Hi Chet,
Summary
*******
When a variable name and its' value are the same characters (a="a"),
a recursion error occurs.
Steps to recreate "problem"
***************************
Step 1:
1. Execute the command
.....................................................................
a="cat";b="dog";[[ $a -lt $b ]]; echo $?
1
.....................................................................
Step 2:
1. Change a="cat" to a="a".
2. Execute the command
.....................................................................
a="a";b="dog";[[ $a -lt $b ]]; echo $?
bash: [[: a: expression recursion level exceeded (error token is "a")
1
.....................................................................
In the steps above, I know I am using the numeric operator -lt to
compare 2 strings, in [[]]. But a recursion error seems a little
harsh, and seems inconsistent between Step 1's results and Step 2's.
The recursion error does not occur in Step 1, but it does in Step 2.
The only thing that changed was a="cat" to a="a". On the other hand,
if it is a usage error, which [] considers it to be, shouldn't the
return status be 2, not 1.
Occurs in the following
***********************
- GNU bash, version 4.0.35(1)-release (x86_64-suse-linux-gnu)
- GNU bash, version 4.2.0(1)-release (x86_64-suse-linux-gnu)
- OpenSuSE 11.2
Additional Info
***************
I came across the above when I was running through the
scenarios below to better understand tests, evaluation,
and return codes/exit status.
.---------------------+----------------.---------------.
| | | Return Codes |
| Expression | Evaluates '-------.-------'
| (a=5; unset b) | | True | False |
| | | Succ | Failu |
'---------------------+----------------+-------+-------'
| date | | 0 | - |
| date -a 2>/dev/null | | - | 1 |
'---------------------+----------------+-------+-------'
| (( a )) | 5 (^1) | 0 | - |
| (( a < 4 )) | 5 < 4 (^1) | - | 1 |
| (( a < a-1 )) | 5 < 5-1 (^1) | - | 1 |
'---------------------+----------------+-------+-------'
| (( $a )) | 5 (^1) | 0 | - |
| (( $a < 4 )) | 5 < 4 (^1) | - | 1 |
| (( $a < $a-1 )) | 5 < 5-1 (^1) | - | 1 |
'---------------------+----------------+-------+-------'
| [[ $a ]] | 5 (^2) | 0 | - |
| [[ $a -lt 4 ]] | 5 < 4 | - | 1 |
| [[ $a < 4 ]] | 5 < 4 | - | 1 |
'---------------------+----------------+-------+-------'
| (( b )) | '' (^2) | - | 1 |
| (( $b )) | '' (^2) | - | 1 |
| [[ $b ]] | '' (^2) | - | 1 |
'---------------------+----------------+-------+-------'
| [[ a ]] | a (^3) | 0 | - |
| [[ b ]] | b (^3 | 0 | - |
| | | - | - |
| | | - | - |
| | | - | - |
| | | - | - |
'---------------------'----------------'-------'-------'
(1) If the value of the expression is non-zero, the
return status is 0; otherwise the return status
is 1.
(2) The only variable regarded as false is unset or
value is null.
(3) The (bare)word expands into word, which is neither
null or unset, but rather the word itself.
[NOTE]
=====================================================================
- The execution of a command or program is expected to
return an error status integer, which will be 0 (true)
if the program completes successfully, and nonzero
(false) if an error occurs.
* EXIT_SUCCESS = 0
* EXIT_FAILURE = non-zero value
- When using compound commands, the exit status of 0 and
nonzero still stands, but there is an intermediary step
that deals with how conditional and arithmetic expressions
are evaluated.
- Arithmetic Evaluation ((...)): Within an expression, shell
variables may be referenced by name without using the
parameter expansion syntax.
=====================================================================
Thank you.
Peggy Russell
