates to
|
|
a non-zero, and 1 otherwise.
|
|
|
|
Implementation is a recursive-descent parser.
|
|
|
|
Files added: expr.c
|
|
|
|
7. `let' builtin
|
|
|
|
Parameters may be assigned numeric values via the `let' builtin.
|
|
Each of its arguments is an expression to be evaluated. `let'
|
|
returns 0 if the value of the last expression is non-zero, and
|
|
1 otherwise.
|
|
|
|
Note that the "((...))" form of this command has not yet been
|
|
implemented; it requires changes to the parsing functions.
|
|
|
|
Files changed: builtins.c
|
|
|
|
8. $_
|
|
|
|
$_ is set to the last argument of the previous command line, after
|
|
expansion. It is still used as before when checking for mail.
|
|
Two new keybindings have been added to insert this into the current
|
|
command line (M-_ and M-.).
|
|
|
|
Files changed: mailcheck.c
|
|
execute_cmd.c
|
|
bashline.c
|
|
|
|
9. `cd -'
|
|
|
|
Equivalent to 'cd $OLDPWD'
|
|
|
|
Files changed: builtins.c
|
|
|
|
10. "ulimit -a"
|
|
|
|
"List all of the current resource limits (BSD only)."
|
|
|
|
Files changed: builtins.c
|
|
|
|
11. ${#@} and ${#*}
|
|
|
|
These expand to the number of positional parameters.
|
|
|
|
Files changed: subst.c
|
|
|
|
Chet Ramey
|
|
Information Network Services, Case Western Reserve University
|
|
chet@ins.CWRU.Edu
|